Two A/C Questions (1993 Caprice Classic wagon)

When I bought my '93 Caprice, the A/C was touted as working, and a dealership had converted it to use 134A in place of the original R12. The conversion is somewhat sloppy. At the very least, they reused the original filter/drier. Oh well, it works. If it breaks later or turns out to leak, I'll replace the things that should be replaced. I don't know if they changed any of the seals.

Two questions:

The A/C in the car has never frozen me out. It's "adequate" in 90 degree heat and if that is the way it will be without adding a condenser or doing other work to it, that's fine. Yet I noticed something rather curious after driving on the highway for a while and entering a city driving situation with stop and go traffic. At the lower speeds and when stopped, the A/C system actually cooled better than it did at highway speed. Why might it do this? (Total guess that is probably wrong: refrigerant overcharge?)

I don't have any "hard" temperature data, only the obversation that air coming from the vents felt noticeably (though not majorly) cooler.

It appears that the idler bearing in the (original GM) compressor is going bad. It has a whine that disappears when the compressor clutch cycles on. The same compressor in my brother's pickup truck contracted this same disease and got really, really loud before it all came to an end one day. My factory service manual suggests--if I understand it correctly and can trust my memory--that the clutch and idler bearing can be serviced without removing the compressor from the car and without draining the refrigerant charge from the system, if the right puller is used. Has anyone done this? Are there any hints, tips or potential "gotchas"that I should know about?

The cooling in stop and go traffic will occasionally go into a neutral mode when you are stopped, and it will cycle off, allowing the car to get warmer. Then it will cycle back on when you start to drive again. I am not sure if this is what you are experiencing.

The clutch can be R&Red when on the car, but you do need the puller. From what I have read, it is a lot easier on the bench, but then you have to open the system, which is an offsetting effort. I have not had the joy of doing that repair at this point.

Fred Kiehl wrote:

The cooling in stop and go traffic will occasionally go into a neutral mode when you are stopped, and it will cycle off, allowing the car to get warmer. Then it will cycle back on when you start to drive again. I am not sure if this is what you are experiencing.

It's the opposite. The A/C system cooled better in stop and go traffic (and at lower speeds) than it did at highway speeds (55-70 MPH).

Fred Kiehl wrote:

The clutch can be R&Red when on the car, but you do need the puller. From what I have read, it is a lot easier on the bench, but then you have to open the system, which is an offsetting effort. I have not had the joy of doing that repair at this point.

I know someone who has the puller and will let me borrow it, so that's not a problem. Not having to open the system would be a real plus, as I'm not equipped to pull a vacuum on it and all that good stuff.

Your motion could cause the air column, that the system is producing, to follow a different path when you are at speed, because of the inertia of the air column. It may be blowing on you directly when you stop, and be flowing past you when you are at speed. I have noted that the air from the vents will blow in slightly different directions, when I am turning a corner, vs. going straight.

Check the entire system for partial vacuum leaks. If you have the AC set to max, than the system is drawing most of the air from inside the car. If theres not enough vacuum, than this door may not be closing all the way with the lower vacuum values at highway speed, allowing more outside air in. When you get into the city, the high vacuum at idle will close it completely. You might also check the vacuum resevoir for leaks.

Bill

convert2diesel wrote:

Check the entire system for partial vacuum leaks. If you have the AC set to max, than the system is drawing most of the air from inside the car. If theres not enough vacuum, than this door may not be closing all the way with the lower vacuum values at highway speed, allowing more outside air in. When you get into the city, the high vacuum at idle will close it completely. You might also check the vacuum resevoir for leaks.

Bill

Indeed there is a vacuum leak somewhere. I can hear the hiss of a vacuum releasing and the damper doors moving from somewhere under the dash when I shut the car off. I do have plans to fix this. Out on the highway I was using the Max A/C setting. Yet when I left the highway, I was able to switch to normal A/C and turn the fan speed down. It really seemed that the A/C was working better.

I think it's time to steal borrow my brother's in-vent A/C thermometer, just to see what the temperatures look like.

Well, now I have an explanation why my AC seems to cool better at idle and when braking. Time to go digging for vacuum leaks.