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AC compressor location?

May 28, 2012, 02:20:56 pm

This may be the stoopidest question ever asked on this forum, but where exactly is the compressor for the dash air conditioning located? I wonder if it has been removed by a previous owner or something? I don't see it on the engine anywhere. I was expecting to see a belt driven GM A6 type compressor or something like that. On the engine I see the compressor for the air brakes, the hydraulic pump, the alternator, and that's about it. In the front of the coach I see the condenser, evaporator, expansion valve, and the hoses going back to the compressor that I can't find... (puzzled look)... I have a 36' 1991 U300 with a 6V92.

Scott

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Re: AC compressor location?

Reply #1 – May 28, 2012, 02:45:17 pm

Scott, the A/C compressor on my 93, U300 is on the passenger side of the engine above the hydraulic pump at the back of the coach. It uses two v belts on the right side. I sort of remember yours has a rear radiator so yours will probably be different or at least harder to access.

Mine was just replaced at Foretravel. The compressor was $370 and labor about $200. Some compressors are up to $750. For once mine was the lowest price. That never happens.

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Reply #2 – May 28, 2012, 03:36:05 pm

That's where I thought the compressor should have been when I was looking at the engine. I'll ask the previous owner why he removed the compressor. Do you think it was a GM A6 type compressor, or what type compressor should it have? I suppose that would be a good question to ask Foretravel huh? I suppose I'll need to replace the missing compressor brackets too. Hopefully the previous owner still has them and will mail them to me, or I hope Foretravel has them.

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Reply #3 – May 28, 2012, 04:50:46 pm

Scott, if you give them your build number, they will know exactly which compressor you need and hopefully the brackets will be available. Can you take a photo of engine and post it? You've got me really curious now.

Bye the way, Foretravel's price for the new compressor was $10 less than the price from the local truck parts house when they included shipping.

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Reply #4 – May 28, 2012, 05:02:17 pm

I called the previous owner and he said the compressor is mounted on the bottom rear of the engine on the passenger side. I checked and it is there thankfully. I was expecting to see it mounted on the top front passenger side where there is an ominous empty area with threaded bolt holes as if something was supposed to be mounted there.

The previous owner said he thought the AC system takes R134a refrigerant... Do you think this 1991 model uses R134a or R12 refrigerant? I can't find any stickers saying what refrigerant to use.

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Reply #5 – May 28, 2012, 05:08:17 pm

It came out with R-12 but most have been converted. The connectors for an unconverted R-12 systems are different than a 134 connector. If you can hook up the 134 hoses, it has been converted. Is the dash air working at all?

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Reply #6 – May 28, 2012, 08:16:19 pm

It does appear to have different fittings on it, so maybe it's been converted to R134a? If so I'll probably have Stewart & Stevenson charge it tomorrow when I take the motor home to them for service on the Allison and Detroit Diesel. They don't have any R12 in stock. The dash air hasn't worked for about ten years so they'll probably have to change the receiver, evacuate the system, see if it can hold a vacuum, and then charge it. The dash air will probably pay for itself in diesel savings over running the generator while driving... if I drive it enough that is.

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Reply #7 – May 28, 2012, 10:41:42 pm

If the system hasn't run in 10 years I would expect you will need a new compressor (shaft seal probably leaking) and dryer.
I converted mine to 134A in 2003, invoice for parts shows:
Compressor: Seltec TM-15HD/HS  ($325)
Dryer: "3/8 O-ring dryer"  ($55) - has a sight glass

P.S.  Invoice was from a local parts house in San Diego not from Foretravel.

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Reply #8 – May 28, 2012, 11:12:41 pm

I'll find out how difficult / expensive it's gonna be to get the dash air working and then consider how long it will take to recover that expense in diesel cost compared to running the generator and roof air while driving.... and maybe I'll get it fixed tomorrow if practical.

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Reply #9 – May 29, 2012, 09:16:45 am

One good thing about the model you have is that the Dash Air works very well to cool the coach. We have never needed to start the generator to run the roof air, even in 105 degree temps last summer.

