recently replaced the evaporator and re-charged the system, every thing worked fine for a while ,now the compressor does not seem to be working. the clutch does not engage when in the a/c or de-frost positions.swaped out relays from another truck and still no life,any ideas?

 

Test the clutch first. Unplug the compressor and run 12V direct to the AC clutch via a couple of jumper wires. The engine does not need to be running. Listen for the click of the clutch engaging. It is not uncommon for these to fail. HTH

 

unplugged the compressor and then turned on a/c,checked the lead going into the comp. with a test light ,no juice.Like I said before all fuses and relays seem to be ok. won't run in the defrost position either,I'm starting to think it is in the control panel in the dash,any body else run across this problem?

 

Does it still have a charge of refrigerant? Could'a sprung a new leak and dumped the charge...
Low pressure (<~28psi) on suction line inhibits clutch operation no matter what..

Beentheredonethat

K.

 

will low refrigerant keep the clutch from operating? I recall back before I replaced the evap. when freon would get low the cutch seemed to cycle more.I did replace the dryer and the system is now empty could this be why it won't engage?But it does not seem to be getting any current to the compressor,is something telling the system not to cycle the clutch(cutting off current to the curcuit) if so I'm thinking I should evacuate the system then give it a charge ,correct?

 

If the system is empty the clutch will not get 12v to engage. There is a pressure switch on the dryer that signals the ecm when pressure is too high or too low.
Pull a vaccuum on it, give it the recommended oil charge, then fill to specs found on the rad support. Usually about 2lbs.

 

low pressure switch, just had to put one on my 95' exploder last weekend. Just went bottom up, put on new switch and worked fine. You can usually jumper the wires at the low pressure switch, just disconnect it and use a piece of wire to connect the two, compressor comes on it's either the switch or you actually have low freon. With gauges installed and your compressor not working I'd say you should be around 90psi on both, and if you jumper the low pressure switch connectors and get the compressor to come on you can watch your pressures. Kinda hard to explain how to know if it's low by watching pressures.