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Eric, Automotive Repair Shop Manager
Category: Toyota
Satisfied Customers: 32564
Experience:  20+ yrs. experience as repair shop manager and technician.
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Toyota Corolla CE: A/c compressor not running. Whyever not

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A/c compressor not running. Whyever not?

what year corolla is yours?
Customer: replied 4 years ago.

2004 - didn't that show up? I selected it.


for some reason it didnt show it on my side.

Ok, the pressure switch is on the right side of the engine compartment





Customer: replied 4 years ago.

Eric, OK, found the switch. Is there any other reason for the compressor clutch not to get power? The refrigerant pressures are OK and the in-cabin 10A fuse is good. (The switch is over $200., and the dealer doesn't have it in stock.)


yes, there are other reasons. no signal from climate control panel, no signal from the ecm to the compressor clutch relay. But the most common is the switch.

Below is testing for the switch. If it test good, let me know and we will go from there:

Customer: replied 4 years ago.

This is interesting - there is continuity between terminals 1 and 4 in the range indicated, but the pressure doesn't get to the range, below 28psi/above 455psi, that should open the switch. Plugging the connecter in makes the fan operate, but not the clutch. Maybe an open circuit between the switch and the clutch? Should I make a jumper connection between the switch and the wire to the clutch near the clutch? But wait, late breaking discovery - no power to either 1 or 4 at the switch. Which one should be powered, and from where?


Ok, terminal #1 goes to the ECM and sends signal to it

Terminal #4 is ground and is opened and closed by climate control panel.

it sounds like either no signal between the switch and the ecm, or none from ecm to clutch relay.

Customer: replied 4 years ago.

This is a cycling compressor, not a variable displacement one, is it? (Thinking of borrowing power from the fan control part of the switch - that might indicate whether the grounding function is working - if it didn't blow up while testing.

The control panel A/C light comes on on demand, if that tells us anything.


Where do I go from here?


yes, it is a cycling compressor

have you tried a jumper wire between terminal 1 and 4 on the switch connector? try this to rule out the switch. If the compressor runs, then replace the switch.

If no go, then run a jumper from pin #1 to connector A pin #13 on the ecm and see if it runs.

If no go, then check for power out at connector C pin #2(yellow/black wire) on the ecm.

If power, then check for 12v on pin #2 on ac clutch relay. If no power, then repair short in the yellow/black wire from ecm to relay or just replace that wire.

Customer: replied 4 years ago.

Excellent. "I'm on it!"


ok, let me know how it goes
Customer: replied 4 years ago.

Eric, jumping 1 and 4 makes the compressor cycle, but it pumps for just a couple seconds and kicks out, so doesn't make cold air. Switch, for sure? (Rock Auto lists them for under $20.)


Yes, definitely the switch. with the connector jumpered, there is signal to the ecm and from ecm to relay and relay to the compressor. Replace the switch and it will be good to go
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Customer: replied 4 years ago.

You were right - again. Cold air all over the place. Too bad Toyota couldn't have afforded a little valve to enable the switch to be changed without evacuating/recharging. But ohhh, no. They saved a quarter of a cent per vehicle. Legendary something.


always glad to help.

i agree, and most due have the switch screwed onto a port with a shrader valve inside it to prevent having to evacuate the system.
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