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99 Explorer A/C Clutch will not engage

bitterdog

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April 7, 2008
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Year, Model & Trim Level
99 explorer limited 4.0 s
Good Afternoon.

I have a 99 explorer where my A/C clutch wont engage.

If I jump the a/c relay pin 85 to pin 87a it will engage.
If I jump the a/c relay pin 86 to pin 87a will NOT engage.
If I jump pin 30 to 87a it will engage.
Swapped out the relay - no go

I jumpered the low side pressure switch - no go
I checked the low side harness for continuity and Voltage 13.8v
I assume the red/white striped wire is from the EATC? There is no power from it.
The black/white wire read 13.8v



I jumpered the high side switch - no go
I checked the high side harness for continuity and Voltage 13.8v also

I then Jumpered the high side harness and low side harness and still no clutch engaged.


All fuses checked.

Refrigerant levels read good when I jump the relay and turn on the compressor

Did a EATC self test - only code was for a bad blend door.

I don't know what else to check. I would greatly appreciate any other suggestions besides take it to the shop I live in Arizona and it will be 100 degrees this weekend.

Feels like I'm getting close to leaning towards the PCM


35in2oh.jpg
 






Looking at the wiring diagram, that you can jump the clutch relay at pins 30 and 87a and get power to the a/c clutch does very strongly suggest the PCM is what/where the problem lies.

The PCM has a couple specific reasons it'll turn off the A/C -- either an engine over heat, or at Wide Open Throttle.

An OBDII data reader might show the engine temp sensor is whacked out and the PCM thinks it's in over heat.

I'd suspect if the throttle position sensor had whacked out, you'd get a bunch of check engine fault codes.

One thing to check. With the engine off, key out of the ignition, do you have power to pin 30 on the relay? If not, a "semi permanent" jumper between pins 30 and 87a should bypass the PCM's control and get your A/C running.
 






Looking at the wiring diagram, that you can jump the clutch relay at pins 30 and 87a and get power to the a/c clutch does very strongly suggest the PCM is what/where the problem lies.

The PCM has a couple specific reasons it'll turn off the A/C -- either an engine over heat, or at Wide Open Throttle.

An OBDII data reader might show the engine temp sensor is whacked out and the PCM thinks it's in over heat.

I'd suspect if the throttle position sensor had whacked out, you'd get a bunch of check engine fault codes.

One thing to check. With the engine off, key out of the ignition, do you have power to pin 30 on the relay? If not, a "semi permanent" jumper between pins 30 and 87a should bypass the PCM's control and get your A/C running.

Hmm you know what. I have a busted Temp Sender/Sensor on the thermostat housing.. the problem I'm having started right about the time it snapped off. Ill replace it this week and see if that tells the pcm to turn on my damn air!

And to answer your question YES there is power with the ignition off I have power to pin 30. I only need to drive the truck 10 miles a day. So I jumped it last week drove it to work.. did not take the jumper out and came out to a semi dead battery.

Thanks for your help. Ill replace that sensor and post back.
 






BINGO! Thanks for the suggestions.

I plugged the new temp sensor/sender in and CLICK the clutch kicked on!!

Thanks again.
 






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