Need help with repairing 77' Airstream RV engine AC

[ArgosyRV]

Hello, I have a 1977 Airstream RV on a Chevrolet P30 Chassis. It had original dash ac.when I bought the rv the AC was not functioning and the pump seized and threw the belt the first time I drove it.

I have replaced a few Ac systems in the past and I am a competent mechanic, but not a lot of AC knowledge beyond basic theory and function of parts.

I replaced the Frigidaire A6 pump (reman), condenser, drier and all new lines.

Flushed the original sealed evaporator until flush ran clear.

I was unable to locate an expansion valve or an orifice tube.( it must be inside the sealed evaporator box that I cannot remove without removing the dash) during flushing there was restriction so it has one or the other.

I added 6.5oz pag oil to the 3.5oz of unknown oil that shipped in the pump and 48oz of A134 per capacity sticker on the vehicle.

System performed flawlessly, in 85 degree 80% humidity in Florida I was getting 42 degrees on high at the vents.

After about 400 miles of driving with the ac on over a number of trips, the pump began to squeal in traffic and threw the belt. after the RV cooled down I reinstalled the belt and the AC blew cold again. After 30 min it seized again and I quickly turned it off.

Now when the engine is cold it will still function for about thirty minutes before it seizes again.

(engine cold) Static pressure is perfect according to the ac chart and under hood temps (88 degrees/101psi) . with the ac running engine at temp in 90 degree heat idling for 10 minutes low side is at 27psi and high side is at 192psi 44 degrees at vents. its hard to get a reading but when it starts squealing I have seen it spike to 275 on the high side before I quickly shut it off before the belt starts smoking.


Im not sure where to start? bad remanufactured compressor? bad or no cycling switch? non compatible oils? overcharged?

I don't want to just throw parts at it without a plan. Any idea what would cause this?

Thank you,
Bill

[tbirdtbird]

"I added 6.5oz pag oil to the 3.5oz of unknown oil that shipped in the pump and 48oz of A134 per capacity sticker on the vehicle."

I would have drained/removed all the oil that came with the reman A6 since it was unknown, and used ester oil (not PAG). If the old oil was mineral oil as would have been used with R12, then any trace amounts left over after you drained all the oil (whatever it was) would have mixed OK with the ester oil.

If the A6 is seizing, it is because there is a lubrication problem. A hi side of 275 is not high enough to stop it

It might not be too late to save it, but I would be concerned that metal particles have been sent down the line to clog the condenser

[ArgosyRV]

Understood, that was my fear as well.
does this it sound like a best case way forward?

- flush entire system, each component separately to remove all oils
- replace drier
- replace pump, drain shipping oil
- add 10oz of POE oil?
- recharge

thank you

[tbirdtbird]

I suggest letting one of our other consultants (JohnHere) chime in since he is more familiar with the A6 than I

[ArgosyRV]

Also, I am planning on installing the new replacement S6 compressor that apparently has an updated Sanden style pump inside and is designed for a134? also I plan on adding a secondary thermostatic cycling switch as I do not believe the pump is cycling with the original setup. is this replacement considered good quality? The tech at Oldair spoke highly of it. Does anyone here have experience with it?

thank you

[tbirdtbird]

I personally have had miserable experience with the S6. Also with the ProTen6 that came before it, which has been discontinued.
If you decide to go with the S6, Tim here at ackits.com can get you a waay better price than OldAir

[tony1963]

If you couldn't find an orifice tube, then there must be an expansion device somewhere.

Also, is this a single evaporator system or a dual evaporator system (front and rear)?

[ArgosyRV]

Single large 6 vent Evaporator under dash. basic o-ring style #6 in and #8 hose out.

[tony1963]

Recover the charge and open the system. Pour the oil out of the accumulator and see if it is clean or full of debris.

If full of debris, you toasted the compressor and need to start over and flush the system, install new parts. Add the proper amount of oil.

If not full of debris and clean, then your compressor may be developing high pressure and cannot overcome the force. However, I'd expect that you would vent refrigerant before that happened. The reason I bring this up was I had a Volvo 960 once that performed well but at idle the clutch slipped. We determined that the fan would stop running due to a bad relay that couldn't keep it engaged long enough, thus, the pressured increased when the can cut out. It never vented refrigerant and it never stopped from the high pressure cutout.

[ArgosyRV]

"Recover the charge and open the system. Pour the oil out of the accumulator and see if it is clean or full of debris."

my system does not have an accumulator it has a drier mounted on the condenser. same procedure?


Interesting what you said about pressure, that was my first thought as well. But, being that it worked correctly for 400 miles wouldn't that disprove that? I have been torn between lack of lubrication and hydraulic-ing the compressor but did not want to lead the conversation? (also with the very high under dash temp in an RV with a 454 big block and a pump mounted 2" from the exhaust manifold I find it unlikely that liquid refrigerant is making back to the pump? or is my thinking incorect?)

just an FYI it has a very large condenser and the output is at ambient temp when the problem occurs. I originally suspected it may need a fan, as I have had other systems overheat the condenser due to lack of cooling and bog the compressor.

I found an older thread where Tim from ackits.com seems to suggest the new Alma A6 pump is superior to the S6 pump due to higher bore capacity and similar price? Is this still the best A6 replacement?