A/C wiring problem-voltage drop

[slowstang]

Hey guys. Out of nowhere, my A/C compressor and A/C clutch quit getting power when the A/C is turned on. So I checked the two silver relays that control them (in fuse box close to driver side firewall). I found the problem to be that the voltage across the two pins that switch the relays on is only 9.5volts which is not enough to flip the relay switch. I checked the relays at 12volts in another slot (radiator fan slot) and they both worked fine. Likewise if I use a jumper wire to simulate the relay both the AC fan and clutch will work. What could have happened that all of the sudden the voltage going to that relay would drop by ~3volts?

 

[theSicKness]

there is resistance in the wire some where.. could be corrosion some where.. i would never use a jumper wire.. id try tracing the wires....



my .02

Jesse

 

[Freerevving]

maybe your pressure dropped... or your pressure switch is broken... very common

 

[slowstang]

Well I fixed the problem and the AC is working great now. I replaced the small AC control unit that Defiant talks about in half of these AC problem posts. They dont make them anymore so I had pull one out of a friends parts car.

For anyone that has the same problem, if you look at the wiring diagram, the fact that the AC fan is not coming on when the AC switch is pushed is the big hint that it's not a typical problem (as long as all your connections and relays check out). That fan comes on regardless since the hi/low pressure switch only controls the compressor itself. That control unit controls the power to the AC fan, compressor, and even tells the fans when to switch from hi/low speed, so if your having any problems getting voltage for any of those situations, check the control box. Mine had a burnt transistor. The control box is located on top of the evaporator directly behind the glove box. Hope this helps.