SD 455

A/c system works intermittantly. Shuts off at will. Inconsistant operation.
Seems like I can get the system to cycle on if I wiggle/twist the a/c thermostat connector at the evaporator box, behind the glove compartment. Connector seems ok, but suspect, after a lot of other tests,
that the ac thermostat itself is bad. Just to verify, there three wires leading to this component, blk/yel, blu/red, and yel/wht. Can someone give me the voltages of each of these, and can this component be bypassed or "jumped around" temporarily to determine if this is the cause of the intermittant?
Other diagnostics have led me to this point, and the rest of the system checks out. any information is much appreciated.....

edit: Sometimes the a/c will not turn on at all.......then at next startup after sitting, it magically works.
Sometimes it works the whole trip, sometimes not. Never have meter handy when it quits. When the system DOES fire up, it operates normally, inc. condenser fan and normal compressor clutch operation
Once it quits, it seems to ONLY respond to the "wiggle" test at the thermostat, and operation can't be maintaned as soon as I let go of the plug.

SD 455

bump....anyone?

Former User

When the A/C won't work, if you unplug the A/C thermostat and jump the Blu/Wht wire terminal to the Blu/Red wire terminal in the connector, does the A/C now work as long as the wires are jumped?

SD 455

Thank you sir........I have not yet tried that, but the test you're suggesting
is exactly what I was hoping for. Just didn't know which wires to jumper.
I will post my results as soon as possible. Please stand by, and again, THANKS....

SD 455

Ok, tried it today and.............On initial start, blower worked, A/C light illuminated, but condensor fan, relay and compressor were inop. As soon as I grasped the thermostat plug to disconnect it, I heard the compressor clutch engage,and it began to cool. Fumbling with plug made the clutch act irratically until finally I got it disconnected. I jumped the blu/red wire to blu/wht wire at the plug and the system began functioning. It kept operating throughout the first leg of my commute with no issues, same thing on my way home. It's looking like the a/c thermostat is most likely defective, yes?.....And with the wires jumped together, the clutch stays engaged constantly?.....If I need to change the thermostat, is there any short cut or does it require complete removal of the evap. box from the car and opening it to gain proper access?...
Thanks for the assistance so far....Standing by......

SD 455

Probably answered my own question already, but thought I'd post the result.
Haven't had any more issues when bypassing a/c thermostat, other than the air
blowing out the vents is frosty. No doubt because the compressor runs non stop.
Guess I better plan on an r/r of the evap housing and replace the a/c thermostat
to restore proper system operation.

Former User

Yep

In the meantime, you could install a toggle switch between the 2 jumped wires. Then you can accelerate, brake, clutch, and toggle while driving.

SD 455

Yeah, I could do that, but my wife wouldn't like it much
Thanks for the help RonJ