Date: Sun, 05 Apr 1998 13:18:36 -0400

From: Marcus McGee <>

Subject: RE:GMC: (GMC) Conversion of AC to 134A

My original Transmode is having a problem with thw AC Compressor and it may need to be replaced. Has any one done the R12 to 134A conversion and what was involved? Any suggestions?




Date: Sun, 5 Apr 1998 13:30:58 -0500

From: "Gilbert R. Bethel" <>

Subject: Re: GMC: RE:(GMC) Conversion of AC to 134A

I have seen it done but you will get less cooling with 134a. It was recommended to me that I not use 134a on a vehicle that the air conditioner is marginal at best (i.e. a large van with single unit). I would keep it R12 if at all possible to ensure that the front ac kept the coach cool in the hot summer time. I guess you could run the Onan and the roof units but that would be hard on fuel economy.

If you decide to go with the 134a you will have to replace the expansion valve/orifice tube, drier and all of the o-rings plus clean out as much of the mineral based oil out to the system as possible. I would go to a reputable automotive air conditioner specialty shop to have it done. I would stay away from places like Pep Boys and the like as they do not specialize in change over. It will be expensive either way you go. If you think you can live with less efficiency from the unit then you may want to consider the changeover, otherwise bite the bullet and pay the high price for the R12. I don't know where you live but R12 is not very expensive in Mexico. It is illegal to bring cans of it back into the USA. I don't know about having a unit serviced in Mexico and then bringing the vehicle back to the USA. One would have to check on that.


Date: Sun, 12 Jul 1998 22:53:59 -0400 (EDT)

From: "Thomas G. Warner" <>

Subject: Re: GMC: A/C belt part numbers ??

Assuming you have a 455:

Dayco 15620

Gates 7619

GM (7/16" X62") 9433776

NAPA 25-15733

At 11:54 AM 7/12/98 -0500, you wrote:

>I lost the air conditioner belt this morning on the way home from work.

>Would someone have the part numbers for this belt?


>Russ Bethel


Date: Wed, 12 Aug 1998 21:41:26 -0700

From: "Skid" <>

Subject: GMC: Coach a/c performance

I've been following the "maiden trip from hell" thread since it's inception, and I have to admit that it's dimming my enthusiasm for the coach a bit. I made the mistake of letting my wife read over my shoulder, and now she says "let's get an ad in right away!"

All of you sharing your stories (including Bob, who started the whole shebang!) are to be commended for providing us with a lot of nervous laughter...

Regarding the coach a/c capacity questions, we've had several big coaches (a 35'er and a 38'), and both could be very comfortably cooled with just the front (roof) a/c running while on the road. They both had the Dometic (Penguin) units, if that matters to anybody. Our '76 Eleganza II has had it's one roof unit replaced with a 13.5K BTU Mach III Coleman unit that seems to do a good job also, although we've only been in heat up to about 100 degrees (with fairly low humidity). You folks in the heartland that have both high temps and high humidity may have a different story to tell...but with only 26' to cool, I'd be surprised if more than one a/c was needed, even with all of the windows!

My a/c experts here in the Seattle area (yes, we do use it around here 3 or 4 times per year!) tell me that the roof units to lose their charge over time, as do most a/c systems, it seems. They recharge them, but I didn't ask the price, as I've never had to have it done.

My $.02 - maybe only worth $.01?! <G>

Bill Marx


'76 Eleganza II - for sale (really...), as it's just too small for us

to full-time in...


Date: Thu, 13 Aug 1998 11:59:05 -0400

From: "Bartz, Paul" <>

Subject: RE: GMC: Coach a/c performance

Bill, et al:

I agree that one rooftop a/c unit should be sufficient to cool the interior of the coach.

Several years ago, while on a trip into the Houston area during July, with temps in the upper 90's and same with humidity, had no problem keeping cool with our rooftop a/c unit (original).

Anyone experiencing problems otherwise, recommend you have the output of your a/c unit checked out.

