My 87 GT got an A/C rebuild when I bought it 2 years ago. The A/C quit working so I checked and it was very low on refrigerant. Didn't have a clue where the leak would be, so figured I could evacuate the system, refill with r134 (yes it was converted before I got the car) and dye to find the leak. I should clarify what work was done when I got the car. New compressor, orifus, dryer, flushed the remainder of the system and replaced all seals and pressure switches. Worked great till now. Anyway, after evacuating and putting in about 16oz. Of 134, it cools a little, but it also cycles on and off about every 5 to 6 seconds. Pressures on the low side cycle from 25 to 45 and on the high side from135 to 95. Any idea why this is happening and what I should do about it. And yes, I did all of the work on the A/c myself and I am not an A/C guy. Worked great the first time. Thanks in advance for the help.
Rapidly turning off and on is called short cycling, and is usually indicative of a system that is low on charge. If you only added 16oz (1 lb) of R-134A after evacuating the system, it is only about hald full, the original R-12 charge is 2.5lbs, and the R-134A charge should be 80-90% of that (or about 2 lbs). The low high side pressures also support this, a there isn't enough gas to compress to build up pressure.
If the low side is only getting down to 25lbs, the pressure cycling switch on the accumulator needs to be adjusted to work with R-134A, it should turn on at 21lbs.
Add another pound of R-134A and see what happens. The system also contains 8oz of oil?
Rapidly turning off and on is called short cycling, and is usually indicative of a system that is low on charge. If you only added 16oz (1 lb) of R-134A after evacuating the system, it is only about hald full, the original R-12 charge is 2.5lbs, and the R-134A charge should be 80-90% of that (or about 2 lbs). The low high side pressures also support this, a there isn't enough gas to compress to build up pressure.
If the low side is only getting down to 25lbs, the pressure cycling switch on the accumulator needs to be adjusted to work with R-134A, it should turn on at 21lbs.
Add another pound of R-134A and see what happens. The system also contains 8oz of oil?
I kinda wondered about the amount of r134a, but it seems that it won't take any more. I've never had a problem adding refrigerant, but in this case it doesn't seem to want to empty the can into the system.
Put the R134a can in a bucket of hot water. Makes it easier to charge the system. High side pressures should be about 2 to 2.2 times the ambient temperature. Too much R134a, or too little, can affect performance. Even 1 oz either way can cause a degrade. Use a thermometer in the center vents, and sneak up on the final charge ( an Oz or two at a time, and then hold and watch them temps). You are looking for around 40 degrees at the vent, or a little better( no lower than 36). If you see the temps starting to go back higher, you might have too much at that point ( check your pressures- too high on the high side means too much R134a). Air flow an also affect this, so make sure the radiator fan is on, and I try and set the idle up to about 1500 rpm while charging.
------------------ '87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)
