How many volts at the A/C Compressor?

Tim Groth

SCCoA Member
Trying to button up a few of the last items on my 1995 SC, that weren't finished before the Hot Rod Power Tour. AC components were added back to this car after running with the systems fully removed for 3 years. Wife won't ride with me till they work, so trying to get systems on board.

AC System new components are:

New OE Condensor
New Lines - Both
New Accumulator Dryer


Used but considered good parts:

A/C Compressor - clutch engages if powered directly from Battery w/ pigtail
Low pressure switch also called A/C Cycle switch in the service manuals - no change in systems if paper clip is used to bypass.
High Pressure Switch on return line - no idea.

On the power tour we tried to add freon without luck. At that time we discovered 0 voltage at the compressor also the condensor fan does not kick on with A/C. We were told IRCM as the culprit...I keep a spare in the glove box so that was changed out.

I now have 8.8v at the compressor but it does not engage. If I manually engage the compressor with a pigtail to the battery it pulls the clutch in and runs.

At this point my questions is first could someone who has AC tell me what voltage they have at the compressor? Should it really take 12 full volts to engage the clutch? Could I still have a bad IRCM? ...I have another spare I could try (figured I'd ask first).

Stumped as to were to look next.

-Tim
 
If you can wait until Monday evening after I bring my Volt Ohm meter home from work I'm happy to check. I have a 94 SC with working A/C.

One quick question - Where are you applying 12V? Right at C107?

54-3 AC snippet.JPG
 
Last edited:
Check the ground.

It SHOULD be 12V more or less (by "more or less" I mean the system voltage isn't exactly 12V).

Exact wiring varied from year to year, alas; my 1990 and 1993 EVTMs show different wiring for the non-EATC units. The 1990 doesn't show the EATC.

My 1991 is "busy" at the moment (fancy for "It's in the pile on the bench, can't be arsed to double check there.")

RwP
 
20180714_103555.jpg

Yes right at c107 I have 8.8 ...picture should show how i just have a pigtail wired directly to the battery to make it engage...testing purposes obviously.

Also waiting till Monday is fine. This car is just drove for ice cream on Friday nights. No rush, and appreciate the help.

-Tim
 
Last edited:
8.8v is your problem, and if you confirmed that reading direct from the connector to the battery, grounds aren't your issue. If ground was an issue, I'd expect other symptoms.

A/C Clutch eventually grounds at G100, which is left hand side of IP, near steering column...meaning it grounds thru the switch, via the IRCM. However, it looks like there is a diode in the circuit between the IRCM and the clutch "taped to engine harness, near A/C clutch coil connector, 5.1" from A/C clutch coil".
 
Back
Top