Paul Bartz



Date: Sun, 16 Aug 1998 19:55:52 -0700


Subject: GMC: Rooftop Air conditioner

My Rooftop A/C compressor was kicking out after 3-4 seconds. While looking it over for what I don't know, one of the leads to one of the three capacitors broke. We found the A/C to work perfectly without that wire attached. The capacitor was replaced and the A/C works fine whether the wire is attached or not. Now my question is what the wire is supposed to do. I know this is not much information to work with, but I don't know how to identify which capacitor does what, let alone which wire is which. Just in case You haven't guessed by now, the extent of my knowlege of Air Conditioning is that it's supposed to blow cold air.

Thanks for any wisdom, speculation, or whatever You might offer here

Tim Timothy


Date: Sun, 16 Aug 1998 21:28:21 EDT

From: <>

Subject: Re: GMC: Rooftop Air conditioner


There are 3 capacitors you say. Ok I have not even got close to looking at mine but I am going to take a leap at this one. I worked on ACs 30 years ago so I may be a little rusty here.

Cap 1 is a start cap for the compressor, If this one is bad compressor will shake and shimmy when trying to start. It will do this for a few seconds then kick out on thermal overload---you will hear a click and compressor will shut down.

Cap 2 is a run cap for the compressor, if this one is bad the compressor will fire and try to run. It will sound like it is changing speeds the pitch of the sound will go up and down. On a cool day it may be able to run. Once head pressure builds on a hot day it won't be able to. Again out on thermal overload.

Cap 3 is a run cap for the fan motor. Again I have not looked but it should be the smallest of the 3. You might get things to work with a lead off this one. The problem is that the fan motor will not be operating at its design speed. This will cause head pressure to rise------ok on a cool day not on a hot. Everything will have to work harder.

A word of warning here If you do not know your way around these things be careful-----they can hurt you. Before touching a cap put a screwdriver across the two connections to discharge it. These things will hold a charge for a long time. Touch both connectors and you will be picking yourself up of the ground. At our ages you could do worse. Just short it out before you

play with it.

Best I can do with out grabbing the Bible.

Take Care



Date: Sun, 16 Aug 1998 21:01:20 -0700


Subject: Re: GMC: Rooftop Air conditioner

Per the paperwork I have available, the start capacitor is the round cased one of the Three. It starts normally(I think), NO shaking or shimmying like it is having trouble getting underway. Can't hear "click" - posssibly due to noise of compressor/fan motor


> Cap 2 is a run cap for the compressor, if this one is bad the >compressor will fire and try to run. It will sound like it is changing >speeds the pitch of the sound will go up and down. On a cool day it may >be able to run. Once head pressure builds on a hot day it wont be able >to. Again out

on thermal overload.

The best I can tell from the paperwork and what I understand that You're

saying, this is our culprit. It is the largest of the three.

(30uf) The wire in question goes from here to what appears to be a relay.

Thanks Arch,

And I enjoy your writings. I see no "rambling" as You say.



Date: Sun, 16 Aug 1998 22:48:54 EDT

From: <>

Subject: Re: GMC: Rooftop Air conditioner

In a message dated 98-08-16 22:00:51 EDT, you write:


The best I can tell from the paperwork and what I understand that You're

saying, this is our culprit. It is the largest of the three.

(30uf) The wire in question goes from here to what appears to be a relay.



It should be the biggest. 30 micro f about right. The relay is the start run relay. It starts the compressor on the start cap and then switches it to the run cap. The relay could also be bad but from my experience the cap is more likely to fail. Low voltage at campgrounds causes that. Good luck. If I can be of anymore help holler and I will get out the Bible and see if I know what I am talking about.

Take Care



Date: Sun, 16 Aug 1998 22:08:27 -0700


Subject: Re: GMC: Rooftop Air conditioner/Unnecessary Wire????

Thanks Arch,

I now know the capacitor was at least part, maybe all of the original problem. It has been replaced and the A/C works fine WITH or WITHOUT the wire mentioned. I was trying to understand the purpose of the apparently unnecessary wire, which, when attached will not let the A/C function with the faulty capacitor installed.



Date: Sun, 16 Aug 1998 21:25:46 -0700

From: "mr.c" <>

Subject: Re: GMC: Rooftop Air conditioner

I don't know for sure based on what you said, but the capacitors are usually starting capacitors for the motors and are disconnected when the compressor comes up to speed. It is an aid to getting them going, and they can start by themselves but it makes them easier to start. I hope that is what the capacitor did that you were talking about.

