AC compressor clutch will not pull in

Tiny
DKEEN
  • MEMBER
  • 2001 OLDSMOBILE ALERO
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 220,000 MILES
Checked Freon and pressures good, if I pull relay and jump terminals 30 to 87 compressor will run and cool down, the switch on panel is on for AC and the fan switch is on. The system seems good but electrically not so sure of. It has three wire switch on high side line cannot find low side.
Wednesday, June 13th, 2018 AT 6:55 AM

28 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon.

Did you check for two powers at the relay? 30 should have voltage and 86 should have voltage.

There is only one pressure switch. You need to verify 5 volt reference signal from the switch.

Roy
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Wednesday, June 13th, 2018 AT 4:07 PM
Tiny
DKEEN
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I checked and had both voltages at relay and had 5 volts at pressure switch.
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Thursday, June 14th, 2018 AT 4:11 PM
Tiny
DKEEN
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Have changed relay.
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Thursday, June 14th, 2018 AT 4:13 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, the PCM is what grounds the control side of the relay when it gets the correct signal from the pressure switch.

You have a 5 volt reference, a ground and a signal wire that go from the pressure switch back to the PCM.

What are the pressures in the system?

Roy
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Thursday, June 14th, 2018 AT 4:30 PM
Tiny
DKEEN
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35 and 135.
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Thursday, June 14th, 2018 AT 5:13 PM
Tiny
DKEEN
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With jumper in, sorry.
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Thursday, June 14th, 2018 AT 5:14 PM
Tiny
DKEEN
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85 low side and 35 high side jumper out not running.
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Thursday, June 14th, 2018 AT 5:20 PM
Tiny
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High side went to 45.
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Thursday, June 14th, 2018 AT 5:21 PM
Tiny
DKEEN
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High side slowly climbing at 55.
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Thursday, June 14th, 2018 AT 5:25 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, the 35 and 135 are not bad.

You will need to check that transducer or switch.

Back probe the switch. You should have 5 volts on the feed, one is ground and the other is the signal. Can you tell me the voltage on the signal wire?

Roy
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Thursday, June 14th, 2018 AT 5:29 PM
Tiny
DKEEN
  • MEMBER
  • 18 POSTS
3.2 volts.
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Thursday, June 14th, 2018 AT 5:41 PM
Tiny
DKEEN
  • MEMBER
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Correction 4.6 did not have a good connection.
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Thursday, June 14th, 2018 AT 5:42 PM
Tiny
ASEMASTER6371
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What color wire?

If that is the signal wire, that should be good enough to ground the relay and turn on the compressor.

Roy
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Thursday, June 14th, 2018 AT 5:43 PM
Tiny
DKEEN
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Red and black - red wire is the signal.
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Thursday, June 14th, 2018 AT 5:45 PM
Tiny
DKEEN
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Sorry, grey wire is 5 volts.
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Thursday, June 14th, 2018 AT 5:46 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay.

You need to check the wire at the PCM next. Check the diagram and go to the connector and pin number. Back probe the wire for the relay control. See if there is any voltage there with it hooked up to the PCM.

Roy
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Thursday, June 14th, 2018 AT 5:58 PM
Tiny
DKEEN
  • MEMBER
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I checked conductivity on both wires red-signal and the black ground from the pressure switch connector back to the PCM connector and they checked good. Could not get on connector to check the voltage with it plugged in.
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Thursday, June 14th, 2018 AT 6:51 PM
Tiny
ASEMASTER6371
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Okay, you need to check the wire from the relay to the PCM. It is the dark green/white wire from the relay to the PCM. You need to see if there is voltage at that wire at the connector.

With the plug removed you should have voltage and when you plug it in, it should not have voltage.

Roy
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Friday, June 15th, 2018 AT 2:49 AM
Tiny
DKEEN
  • MEMBER
  • 18 POSTS
I pulled the relay and probed the coil side of the relay in the base of the connector and I had power with relay out twelve volts, I reinstalled the relay and had some jumpers in with relay prongs and when I plugged the relay back in I lost power to the coil side of the relay. The voltage I had was twelve volts. I am assuming there is a triac output in the PCM is the reason for this?
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Monday, June 18th, 2018 AT 4:17 AM
Tiny
ASEMASTER6371
  • MECHANIC
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The control side power is controlled by a fuse from the fuse block. The ground for the control side is controlled by the PCM and that is based on the signal from the pressure switch.

If the dark green/white wire has voltage, then it is not being commanded to ground. It should 0 volts if it is grounded.

Do you have a scan tool to monitor the operation of the AC commands?

Roy
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Monday, June 18th, 2018 AT 4:24 AM

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