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Reply #10 – May 29, 2012, 10:32:29 am

Another thing to put into the equation is the cost of a new roof air at maybe $1200, plus the hours being put on the generator, and they are really expensive to replace.  I think that I would opt for using a new engine driven compressor system as maybe less costly over some years of ownership.

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Reply #11 – May 29, 2012, 11:51:07 am

Those are good points. I'm at Stewart & Stevenson now. The previous owner is pretty sure he converted it to R134a. I think they've got some here so I'll probably have them get the AC going today if possible.

I just filled the diesel tank before I drove down here. I think I got about 9 mpg on my 1100 mile trip from FL to TX at 60 mph with the generator running some of the time. My car only gets 13 mpg! (laugh)... I ran the fuel tank down as low as possible in case I had to weigh the coach for registration here in TX but they took the weight off the old title fortunately.

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Reply #12 – May 29, 2012, 04:14:41 pm

It looks like you drive a 1968 Impala from your Avatar. If so I had one that got only 8 mpg and that was with a 305, maybe Chevy's worst engine ever.

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Reply #13 – May 29, 2012, 05:25:01 pm

It's a 1965 Impala with a 283 V8. I was only able to get the Allison transmission serviced today because Stewart & Stevenson was so busy. They charged me $308 for changing the transmission fluid and external spin on filter. About $200 of that was labor... so I'll be doing it myself after this initial service.

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Reply #14 – May 29, 2012, 06:15:11 pm

Scott, my mistake on the car. There was never a better engine made than the 283. I Love It!!!

The $308 sounds very reasonable if you too have the same transmission as mine and they changed the fluid with Transynd, synthetic fluid. Mine takes 8 1/2 gallons of Transynd and it normally costs between $30 and $40 per gallon. If they didn't change the fluid, what did they do as part of their transmission service?

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Reply #15 – May 30, 2012, 11:18:31 am

My transmission uses no more than 18 quarts of Dexron depending on whether or not the external spin on filter was changed, which of course it was after sitting for several years without any service. They said the old fluid had a slight odor to it but it wasn't burned or discolored so the transmission is probably fine. If I'm reading the bill correctly the Dexron cost $63.68, spin on filter $7.26, environmental fee $11, shop supplies $1, and labor $220. I kinda need to go back there next week to get the engine / chassis serviced. I have the correct oil for the 6V92 and I'll see if I've got the correct filters or can get them. I need them to check the programming of the computer to see if they can adjust the shift point so it won't hunt up and down between 3rd and 4th gear on cruise control. The transmission shop told me the engine shop can do that... If so I'll start a post about that because other people will probably want to know if it really works. I think I'll take my dash AC to a little place I know that will probably be less expensive.

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Reply #16 – May 30, 2012, 11:25:28 am

...sorry, I missed your comment about the 283. The 283 is a short stroke V8 capable of 8500 rpm and tremendous horsepower at high rpm. The 305 is the opposite, with a long stroke for clean emissions, fuel efficiency, and low rpm torque. All of today's engines are long stroke, low rpm type engines... I really love engines as you might have guessed by the fact that I drove to Florida twice to get a 6V92

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Reply #17 – May 30, 2012, 11:54:03 am

Suspect you will find the 3rd/4th "hunting" is a function of the large gap between gear ratios in the four speed. The six speed would be a huge improvement as 5th would be a little taller than fourth now and give a several more MPH going uphill. This is the reason big rigs have so many speeds so the operator may select a gear to match the engine power/torque curve to the grade he or she is climbing.

300/350 HP Detroit 2 cycles are at their best at the higher end of the RPM range, not lugging down like Cummins, CATs. They displace only 9 liters so develop HP toward the top end of the operating range. I usually select 3rd gear and keep the tach at 2000 to 2100 when I encounter a "hunting" situation. You can't blow one of these devils up with high RPM and the transmission is designed to keep RV operators from damaging the engine through low RPM lugging.

Even in 3rd, I watch the engine temp to make sure I don't go much over 200 degrees. Read the boat forums as proper operating temperature is critical in achieving a long engine life.

And yes, it would be nice to loaf along below 48 mph in 4th gear without the Allison shifting down when on the flat but the Allison guys have tried to make the engine/trans package operator foolproof and as much as I dislike automatics, I think they have done a excellent job.

Pierce

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