Automotive Air Conditioning Information Forum (Archives)

deandec on Thu September 20, 2012 5:28 PM

Year: 1995
Make: Country Coach
Model: Magna
Engine Size: 300
Refrigerant Type: 134a
Ambient Temp: 80
Pressure Low: 0
Pressure High: 140
Country of Origin: United States

My 38' diesel pusher Motorhome has an Over The Road system by RVAC, Inc of Texas. OTR means AC is provided at the rear of the coach and at the dash from the same compressor.

The System worked fine except for about 1.5lbs of 134a loss this spring. I topped off the system and a few weeks later the Compressor Clutch caused the power fuse to fail.

I had the system recovered and then replaced the Compressor and Dryer.

I then evacuated the system for 30 minutes and it held vacuum for another 30 minutes, before I began to recharge the system.

I have installed the required 5 lbs of 134a listed on the vehicle.

The low side reading is 0. The high side reading is 140.

Prior to the clutch failing I had readings of 30 low and 200 high.

Should I keep adding 134a even though I am at the proscribed 5 lbs of 134a installed? Or is it possible I have a pressure leak even after holding a vacuum for 30 minutes successfully.

Any advice would be great.

GM Tech on Thu September 20, 2012 5:41 PM

You probably have a TXV filled with shrappnel from the first compressor- now it and the system is plugged up-- your clutch did not fail by itself -it was the result of something else... it was probably smoked due to a seized compressor- then blew the fuse-- who ever evaluated the system failed to recognize this failure mode and took the easy way out, and now you are paying for it.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

deandec on Thu September 20, 2012 6:30 PM

Thanks for the rapid response.

I guess I do not understand the term "seized compressor".

The 17 year old 90,000 mile compressor spun freely on the drive belt with no associated groans, squeeks or other weird noises. Actually, for a short while, the clutch would engage with direct 12vdc power. Then, the resistance dropped to zero ohms.

Can the compressor be seized if the pulley and shaft turns freely? I detect no difference between the old and new compressor in shaft resistance.

Thanks
Dean

GM Tech on Thu September 20, 2012 8:07 PM

Then why did you replace the "good" compressor- you could have just put a clutch kit on it....never opening the system, no need to replace the dryer...

I'd still get a good look at that TXV inlet screen...

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

mk378 on Thu September 20, 2012 10:42 PM

Also check the flow direction on your new drier. Plumbing a receiver-drier backwards will make it fill up with liquid and starve the TXV(s).

Edited: Thu September 20, 2012 at 10:44 PM by mk378

deandec on Fri September 21, 2012 2:13 AM

Well, GM tech I am just dumb I guess. Thanks for making that point clear. It is such a valuable contribution.

My thought was the 17 year old compressor had done its share and might be the next part to fail? So I elected to spend the $210 to replace the compressor, vs $100 for just a clutch, and a little more to replace the dryer. Those parts cost much less than the $1400 the shops wanted to address the problem. They were not interested in replacing just the clutch. In fact, they were unable/unwilling to confirm that the clutch coil was the problem. I did do so and was correct.

MK378, thank you for the drier flow observation. I think I have it plumbed correctly using the old receiver/drier as a model.

The line from the condenser runs to the "in" side of the drier and the other side exits to the expansion valves and evaporators via a tee line front and back. The old drier has only the N remaining visible and I have assumed that used to be "IN".

It would appear from the responses that neither responder thinks there is still a leak that was not detected by the successful 30 minute vacuum test. So then I will have to open the system to inspect the expansion valve screens or replace the expansion valves.

mk378 on Fri September 21, 2012 11:31 AM

Weighing the amount recovered will tell you if much leaked away. Leaking so bad that it doesn't work minutes after charging would have all the refrigerant gone within a day or so.

A bus job might require more than 5 lbs of refrigerant, the long lines to the front hold a lot. We'll assume the sticker is correct for now, but if you don't find any obvious problems upon opening the system, you could try again and just charge more to see what happens.

Edited: Fri September 21, 2012 at 11:37 AM by mk378

deandec on Fri September 21, 2012 1:25 PM

mk378

Thank you for the excellent added info. I would not have thought of measuring the contents at recovery.

Actually, I am almost 48 hours from the charging process so will measure the pressures to see if they have changed on the high side.

Fortunately, our use of the rig is intermittent so I can play with this problem and try to keep the money I thought I was going to save. I have about $1,000 in cushion yet.

deandec on Sat September 22, 2012 12:51 PM

Well, good news for me.

Evidently the 5 lbs on the sticker is misleading and therefore I just quit too early. Maybe the 17 year old hoses got bigger?

The previously installed pressures held over 48 hours and my search for dye at the connections was non-eventful.

I installed another 1.5 lbs of 134a, and all is good!

Thanks for the help. Great forum.

Dean