A/C Problem - Compressor Clutch not engaging when warm

[duhtrev]

I'm having a problem with the AC compressor clutch not engaging when the truck is warmed up. When I first start it the truck, or if it is cold outside, the a/c works great, however once the truck warms up the a/c stops working. If I keep the RPM of the truck over 3000-3500 the a/c will start working again.

-I've checked the low side pressure to be around 35psi when the compressor is engaged and about 70oF out.
-Both the low and high side pressure sensors when unplugged caused the a/c to stop working (so I'm assuming they are okay).
-When the compressor is not engaging (when it should be) I get 0 voltage on its connector, I assume this to indicate the compressor itself is fine. I get 14V during the times it is working.

What else should I be checking or does anyone have any ideas? Thanks in advance for your help.

Vehicle :
1996 2.3l xlt supercab ranger
147k miles

 

[4x4junkie]

What is the high side pressure when the compressor is engaged?

 

[BRUTUS_T_HOG]

I'm having a problem with the AC compressor clutch not engaging when the truck is warmed up. When I first start it the truck, or if it is cold outside, the a/c works great, however once the truck warms up the a/c stops working. If I keep the RPM of the truck over 3000-3500 the a/c will start working again.

-I've checked the low side pressure to be around 35psi when the compressor is engaged and about 70oF out.
-Both the low and high side pressure sensors when unplugged caused the a/c to stop working (so I'm assuming they are okay).
-When the compressor is not engaging (when it should be) I get 0 voltage on its connector, I assume this to indicate the compressor itself is fine. I get 14V during the times it is working.

What else should I be checking or does anyone have any ideas? Thanks in advance for your help.

Vehicle :
1996 2.3l xlt supercab ranger
147k miles

sounds like you have a bad fan clutch. does it start working when you drive down the road? revving the engine to 3-4k makes the fan turn faster and pull more air through the condenser. if there is not enough airflow through the condenser the high side pressure will rise to the point that the high pressure switch will shut off the compressor.

test for power in and out of the high and low pressure switch when its NOT working

 

[kimcrwbr1]

check the high pressure switch when the A/C is on and not working. I agree with the fan clutch when the radiator gets hot it could be raising the system pressure to open the high pressure switch. Or the high pressure switch is closing too soon is there a adjusting screw on it between the terminals some do.

 

[duhtrev]

When you say "check the high side pressure switch" what am I checking? Voltage or resistance across the the sensor itself or across the wire harness/plug?
I need to get an adapter for my set of pressure gauges to check the high side pressure, as soon as I do, I'll report back. Thanks.

 

[4x4junkie]

When you say "check the high side pressure switch" what am I checking? Voltage or resistance across the the sensor itself or across the wire harness/plug?
I need to get an adapter for my set of pressure gauges to check the high side pressure, as soon as I do, I'll report back. Thanks.

Check to see whether there is voltage on one side of the switch, but not on the other (meaning it's been tripped).
If the switch has voltage on both sides (or on neither side), chances are good it's not the switch itself causing the problem.

 

[duhtrev]

I just tested the high and low side pressures when the A/C is operating properly and I get 40-45psi on the low side and 240-250psi on the high side.
My multimeter prongs were not providing reliable contact when stuck into the back of the high side sensor plug so I need to devise a better way to measure the voltage. As soon as I do I'll report back. Thanks.

 

[duhtrev]

Using paperclips I was able to measure the voltage of each pin on the plug while it was plugged in.
With the A/C on, when the compressor clutch was engaged and disengaged I got voltage on both pins of the high side sensor. So I'm guessing the high side pressure sensor is working.
I also tested the low side sensor in the same way and got the same result.

Any idea what else is in the chain of sensors that would prevent the compressor clutch from engaging?

Thanks.