Al Chernoff


Date: Mon, 17 Aug 1998 07:56:02 +0100

From: "Donald W. Miller" <>

Subject: Re: GMC: Rooftop Air conditioner/Unnecessary Wire????

My guess is, though the compressor motor runs without the capacitor, it probably draws more current and the compressor windings run hotter. I would suggest you make certain it is properly wired.

I worked one summer for Westinghouse as an intern in their industrial A/C design lab. The test cells were always well ventilated because when a compressor using R22 fails it can produce Phosgene, a highly poisonous gas. While I was there, we had compressors fail and blow out the seals around the electrical connections. There is also a flash fire as the oil comes out of the system under pressure and burns violently.

Those guys had enough respect for the potential danger they made a lasting impression on me so 45 years later I still prefer R22 compressors mounted outside the house over those in bedroom windows.

On the other hand, I have never heard of it being a problem outside the lab because the thermal switch keeps it from occurring.

I have several A/C service oriented books which do not mention it so I do

not know if this is well known among people who service A/C units or just to

those who design them.

Next time you hear an R22 compressor thermal switch click, you can count among your blessings the fact that it worked.



Date: Mon, 17 Aug 1998 12:02:06 -0700

From: (Dave Lowry)

Subject: GMC: Roof A/C

Arch (or anyone else who might know);

The recent post re: capacitors reminded me of another abnormality I have not yet dealt with. Whenever we start the roof a/c, the fan comes on immediately but the compressor doesn't kick in for 60 to 90 seconds. Once working, it cools well and has never failed, but I'm worried that one day it will. We're about to leave on a coast-to-coast-to-coast trip (7,000 mi. or so), and will certainly need the a/c to work.

Is it likely to fail without further warning? How can I prevent failure, or fix it when it fails?

I can't get onto the roof to fix it myself, but I'd sure like to have an idea what was wrong before I had someone else get up there an play with it at my expense.

I travel with all the manuals (thanks to Cinnabar) and many useful snips from the posts on GMCnet, but I haven't found any mauals for the old a/c.

Any ideas what's going on?

TIA, Dave


Date: Mon, 17 Aug 1998 16:00:51 -0400

From: "Bartz, Paul" <>

Subject: RE: GMC: Roof A/C

If I'm not mistaken, the roof top A/C manual points out that there is a delayed start for the compressor. I'm not at home now and don't have my manual available to me to tell you the reason.

Paul Bartz


From: Chuck Blanford []

Sent: Monday, August 17, 1998 1:48 PM

Subject: Re: GMC: Roof A/C

I am also interested in the answer to this post. My compressor doesn't kick in for several minutes, but seems to function well and stay on line once it does.



Date: Mon, 17 Aug 1998 16:01:46 -0400

From: Patrick Flowers <>

Subject: Re: GMC: Roof A/C


Has this unit always behaved this way as long as you've owned it or did it just start doing this recently. IIRC, the roof a/c on my father's old HRC trailer also had a delayed start on the compressor. This was a safety feature to prevent compressor damage if the power went out and came back on quickly. It allowed refrigerant pressures to equalize before the compressor restarted.

Patrick Flowers


Date: Mon, 17 Aug 1998 14:06:36 -0700

From: "Heinz Wittenbecher" <>

Subject: GMC: Is there an Alternative to Roof Air?

One of my pet peeves is the noise of the roof air unit. I have a Dometic

15000BTU with the heat pump and unfortunately it only has 2 fan speeds but

even my previous one was 'noisy'.

I know that air has to circulate, etc, etc but isn't there an alternative

even for a coach our size?

I suppose one gets used to the noise (does one?), but as I live in the more

temperate area of the Northwest (actually Southwest of CanuckLand) I get spoiled by not having to run the AC all the time. Then when I hit CA or

Texas it's 24hour GenSet/AC. Nothing like the roar of the AC unit to kill

the serene settings of nature.

BTW, any chance someone out there has the same unit and managed to 'quieten

it down some'?

