R. Bruno

I have tried everything known to man to get my AC to work correctly. I had a new rebuilt compressor installed about 1 1/2 years ago. It blows cold. The problem is that the belt needs to be unbelievably tight when the compressor is turned on or it will slip and squeal and shred rubber off the belt. I can tighten the belt (with a crow bar tight!) and it will work for a minute or 2 and then again, start to slip. It is as if the compressor is just too tight for the system. When freewheeling, no problems until the AC is turned on. I can turn the compressor by hand, but don't know how hard should it be to turn the black disc on the front of the AC? I have tried numerous belts of various qualities so I doubt this is the problem. How can I tell whether it is the clutch?


[Modified by R. Bruno, 2:35 PM 2/2/2003]

Larry B.

What you are descibing sound like a compressor going out. The black disc one front is the clutch hub and actually is keyed to the compressor and is magnetically locked to the spinng outer ring when you turn the A/C on.. The outer portion is just a free running bearing when the A/C is off. Rebuilt compressors are typically not too good. A new harrison runs about $350 and will work great. I had a 71 that I went through 3 bad compessors from Auto ****. I had one that siezed up and comtaminated the system. $$$$ :cry


[Modified by silvervetteman, 3:52 PM 2/2/2003]

R. Bruno

Thanks silvervetteman. I never had a problem, then the compressor seized. Converted to R-12, rebuilt compressor, evap. etc. $$$ and ever since something is not right., I know some belts are better than others, etc... but there is something weird here.

Larry B.

If you converted to R-134a then it may just be over serviced. It only takes about 60% of the R-12 charge and is very sensitive to the exact correct amout which seems to vary a little. A little over-charge and the head pressure will go too high and that puts a lot odf load on the compressor.

R. Bruno

Thanks again silvervetteman. Yep. I converted to R-134 at the same time as rebuilt compressor etc. Sounds like I need to bring it to another shop. I have done all work on the car myself thus far, except the AC. With AC I am at their mercy however!

Larry B.

When you do... tell them to use ester oil and service to 24-26 psi on the low side assuming the outside temperature of 85-90deg F. My stock 69 aystem with R-134a works great set that way. That equates to about 2 1/2 fourteen oz. cans of R134a. For some reason the older systems seem to like less than the 80% charge commonly used.


[Modified by silvervetteman, 6:36 PM 2/2/2003]

R. Bruno

I just pulled out the repair order and took a look. It say the lo pressure is 25 psi and high is 195 psi. Temp 45 degrees. I am going to get it looked at regardless, but do those sound correct? What exactly do they mean? Thanks for the help by the way. I am an idiot when it comes to AC! :conehead

Larry B.

That sounds perfect. That's about the same as mine. OK here's what it means. The compressor compesses gaseous refrigerant and expells it toward the condenser, (the unit in front of the radiator). That pressure is the head pressure or high side (195 in your paperwork). The condenser does just what the name implies... condenses to a liquid and is sent through a valve at which point it rapidly expands into the evaporator (the unit on the firewall) Rapidly expanding gas gets super cold, and is pulled back into the compressor (the low side) at (25psi which is ideal for R134a) and the process is repeated. the expansion valve and POA valve regulate the low side within certain perameters. The temp reading of 45 deg is the temperature of the air at the dash vents. Too low and the evaporator ices up and impedes airflow through the ducts. Too high and the cooling is inadequate. That's the basics but outside air temp and humidity, airflow across the condenser or a restiction at the expansion valve all play a part in the big picture. Your system may have been reading that when they did the work but something has changed like maybe a clogged expansion valve or an internal compressor problem. A/C is really a simple thing in our cars since we don't have computer controlled stuff to deal with. Actually our compressors don't even cycle like later C-3's do.

R. Bruno

Thanks Silvervetteman. This forum is great. Where else would I get this information? I probably won't get to this for a while, but will post the final results. :cheers:

Larry B.

I just noticed... You are from S.F. ..You don't need A/C there. just good brakes.... :auto:

R. Bruno

Your right about the need, or lack of, for AC here. But, as soon as you get a little north or south.... I could actually care less about the AC. My wife on the otherhand. :nopity
Yes brakes are good to have here in the city but then again, a 4 spd. Vette that measures 15 feet is not exactly the perfect city car anyway. But for cruising down Route 1, Pacific Coast Highway, there is nothing better. :thumbs:

Larry B.

I grew up in So. Cal and lived in San Leandro for a couple of years. I worked at Oakland Airport. I really miss the west coast. Floriduh is thirty five years behind in most things,