Need air con help on truck

Just replaced the air compressor dryer and orifice tube on 99 GMC pickup. Pulled vacuum and charged system. Low side running about 50 high side running about 210.  clutch is make funny noise engaging and disengaging chatter of some sort. While charging it almost sounded like compressor would let off air pressure. I know the clutch will self destruct the way it is acting. Please help me fix it, I am at wits end. Thanks Tracy

X2

We didn't put as much as was recommended, stop short of that. Can't figure why low side is that high. I wondered if there could be a restriction somewhere. Still don't know why new compressor has a clutch that is not working right. Maybe a seasoned mechanic will chime in, and tell me what to look for. Thanks Tracy

As Joe says,both numbers are too high which means there is too much in there. I don't know what book calls for (lbs of refridgerant) but if you have the big bottle,you can use a bathroom scale to weigh it in and get real close after vacuumed out. Otherwise do the math on the cans...

Edited by SteveM C/IL - 27 May 2019 at 12:47am

First question, when charging did you put it in as a liquid and on the high or low side? Dumping liquid in the low side will damage the valves. You said you vacuumed it but air in the system will act as you described. I like to pressurize the system to 115 to 119psi of nitrogen for 30 minutes first. That lets you check for leaks and pick up any moisture in the system before you evacuate.
At 210, your clutch should not be cycling on high pressure.

lot of good info here and some not so good info. the system should be flushed any time it is opened up. and the filter/dryer replaced. In addition, if the system is being worked on because of replacing a burned out compressor, you really should replace the condenser too. just too hard to get all the crap out of it from a compressor failure.


I know lots of guys charge a system by pressure only, but that is not the best way to do so. One can likely get in the ball park buy adding gas to a target value on the high side, but those pressures vary with ambient temp. You can get 'close enough' by charging by weight, but the best way to charge is pressure adjusted for temp at the condenser, but you need a handy dandy conversion chart for the specific refrigerant being used.


probably the best way to charge for the home mechanic is by weight, but you need a baby scale, or similar, maybe a postage scale to do so, since we are only using a few ounces. A bathroom scale wont cut it. weigh the can before and after.
one last thought, deliberately venting refrigerant into the air is a federal violation. I'm sure it is done, but in this treehugger mentality society, I sure wouldn't go around talking about it

the exception is that little bit of gas lost in connecting or disconnecting gages to the system

210 on the high side is high but not out of line for a 99. They started 134 in 95 from R12. Took them 10 years to really figure it out. High pressure cutout is somewhere around 300-375 there abouts. Low pressure cutout will be around 20-25. I'm assuming it is still cycling the compressor as it is right now. Jump the switch on the accumulator 'low pressure switch on the can' with a paper clip and let it run and see what it does. If it eats the compressor take it back and get another. May have been junk to begin with. Never know what you get anymore no matter what you pay.

99 didn't use R12. 134 was started in 95.

Tracy! What did you decide? Follow up please!

It is running and cooling . Pressure is higher than should be. Going to see if a HVAC mechanic can figure out what is causing pressure. It was cooling down to 40's traveling on highway. Thanks Tracy