Of course the real breakthrough I'm waiting for is a tractor beam on the

highway that the GMC can lock onto, i.e. a real autopilot.

Oh well, AC first...

Thanks in advance for any suggestions.


sweatin' it out in CA.


Date: Mon, 17 Aug 1998 18:36:14 -0700

From: "mr.c" <>

Subject: Re: GMC: Roof A/C

Many of the a/c units deliberately start the fan and then the compressor about a minute or two later. Mine work that way and I just wait a few minutes and then the compressor comes. It may be that your's is the same.

regards Al Chernoff


Date: Mon, 17 Aug 1998 21:52:04 EDT

From: <>

Subject: Re: GMC: Roof A/C


Your AC is working just fine. Mine takes 3-5 min before the compressor comes on. It is a time delay built into the unit. I have been told and I have read several reasons for it. 1. It gives the genset time to settle before it drops the big load of the compressor on it. 2. If some one turns the unit off and then right back on (or a power glitch) the fan has a chance to equalize head pressure before the compressor tries to come back on.

These are just 2 of the many I have heard--------these just make the most

sense to me. PLEASE understand I have not worked on mine yet. I am only telling you that Mine has a longer delay (fact) and other sources have told me this is normal. (Yes I too was worried at one time).

Take Care



Date: Mon, 17 Aug 1998 22:01:54 EDT

From: <>

Subject: Re: GMC: Roof A/C

In a message dated 98-08-17 16:07:30 EDT, you write:


Has this unit always behaved this way as long as you've owned it or did it just start doing this recently. IIRC, the roof a/c on my father's old HRC trailer also had a delayed start on the compressor. This was a safety feature to prevent compressor damage if the power went out and came back on quickly. It allowed refrigerant pressures to equalize before the compressor restarted.

Patrick >>

NOW you have seen it from two different people------it might be true.

Take Care



Date: Mon, 17 Aug 1998 12:02:06 -0700

From: (Dave Lowry)

Subject: GMC: Roof A/C

My 78 Kingsley works the same with the fan coming on and then the compressor

90 seconds latter. I think it is the way the system works. It allows the fan to come up to speed and then compressor to reduce head pressure when it cycles on and off. So you should be ok, and have a great trip.

Thank You

Tim Jones


Date: Tue, 18 Aug 1998 12:04:13 +0100

From: "Donald W. Miller" <>

Subject: Re: GMC: Is there an Alternative to Roof Air?


I agree with you about the Roof A/C noise. I have had roof air for 30 years and never adjusted to it although I don't mind it when asleep.

I hope my Alternative to Roof Air works OK, otherwise I am going to be

really stuck in the deep stuff this time.

As part of our refurbishment I have already replaced both roof A/C units

with some nice quiet ventilators.

My alternative is to greatly enhance the Dash Air output and make it our

only A/C.

With the 455 engine idling, the oem compressor pumps enough freon to out

perform my two roof air units. Unfortunately, other areas of the dash air

system are lacking and do need some upgrading.

Jim Bounds gave me a thought provoking response on 6/25/98 and Jim, I am

looking forward to discussing this further with you on the phone soon.

Jim has installed a second evaporator under the refrigerator which operates from the dash compressor and he says with it, the dash air can cool the coach very well. This setup is similar to the dual air units often seen in Suburbans and Vans.

I recently modified my dash air box for enhanced air flow. I need to do some further testing before I would want to recommend my modification to anyone else but it looks promising so far.

Once my modified dash system with a second evaporator are performing well, my next step will be to add 120 volt shore power capability to the Dash Air.

This will involve either adding a 120v compressor up front or driving the oem compressor with a 120v motor and a belt. I am still pondering the tradeoffs but leaning toward the belt driven scheme.

Two 14" 12 volt fans will cool the A/C condenser in front of the radiator.

They will cycle with the compressor.

By eliminating the roof air I eliminated our largest genset loads so our

Onan is being replaced by a high output 12 volt alternator and a 2500 watt

sine wave inverter.

When boondocking the idling 455 engine will make enough electricity and it

idles quieter than the Onan. During quiet hours AC is available from the

inverter and house batteries.

