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Can a bad PCM stop my A/C compressor from working?

06 Rubicon

New Member
Joined
May 25, 2022
Messages
1
Location
Anderson, SC
My AC compressor is not turning on, although my system is charged. My mechanic suggested that the PCM might be bad. Has anyone experienced this problem?
 

L J

Ranchos aren't real
Supporting Member
Joined
Nov 26, 2017
Messages
3,982
Location
Dumont Dunes
My AC compressor is not turning on, although my system is charged. My mechanic suggested that the PCM might be bad. Has anyone experienced this problem?
I am by no means an electrical/PCM expert but have you tried using a jumper?
 

tworley

4340 Currie Club
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May 23, 2018
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6,726
Location
Arvada, CO
Your compressor needs a 12V source to cycle. See if you have power going to it.
 

sab

"Semper Discens"
Lifetime Supporting Member
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Jun 12, 2021
Messages
468
Location
DITHOT
The PCM does energize the A/C compressor clutch relay's coil by grounding it based on the dash control switch positions and the A/C pressure switches, so it is possible that it is the problem, but there's a whole lot more to diagnosing it. In order to properly diagnose, I'd start by turning the A/C on, and then check for ~12V on one side of the relay coil and continuity with ground on the other side of the relay coil. If the 12V side isn't 12V, it's something from the fuse to the relay (including wiring harness). If the other side doesn't have continuity to ground, more diagnostics is required to rule out the pressure switches, the compressor, low or high refrigerant, and the PCM. If both sides of the coil are good (one has ~12V and the other is grounded), then your diagnostic lens should be pointed at the power to the A/C clutch (start at the fuse in the PDC and work to the clutch, checking for ~12V the entire way). Here's the wiring diagram for my 2005 LJ Rubicon to show you how the A/C logic works (you can get the full manual for yours from here):

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