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2002 F250 Crew Cab Lariat
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Discussion Starter · #1 ·
The compressor will kick on and off above 2,000 RPMS. I hooked up a multimeter and can confirm when the compressor kicks off it is no longer getting voltage. The clutch gap is correct. Here are some pressure readings:

_____________________Low_High

Engine off (static).......78---75
Idle AC off...................78---75
Idle AC on..................34---30
Idle AC on..................48---48
2,000RPM..................40---40

When the clutch was engaging and disengaging it was around 30 for both.
Sometimes the fan would kick into over drive when pressures got around 30 and then the pressures would rise and the fan would slow back down.
The AC was blowing cold most of the time ( not when it was not engaging).
Around town I usually have cool AC, but when I get on the highway I have nothing. I am stumped. Anyone have an idea?
 

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Check the voltage at the low pressure switch. If the voltage is present on the input to the switch, but cycles on the output side, then the switch is opening when the pressure drops below its set point. As it is designed to do. CCOT. Cycling clutch orifice tube.

Your pressure numbers don’t make any sense to me. Low pressure side and high pressure side shouldn’t be the same with the ac on.


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Discussion Starter · #3 ·
I agree about the pressures. The only thing I could find says if they are equal, the compressor is bad. The compressor is relatively new and it works fine when it gets voltage.
 

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Discussion Starter · #4 ·
I unplugged the low pressure switch and it was getting 14V. When it was unplugged the compressor was not running. When I plugged it in the compressor kicked on.
 

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Again - the pressures are not making any sense. Here's my confusion. You say the a/c is cold when the compressor engages. That requires that the high side pressure is higher than the low side pressure. Equal pressures don't cool.

Just to eliminate any "operator error" - make sure of the following. Your adapters are locked on the a/c ports. Connected to the blue hose for low and red for high. All your knobs on the gauge set are tightened down. The knobs on both the adapters are turned to the right as far as they will go.

I have seen a few boo-boos in my career. Higher end multi-port gauge sets will allow you to equalize the pressures from low to high inside the manifold. I've seen people not get the adapters locked in, or forget to run the needle down into the Schrader valve. Any of those things would explain your readings. If your static pressure really is 75, you're likely very undercharged. As soon as the compressor engages, that would dip the low side pressure under the setpoint for the low pressure switch and it would cycle off. The pressure would rise, re-engage the compressor and start the cycle all over again.
 

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Discussion Starter · #6 ·
I just hooked the gauges up and got the same thing. They are hooked up correctly. When I shut the truck off the low pressure reading pins at over 350 psi and the high pressure was at 150psi.
 

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How is that even possible? The low side is twice the high and several times greater than any of your previous readings?


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Discussion Starter · #8 ·
I don't know. That's why I'm asking. I'm stumped.
159709
 

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Discussion Starter · #9 ·
While the ac is running.
Plant Motor vehicle Hood Gas Vehicle
 

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Discussion Starter · #10 ·
While the ac is running.
159712
 

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By any chance are the valves on the MANIFOLD on the gauge open? If so, close them as they should only be opened when evacuating or charging the system. They open and close opposite to the coupler valves.
 

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The only thing that seems to make sense is you have the manifold open AND the high side coupler shut off. Otherwise, the pressures would be the same running or not. Again - both dials on the manifold closed (turned right all the way) and both couplers engaged (it's not impossible to feel like it's on, but it hasn't caught), and both coupler knobs screwed all the way in AFTER you engage them. You start with the coupler knob turned all the way counterclockwise, make sure they latch on good, hook up your gauges, and then screw the coupler knob all the way clockwise to depress the Schrader valve.
 

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Discussion Starter · #13 ·
Tried a new set of gauges. What a difference. Low side was 40psi. High side was 380psi!!!
 

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Discussion Starter · #14 ·
It just registered 44psi low side and 440psi high side. When it gets that high on the high side, the compressor shuts off and the pressures drop and then the compressor kicks back on. That cycle repeats itself. The low side pressures seem ok. What would cause the high side to be so high? A blockage?
 

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It could be overcharged, have non condensibles, low airflow across the condenser, or a dirty condenser. A blockage would cause the low side pressure to drop as it would be starving the compressor.


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Discussion Starter · #16 ·
Condenser is clean. Today all the pressures were in close to in range. BUT something keeps telling the compressor to shut off--ie it keeps shutting the voltage off to the compressor when the high gets around 225psi. I think it is time to evacuate it, replace parts and recharge it. So frustrating getting results all over the place.
 

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It is hard to diagnose something when your readings won't stay still. It wouldn't hurt to replace the orifice tube. That will give you the opportunity to check the screen. You're about at that age where the "black death" gets common. Do you have the tools to draw a deep vacuum and recharge based on weight?
 

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Discussion Starter · #18 ·
Yes. I have everything to do the job. The truck actually has over 330,000 on it. Much less time to just start fresh. Looks like I can get a condensor, compressor, o-rings, orifice tube and accumulator for $210.00. Anything else I should do while I have it evacuated.
 

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Always replace the drier. Take the time to pull the evaporator core and clean it. It has 330,000 miles worth of debris in it now.


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Discussion Starter · #20 ·
OK. Thanks.
 
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