The idling 455 also heats the hot water, and heats or cools the interior as


For electricity I am using a large frame Leece Neville 12v alternator as they are very dependable and produce well over 100 amps with the engine idling. The inverter is a Statpower unit.

For me the most troublesome factor to overcome is the idea of letting an engine idle for long periods of time.

With leaded fuel and older engines there can be some problems, but the experts tell me not to worry about this engine with unleaded fuel.

For you weight watchers, it now looks like this one is going to have lost

over 1500 lbs. when finished.

My GMC mods are now on hold until mid September. Getting the 1970 Twin

Comanche ready to fly out to Victoria, B.C. in a couple of weeks for some

fun and frolics.



Date: Wed, 19 Aug 1998 21:09:28 -0700

From: "Tipton, Eric" <>

Subject: RE: GMC: Re; Is there an alterternative to roof air?

I have a 1977 Eleganza with the "improved" air flow. I am still disappointed with the air flow. I attended a seminar several years ago given by Duane Simmons called "Separating Hot From Cold" which told about A/C airflow theory & maintenance. I went through the system at that time & resealed it completely. I have an external ball valve to control heater water flow. I need to look at the system again I guess.

We used to travel to Phoenix with a daughter at ASU. We added a supplemental evaporator under the street side couch. I blow very cold air. I may add either a similar unit in the cockpit or a small unit under the copilot chair in the metal box.

For everyone's info:

The supplemental evaporator is an SCS/Frigette Model U4034 purchased in 1994.

Address: SCS/Frigette; PO Box 40557; Fort Worth; TX 76134 (817)293-8014


Purchase at Hal's Auto Air in Sacramento, CA

I mounted the evaporator and the A/C lines. The A/C shop the installed two compression T's to integrate in the dash air.

Eric Tipton

-----Original Message-----

From: Philip L. Stewart []

Sent: Wednesday, August 19, 1998 8:59 PM


Subject: GMC: Re; Is there an alterternative to roof air?


I believe you and Donald are correct in suggesting that there

must be an improvement possible to the stock dash air handling system.

On my '76 Transmode with the type two upgrade center auxillary air outlets there is woefully poor air flow from the two vents. However, whenever I take off the plastic plenum hanging under the dash and run the AC on max, there is a veritable hurricane of frosty air blasting out of the evaporerator/ blower box. Unfortunately without the plemum the air flow is directed straight out onto the floor and it quickly is lost into the living area and does not provide much relief to the occupants of the cab.

There must be a way of directing more of the air to the driver and passenger seats. Expirements with cardboard boxes and tubing temporarily taped to the under dash outlets show that in my coach dash air comfort is a possibility. The problem is how to do a modification that is neat, attractive and doesn't ruin the appearance to the otherwise well designed and eye pleasing GMC dash. Any one have any ideas on this?

BYW, I saw a coach where Zeb Frady of Southland Mohtorhome Center in Buford GA had installed an auxillary evaporator and blower box on the sloped floor board in the center of cab under the dash. It looked like a commercially available unit and Zeb said that it greatly improved cooling of the cab and coach. Anyone interested could get more details by calling Zeb.

Phil Stewart


Date: Thu, 20 Aug 1998 09:36:26 -0400

From: "Bartz, Paul" <>

Subject: RE: GMC: Re; Is there an alterternative to roof air?


Was the seminar by Duane any different than the one by the same name that Zay Brand gave at the Mar 97 GMCMI Boerne Rally?

