a/c relay troubleshoot
 

should one be able to jump the terminals on the compressor relay? Providing 12 v to the central terminal engages the compressor clutch...but there isn't 12 from any of the pins under the relay...is the juice from the control unit? Confused

The power goes from the fuse to the a/c control unit to the a/c relay.

Check for proper charge, the system might be low on charge causing the low pressure switch to open not passing 12V to the clutch.

There could be other problems too. What year is the car?

944 ac
 

It is an '85.5 944. I checked the control unit...seems ok...no matter what I do no juice at the clutch. Pressure switch is bridged. When the central pin of the relay is energized it sends power to the clutch...and th fuse is good.

Do the later cars have an a/c amplifier? The early car does and it's the source that sends power to the compressor clutch.

From the relay power goes directly to the clutch. Are you getting power to the relay from the control unit?

a/c power
 

Hi,
There isn't any power at the relay...it doesn't trip when the switch is thrown and there isn't a hot to jump to the centre pin. The control unit has power...atleast everything else opperates

I'm not savvy enough to load a picture, but if someone can load the schematic here in the form of a picture, I can show you where I'd suspect the problem is.

Hi,
Could you describe it to me ...the contol unit seems fine...just no 12 v at the relay.

On the diagram in the FSM there is a power distribution block for most everything a/c. Right below it in the picture you'll find "Cooling Fan" next to it G10. I assume G10 is hot. Any way from what I traced, the control unit can be hot while the compressor and other related items are not.