A/C compressor bad?

[sCarycary]

So I got to troubleshooting why the dash air blows warm. The A/C compressor never clicks on. I checked and it is getting +12VDC when I select the A/C function on the dash control. I hooked up my HF(Harbor Freight) A/C manifold gauges and the low side is right where it should be at 40psi. The high side is of course at the same since the compressor doesn't turn ON. I'm going to the Rock Auto Parts site and see if I can determine which compressor to order. Oh, I have a 1999 Rexhall on the the Ford chassis. I believe we call that the F53. I think some of the F550 parts are interchanceble too. Anybody ever change their own A/C compressor before? Wish me luck.

sCary

[sc3283]

Are you sure your clutch is getting +12vdc?

You can just replace the clutch...you do not have to replace the whole compressor for just a clutch failure

[ga traveler]

Your static pressure is too low to turn on the pressure switch. You have a pressure switch that will not supply 12v to the compressor if the freon is too low. you DO NOT have a compressor problem. Add freon until the switch comes on or jumper out the switch to add freon. Of course hook up the switch again when the pressure comes up.

[melvonnar]

Before you order a compressor try adding a can of freon to your system;low freon charge and compressor will not start.
Gee some one already said that. sorry for the repeat.

[ga traveler]

I just went back to my A/C course book. It takes 45 to 50 psi to turn on your switch. You don't have a compressor problem, as i said before. Your compressor just will not switch on at 40 psi.

[sc3283]

Not all low pressure switches are calibrated with same pressure cut in and cut out rates. The system in question may not even have a low pressure switch.

OP if you can find the low pressure switch, jumper the 2 wires and then recheck the AC clutch for voltage..........that is if you had no voltage at the clutch originally.

Just going and randomly adding freon in hope to fix an electrical problem is a BAD way of diagnosis. We have NO clue the ambient outside temp where the vehicle is parked. if ambient temps are low enough...40 psi could be perfectly normal..
if this would be the case, then the system could be 1 can overcharged on freon

[ga traveler]

Originally Posted by sc3283

Not all low pressure switches are calibrated with same pressure cut in and cut out rates. The system in question may not even have a low pressure switch.

OP if you can find the low pressure switch, jumper the 2 wires and then recheck the AC clutch for voltage..........that is if you had no voltage at the clutch originally.

Just going and randomly adding freon in hope to fix an electrical problem is a BAD way of diagnosis. We have NO clue the ambient outside temp where the vehicle is parked. if ambient temps are low enough...40 psi could be perfectly normal..
if this would be the case, then the system could be 1 can overcharged on freon

#1 looked at his profile. It is a 1999. All 1999's have a pressure switch. #2 I looked at his hometown It san jose california. Not known for being freezing. I have been to school on A/C and have been taught that 40 psi and below will not turn on the compressor. If I had not had the information he supplied, I would NEVER have just said add freon!

[Triker56]

Hummmm! My compressor will run when low as 15 PSI blowing warm-cool air and after adding 2-3 cans of 134. It will get up to 30-35 PSI and is putting out a lot of cold air.
By the outside temp of around 70º plus, 30-35 PSI is enough by the cheap Walmart gauge. Anywhere between 25-45 is good over 45 is too much.

[mfire1339]

The low pressure switch is on the "high side".


Mike

[sc3283]

sCarycary, back to your original question....if you do need to change your compressor, it is just simple mechanical skills required to replace..BUT>>>>

you do have freon in the system, so by law that has to be recovered. The days of just letting it be released into the atmosphere are gone(legally, if you catch my drift).

You will have to evacuate the system(draw a vacuum on the sealed system) after replacing the compressor, then recharge with proper amount of refrigerant(freon).

The REAL bad news is though....if your compressor has failed and failed to the point it actually blew up internally, you have an extreme chance of total system contamination(various parts and pieces of the compressor, throughout the sealed system). Keep your fingers crossed this has not occurred as this is now a really expensive repair.

Remember shooting from the hip for diagnosis can end up costing you a ton of extra time and money. It is always best to diagnose properly first, then properly repair 2nd

[KIX]

Originally Posted by sCarycary

The A/C compressor never clicks on. I checked and it is getting +12VDC when I select the A/C function on the dash control.
sCary

Assuming the OP is checking and found 12vdc at the clutch on the compressor it should have "clicked on". Unless..........the compressor is seized and then the belt would probably be broken. So, my diagnosis is replace the clutch if after removing the old clutch the compressor shaft spins freely.

[ga traveler]

Originally Posted by Triker56

Hummmm! My compressor will run when low as 15 PSI blowing warm-cool air and after adding 2-3 cans of 134. It will get up to 30-35 PSI and is putting out a lot of cold air.
By the outside temp of around 70º plus, 30-35 PSI is enough by the cheap Walmart gauge. Anywhere between 25-45 is good over 45 is too much.

You are right. If you go over 45 psi on the low side, you will be over serviced. However we are talking static pressure. That is the pressure on both sides when the compressor is shut off. The switch is on the HIGH side. I state again you need 45 to 50 psi to make the switch work. I was only trying to save the guy from buying a compressor. I am not there to do a correct eval. of his system, which is the only way to correctly diag. the problem.

[tkolbe]

FYI,
You can check the pressure switch without anything running. Just disconnect the two wires from the pressure switch and check for continuity across the switch using a volt ohm meter. If you have continuity, then the switch is closed, you have enough static pressure, and the compressor should run. This does not mean that the system is not low on charge and could still trip the switch after running.

[DesertRhino]

Seems most of the posters are on track.

45# static pressure is too low. That is the definite first thing that should be checked prior to any other troubleshooting.