Paul Bartz



Date: Fri, 21 Aug 1998 15:13:30 EDT


Subject: Re: GMC: GMC Motorhome Digest V1 #267

Paul Bantz

Back in the spring of 94, Zay Brand & I worked together to determine what

maintenance items & what up-grades were necessary to make our Dash Air Conditioners acceptable. I have a '73 & Zay has a '77 , so we were able to address the entire fleet. Major change occurred in two year increments, with the best being the '77/'78 coaches. After our recommended maintenance/up-grades we were both happy with the Dash A/C operation. Sealing the doors to separate the Hot from the Cold is a small job with big pay back. Also, converting the A/C into a completely air recirculation system was the biggest pay back. A simple 10 minute job for all systems except for the coaches that have the added "Air Horn" to the center/bottom dash. This system is called the "Type II" system & requires more work to achieve some Air recirculation ...a half-day job, but worth it. With my Privacy Drape closed behind the Pilot/Co-Pilot seats, recirculate mode, outside air at 100 degrees, I am able to obtain 38 degree air out of my center a/c duct. After a while, it gets too cold & we open slightly the drapes to get the desired cooling. Needless to say, we are now happy w/our a/c system. The Dash A/C can not cool the entire coach on a Hot Day (above 100 degrees), but does a great job of cooling the

cockpit area.

Zay & I both are planning to be at the Marion NC Convention in October

,if any one has any questions, you can see us there. Also I will try to

bring copies of Zay's "Separating Hot from Cold" briefings document. The

March 97, Boerne Texas, GMCMI briefings was an update of the April '94

briefings at Lake Tahoe's Roundup (GMC Western States). Only minor

updated material in the Boerne Convention briefing.

In some cases, only adjustment of the Temperature Door for full closure

makes a significant difference in cooling. Shutting off the Hot Water

from flowing thru the Heater while in the A/C mode is also very helpful.

The adjustment is located behind the Control Panel as an in-cable adjustment. Adjust for full Temperature Door closure as observed out front, drive side of A/C & Heater Box.

Duane Simmons


Date: Sat, 22 Aug 1998 18:34:04 -0500

From: "Mark Grady" <>

Subject: GMC: Roof top unit won't keep running (reply)

Tim --

I haven't looked at a schematic for one of these in years, but for what it's


The time delay (mars) relay is only used in the circuit at startup.

If the compressor is only running for a few seconds, then it's either overloaded (possibly oil slugged) or the run cap is shot, which causes it to draw too much current and trips the guardette.

The guardette is a small round circuit breaker on the side of the compressor, usually right beside the start/run relay. It's usually under a cover with a wire retainer that looks like a handle on can of paint. (bail)

For most sealed compressors, if you "remove the wire which we "THINK" is from the compressor overload switch" it shouldn't run at all, since this is a series circuit.

"The compressor actually gets quite cold in operation. Is this normal?"

No. It should be warm (or hot) rather than cold, depending on your local temperature.

There may be some residual 'chill' on the suction (low pressure) line, but the compressor probably isn't running long enough to get up to temperature,

so it seems 'cold'.

> Do I have a second bad Capacitor?

I'd guess that you do, or else the start/run relay is shot. Those are the most common problems with these sealed units.

> I don't have the time delay so many have mentioned.

> Where can I get the "Mars" or equivalent relay?

If the circuit for the 'soft start' wasn't included in your roof top unit at the time of build, it's difficult to add one in a simple and direct way.

Not having one isn't the end of the world, it just makes it easier on your

genset (and shore power connection) by making sure that the recirculating

compressed refrigerant has time to equalize (high side head pressure

reduces) before the compressor tries to start again.

Without the delay relay, the guardette on the compressor itself will trip,

or else the circuit breaker ahead of that will trip due to too much current


A fast recycle attempt has the compressor motor trying to start turning

against the remaining pressure from the previous run cycle.

It can't start to turn against this residual pressure, so it draws too much

current. To keep from burning out the windings of the motor (which is what's

inside the compressor, it trips the guardette (circuit breaker) which is

sized just right to protect the motor itself.

I'd try another capacitor first if your the home handy man type, or get a local refrigeration person to take a look see at your problem.

Other than the fan motors they use, these roof top units are a lot like window air conditioners, so a good appliance man can help you out. It doesn't sound like you've lost your refrigerant charge, so its most likely an electrical problem.

With R-12 no longer available and R-22 scarce (and expensive), if you toast your motor windings, I'm not sure what you have left to work with, so you might want to seek out a pro.

Those are my .02 worth.



