DrVincennes

I'm trying to tweak the A/C system on my '72 convertible to get better cooling. I'm using the original compressor, condenser, evaporator, and POA valve (adjusted for R134 as described on this forum); using new hoses, drier, expansion valve. If the foil label on the compressor is original, the compressor is the correct one for my car. It looks like the evaporator housing has never been apart. I removed the resistor/switch on the top of the housing and looked inside with a flash light. The evaporator appears to be bright and shiny with no leaves or debris inside.

I bought the book "Air Conditioning Strategies for the 63-82 Corvette" for the illiterate which has proven to be very helpful. I replaced the plenum door and actuator which was only partially closing and allowing hot air into the A/C ductwork.

A one man local garage who seems to be reasonably knowledgeable of A/C systems flushed the system, added oil and charged with R134. Everything was done following the instructions in the 1972 Service Manual.

On an 80 to 85 degree day, the temperature inside the passenger side vent is about 58-62 degrees at 1500-2000 RPM. This morning at 78* the vent temp was about 56*; however, 2 hours later at about the same ambient temp I could not get below 60*.

Here are my questions:
1. According to the service manual the correct POA valve calibration using R12 is 29.5 PSI at sea level. Various forum threads call for 27-28 PSI using R134. Is there a way to check the actual PSI while the valve is installed and the system charged or must the valve be removed for testing?
2. After running the AC for only 10 to 15 minutes, the compressor begins to sweat. Is this normal?

Any information and input would be appreciated.

Dr

MelWff

1. I'm not an A/C expert but would the 27-28 PSI reading be the same as the low side reading which a set of gauges would tell you?
2. Any cold surface will sweat if the humidity is high, dont see anything abnormal with that.

DUB

I do hope that when you put the 134 Freon in...you reduced the amount as required. When using 134 in a R12 system...you do not but the same amount in the system. The A/C shop who charges systems for me puts in 80% of the normal volume required.

I have seen the evaporator core sweat...but not the compressor itself.

You need to drive the car and hopefully the fan clutch is good. The more air you can get to flow across your condenser ...the better. IF on MAX on the A/C controls...it will recirculate cold air and the temp will being to drop further...and that is if the outside air door baffle is doing its job....along with the door in your passenger hinge post/kick panel area has to be open.

DUB

DrVincennes

Thanks for responding guys. Yes, the amount of R134 installed was 90% of the R12 system capacity. I did replace the passenger side kick panel door seal and vacuum actuator. The kick panel vent and plenum door now operate as the manual prescribes. Today I talked to a long time mechanic at the Buick garage who said the compressor should not be sweating. The mechanic who owns the shop who charged my system said the sweating compressor was normal. One must be a liberal; the other a conservative.

Dr

SIXFOOTER

I have seen a lot of things sweat, but never a compressor. Your applying energy to a compressor and it is compressing the gas/liquid mix which generates heat. The compressor and condenser should get Hot and the cold sweaty part should be the evaporator.
Not much help as to why, don't know if the reduction of volume of only 10% is the cause, I was under the impression that 70% to 80% was the right range.

chevymans 77

The compressor sweating can be caused by a few things, overcharged, low cabin air flow, partially plugged evaporator. Looking in from the blower resister hole will not tell you much as the air flow inlet is from the other side. Compressing 134a generates more heat and is why cars designed for its use have cross flow condensers. You may consider one for your car if you truely want all it can do. Staying with the VIR is the best option for the lowest vent temps. You should see lower temps than your seeing if everything is working correctly as it is.

Neal

Jud Chapin

Take a look at the weatherstrip piece on the rear of the hood, assuming it's still there. If it's not sealing, you're sucking hot engine compartment air into the cabin. If it were me, I'd just replace it. One way to tell if it is leaking though is to have the system on out side vent, a/c off with a thermometer in the center vent. The temp should be that of outside air. Before I replaced this strip on my '76, the temp was about 90 degrees at the vent. After the strip was replaced, it dropped to that of outside air. More importantly, the vent temp with a/c on went from the high 40's to 40 degrees, and I live in S.Fla.

However, while this fix will help if needed, you've got something else going on with 60 degrees at the vent. I run R12 and have never been a proponent of switching to R134a. These cars were built for R12 and, contrary to popular opinion, it's not that much more expensive than its counter part. Check Ebay prices. And FWIW, I though when switching to 134, it's recommended to use a larger condenser.

I'd also have a FULL look at the evaporator. You can only see one side with the way you are looking at it. How is the air flow from the vents?

mrvette

My '72 is a rag top, so long ago I sealed the plenum hatch closed, and disconnected the valve and vac lines, removed the door to the kick panel area, so the car is on permanent recirculate.....I also have 134 with adjusted POA valve in place, but using a 88-91 vette compressor with same serp drive.....and custom hoses, of course....I put just enough 134 in there to get 50f out of the vents on a hot 100f high FLORIDA humidity type day.....obviously I vacuumed out the pressure side of the evap coil, and that is critical, bet it's full of leaves in there, I cheated though, cut out the fender well liner behind the wheel, and removed the blower motor the easy way, and ran my shop vac in there with a small hose, plenty of suction.....replaced the OEM blower assy with a C4 blower/fan assy, and made a 3/4 inch spacer for the motor mounting flange, giving much higher airflow......

IMO, before second guessing anything, I would just cut that fender liner, remove/replace the motor, and suck that coil out, take your shop mirror and a small flashlight to see for sure that it's CLEAN.....


OH, on that fender liner....I just got a piece of sheet vinyl from Lowes Despot cut to size, and shoved a few sheetrock screws into the plastic painted it black and no one can tell the diff unless they look really close.....