pantera928

Here is an enigma for you. I have voltage through the pressure switch and up to the connector near the right front fender but the compressor clutch will not engage. If I pull 12VDC from the tap near this connector, the clutch engages. If I check the voltage at the low pressure switch and at the connector, all looks good but the clutch appears to pull the voltage down to zero once the clutch tries to engage. It appears that while the voltage is available, there is not enough current passing through to engage the clutch. Voltage only shows if I disconnect the clutch from the circuit. Any ideas????

The Forgotten On

Possible failed relay in the head unit maybe?

996Fever

Yep. Sounds like the relay in the controller. Just went through that earlier this year. Relay under rated the day it was installed by Behr or Porsche, whichever you choose to blame. Burns out and will pass voltage but not current. Installed the external beefier relay per Dwayne's write up. Cost me a total of $12. All good now. Read Dwayne's write up at the link below Pantera and you will be fixed in no time.

https://rennlist.com/forums/928/6788...re-w-pics.html

dr bob

Need a little clarification on how you tested and your results.

-- What Year Is Your Car?

-- Test for voltage and voltage drop with everything still connected, all the way to the compressor clutch connection in the front of engine harness.

-- Current flows through the mini relay in the head unit through the CE panel, freeze switch under the cowl cover, pressure safety switch, 14-pin connector, front-of-engine harness, to the compressor clutch connector pigtail by the oil dipstick tube. Work your way from the freeze switch connections, the pressure switch and the 14-pin since those can be accessed with everything still connected. Testing at the pressure switch may require that you build a couple short male-to-female pigtails so you can connect your meter. Use one of those then to test at the compressor pigtail.

-- With everything connected and turned on, if you see low voltage at both of the freeze switch connections it's most likely the mini relay in the head unit. Confirm by disconnecting the compressor to see that voltage comes up at the freeze switch. If you don't see these exact results, your problem is not the relay.

pantera928

Thanks for the responses. I thought the head unit in the console was acting flaky anyway so I replaced it with another I has and all is working. Now to tear apart the one I took out and possibly do the relay modification.
Thanks again

pantera928

Thanks for the responses. I thought the head unit in the console was acting flaky anyway so I replaced it with another I has and all is working. Now to tear apart the one I took out and possibly do the relay modification.
Thanks again

docmirror

AC clutch relay in the HVAC head is a very high failure rate. It's almost sure to need upgrading. There are several threads on how-to.