Date: Sat, 22 Aug 1998 17:23:50 -0700


Subject: Re: GMC: A/C Mars relay

I'm again having the problem of my roof A/C compressor running 3 or 4 seconds and cutting out. The RUN capacitor was replaced with a used one. It worked fine for a few days. I can remove the wire which we "THINK" is from the compressor overload switch and the unit works fine. The compressor actually gets quite cold in operation. Is this normal? Do I have a second bad Capacitor? Could the compressor overload switch be bad? Could the relay be bad? I don't have the time delay so many have mentioned. Where can I get the

"Mars" or equivalent relay?

Thanks Again, Tim


Date: Sun, 30 Aug 1998 18:31:22 -0400

From: "Tom Winslow" <>

Subject: GMC: AC kills ONAN

I have a situation.

Our 1974 26' Eleganza SE has a single roof AC (Caravan Mark IV). The AC works fine while connected to the 'shore power' and the ONAN seems to be OK so long as I am not running the AC. But, If I run the AC using the ONAN power, the ONAN dies about the time the compressor 'kicks in'.

We have adjusted the voltage to upward about 125vac and that does not seem to help.

Any help, suggestions?

Thomas P. Winslow


Date: Sun, 30 Aug 1998 18:34:04 -0500

From: "Russ Bethel" <>

Subject: Re: GMC: AC kills ONAN


I would suspect the engine is not able to supply the horse power needed to run the air conditioner. I would look at the fuel system, possibly the governor or carb. I looked in the Onan service manual and it did not address your situation, or at least I didn't find it. You may have the carb too lean to supply the need fuel for the power needed. Other than that maybe Jim Bounds' Onan man may be able to help you.

Russ Bethel


Date: Mon, 31 Aug 1998 02:56:49 -0400

From: Jim Bounds <>

Subject: Re: GMC: AC kills ONAN


My first question would be, "Have you done anything recently to change the generator or AC units?" Many times, there is a recent event that has changed the operation of either that might cause a problem (ie. rewiring, oil change, generator degrease, etc.)

If not, then you may have something that happened without ?


Date: Sat, 23 Jan 1999 17:09:19, -0500


Subject: GMC: Air Cond. Condenser

Working on the theory that if it happened to me---- you are next

Looking at the Air conditioner Condenser hooked to the front of the radiator. Look at the right side mounting. The top where the condenser mounts to the rubber mounted frame with a single bolt. Mine has broken off from the condenser and has been wearing on the tubes of the condenser. It is almost worn through which would let out all of the Freon.

The bottom bolt is entirely missing. Take a look at the whole mounting. Might save you some money.


- --

Gene 76Palm Beach /Or/CA


Date: Wed, 3 Feb 1999 20:49:31 -0600

From: "Travis Martin" <>

Subject: GMC: Refrigerant used in roof air units?

Can anyone tell me which refrigerant the roof air units use? R12 or R22?

While you're at it, tell me how much trouble it is to remove the roof air unit I better off to work on it in place?

I don't relish trying to balance myself and tools on the roof while working; looks like it would be easier in the long run to take it down, fix it (got a leak somewhere) and then re install it; I'd like to hear from someone who's done it...

Thanks in advance,



Date: Wed, 03 Feb 1999 22:17:56 -0700

From: Darren Paget <>

Subject: Re: GMC: Refrigerant used in roof air units?

Easy to take down with a friend. They are very heavy. Real heavy. Don't try

this by yourself. The wiring will have to be disconnected and the unit will

have to be unbolted. They are bolted from the inside out. There is a bolt in

each corner which connects to a metal plate. The unit is just clamped to the

body with these four bolts. Be careful and have fun. Darren



Date: Thu, 4 Feb 1999 07:09:36 -0500

From: "Mark Grady" <>

Subject: GMC: Refrigerant used in roof air units? (reply)

Travis --

If my memory is right, they use R-12. 22 has a lower heat absorption rate efficiency, and these units need as much capacity in a small space as they can get.

Do take the advice of the post from Darren. These baby's are heavy and that roof is kinda' flexy.

Put down a couple of layers of 1/8" masonite or thin paneling to spread your

weight around. I've found that two or three layers distribute your weight

better than one thick board, which won't bend enough to contour to the

roofline itself. Just for what it's worth.

