1999 Blazer 4WD 4.3L
A/C compressor is not kicking on at all. All fuses in the fuse panel and all relays in the fuse center are good. Blwer works, just blows warm air. Any troubleshooting hints would be very welcome...

 

Low side pressure must be at least 42psi for the compressor clutch to engage. There is a pressure switch in the accumulator, (large aluminum can) near the passenger side firewall. There are two wires in the connector, unplug it and check the resistance between the two pins in the switch, must be less than 5 ohms. Post your results.

 

You probably have a leak in your system. Buy a can of r134a with dye in it, put it in on the low side service port and check for leaks. The compressor won't turn on if its out of refrigerant.

 

Low Freon, Faulty Pressure Switch or Faulty Clutch. You can test the pressure switch by disconnecting the plug and jumping the two pins together in the plug. The clutch should engage. If the cluctch engages you know the switch and the clutch is good and most likely low on freon. You can also apply 12v directly to the clutch to test the clutch.

 

You guys hit the nail on the head. It was the switch. I shorted it out, the clutch kicked on. Changed the switch, refilled with R134A with sealant and we're cooling again. Also noticed some leakage where the tubes enter the compressor so if it leaks out again I will disconnect and replace those o-rings at that time. Great job guys and thank you all very much !

 

Glad you got it fixed. Nothin worse than hopin in your truck on a hot day and havin no air lol.

 

Did you pull a vacumn prior to recharging?

 

yea, if the system had discharged you should put it on a vacuum at 29inches for at least and hour to remove any moisture in the system prior to recharging with freon. otherwise it will work, just not as good. as to adding sealant to the system... I would just locate the leaks and repair them. I have an issue with adding sealant to a system... Never know what small things it is going to decide to seal. (Pressure switches come to mind)

 

All,

Similiar problem to this thread, but jumpering pressure switch did NOT make ours come on. (2000 Jimmy SLE). We managed to run a wire direct from battery to clutch-on-compressor connector and clutch engaged. Fuses/relays seem OK, at least the ones we found.

Suggestions? (Trying to fix for college girl home for Easter.)

Thanks!

Happy Easter to all.

Mark

 

See post #2 for some preliminary tests. Also need to check the high pressure cut out switch on the rear of the compressor. It disables the clutch if pressure is too high, but it can fail and keep the clutch from engaging as well.