Air conditioning compressor



2007 Ford F150 half-ton. No cooling of air at the outlet of the ductwork. Freon charge is good, I watched the tech pull the system down and hold it for the prescribed time period. Compressor will not start. I am being told that this means a failed compressor, but I am of the idea that the pressure switch for low pressure must have failed, or the orifice is stopped up. I am also being told that the compressor, evaporator, and orifice tube needs replaced in order to remedy this issue. The counter man at my local parts house cannot find in his computer any pressure switches, kinda making me think that everything is in the unit. In short, if I can avoid buying the compressor, I would like to. Any ideas? I appreciate your time on this one.


You apparently have no understanding of the AC system and the tech who “pulled down the system” either knows little or chooses to keep you in the dark. If someone connects a test light to ground and probes the compressor clutch connector with the AC on and the engine running the test light should be lit on one side and not on the other. If that is true you likely need a compressor and the other miscellaneous parts. If the light remains dark on both sides the circuit must be back tracked to find the problem. If the light is on at both sides the ground is lost.


I most probably neglected to explain step-by-step my efforts to figure this out sir.

I first suspected the refrgerant charge; that’s why I mentioned the freon recovery unit and what was done. The initial work was to check for a freon leak.

When that didn’t resolve the problem, I asked the tech to troubleshoot the air conditioning system. Continuity checks were in fact done on the compressor clutch. I did not witness that work, but the tech told me that there was power available for the clutch as well.

While I estimate that my knowledge of the air conditioning system in detail is finite, I believe that my basic understanding of how air conditioning works is sufficient to grasp the fault in the system, if you can relay it to me.

Thank you Rod.


There are in fact high and low pressure switches to be purchased seperately.
You tech should know how to test them.

What you do is essentially ‘fool’ them that it’s time to come on.
When the harness is unplugged from either switch you us a jumper in the plug to connect the circuit as though the switch is now ‘on’.


You could unplug the compressor clutch and jump a wire from it directly to the battery to see if the compressor engages and if the AC works.


If the clutch is receiving current and ground but does not engage it must be assumed that it would need repair or replacement. Most compressors today are not serviceable and require replacement.


The OP said that continuity tests were done, that only means that there is continuity through the clutch solenoid, it does not confirm that there is voltage or that the solenoid or clutch is any good. To test this, you need to use a jumper wire from the battery to the clutch while the engine is running and AC on to see if it starts to cool.

If it starts to cool, then you have to assume that the voltage is not getting to the clutch and troubleshoot why.

You can use the procedure in Red Knox’s first post, but I find it safer and easier to crimp a spade lug on a piece of wire and make a jumper to test the system.