BasketMan

New member here. I've read over a number of posts on troubleshooting A/C problems and need some help: Air conditioning worked great last summer, but now won't blow cold in my 2007 F150 5.4. I checked the compressor clutch and it does not engage when I turn the A/C on max. It spins freely both with engine off and with A/C on and engine running.

I assumed it was not engaging because the freon was low so I bought a can of refrigerant with a gauge. It was 95+ degrees outside and the engine was hot and running, I hooked the gauge to the low pressure side and the needle shot to 150psi which was the max on the gauge. I let the truck cool overnight and checked the next morning and got 100psi on the low side.

I wanted to test the compressor to make sure it still works so I disconnected the high pressure sensor (sensor just below the high pressure service port). Used my multi-meter and found 2 of the 3 terminals read 3-4v. With engine running and A/C on, I used a jumper wire to go from the hot to the dead terminal - nothing happened with the first one, but when I jumped the 2nd one the engine died immediately. I restarted the truck, jumped the sensor harness again and the truck died again.

-What is causing such high pressure in the low pressure side? Plugged orifice? Seized compressor? How can I test?
-What else can I do to troubleshoot?
-Why does the engine die when I bypass the HP sensor?

Thank you!