Mark Grady




Date: Thu, 4 Feb 1999 11:18:05 -0500

From: "The Hamiltons" <>

Subject: GMC: Roof Air Refrigerant


The refrigerant in the original roof air conditioners is R-22. Even the smaller rear AC unit on a two AC coach is heavy and difficult to handle.

It takes at least two men to take an air conditioner off the roof or put it on - or a fork lift. I would recommend three people. A method I've used and seen used a couple of times is to lay a 12-foot ladder from the roof of the coach to a 10-foot step ladder, place the AC unit on the horizontal ladder, slide the unit out towards the step ladder, one, or better, two people can hold the unit while another removes the step ladder and lowers the ladder and AC unit to the ground.

Kathy & Al Hamilton

76 Eleganza II

Kingston, Ont


Date: Thu, 04 Feb 1999 21:16:28 -0500

From: Jim Hall <>

Subject: GMC: R12 replacement

I am in the AC business, We use a product called "Hot Shot" to replace R12 freon in systems. It is a " drop in " replacement. You do not need to replace seals or oil or metering devises to use, is also is more efficient than R12. After fixing any leaks you pull a vacuum to remove the old R12 and refill with the same lbs of "Hot Shot". We have used this product for 3 years with no problems. Of course you must have an EPA license to purchase. If it leaks down you must vacuum all out and replace total charge, usually less than 3 lbs or so.

Jim Hall

77PB in Pawleys Island


Date: Fri, 5 Feb 1999 01:13:36 EST


Subject: Re: GMC: Refrigerant used in roof air units?

Just changed my 13,500 btu roof AC for a reverse cycle unit. My method requires an overhead beam (shade tree?) and a light weight block and tackle capable of lifting the AC unit (about #120). Position the motorhome with the

AC centered under the lifting support (overhead beam), remove all attaching hardware, make a rope or strap sling to attach the AC to the block and tackle, hoist the AC clear of the motorhome, tie off line. Now drive the motorhome out from underneath the suspended AC and lower the unit to the floor or table. Reverse procedure to install.

Worked for me. One man job! BTW I now have extra AC unit available, works great just doesn't heat.


77 Eleganza II, in sunny Orlando



Date: Fri, 5 Feb 1999 01:42:32 EST


Subject: Re: GMC: Re:rooftop Air Conditioner


The reverse cycle units work well until the outside temperature falls below 40, then they quit. Fine for Florida!

Nelson 77 Eleganza



Date: Fri, 5 Feb 1999 02:31:30 EST


Subject: Re: GMC: Alternative refrigerants


Anyone considering alternative referigerants shoud surf on over to the EPA's web site at You'll get the official word.

BTW, hydrocarbon-based referigerants are generally illegal.

Rick Staples

'75 Eleganza

Louisville, CO


Date: Fri, 5 Feb 1999 12:27:01 EST


Subject: Re: GMC: Alternative refrigerants

In a message dated 2/5/99 0:32:19 AM MST, writes:

> Anyone considering alternative referigerants shoud surf on over to the

> EPA's web site at You'll get

> the

> official word.


My apologies, I was falling asleep at the keyboard last night! I don't

know where that URL came from, but try

Rick Staples

'75 Eleganza

Louisville, CO


Date: Fri, 05 Feb 1999 21:59:43 -0700

From: "mr.c" <>

Subject: Re: GMC: rooftop Air Conditioner

I put in a new unit that has a heat pump and puts out 15K of cooling and 12K of heating. Works great unless the temperature is less than 40 degrees. Does make a little more noise as it is pushing lots of air.

Rob Teed wrote:

> Were going to purchase a rooftop air conditioner for a 26' Painted Desert.

> Any input on brands,size, color <G>

> Also wonder how well the heat units work with the air conditioners

> Thank,

> Rob Teed 74 Painted Desert


Date: Sat, 06 Feb 1999 21:57:28 -0700

From: "mr.c" <>

Subject: Re: GMC: rooftop Air Conditioner

New unit was a Duo-therm. One thing about it that I recommend is that once

you buy it they send you a certificate for a three years service contract extension for a hundred plus. I think that is great because if it fails, the

cost of repair is far greater than the cost of the warranty extension.


Al Chernoff

77 Eleganza II