I have a 2000 F-150 4.3l and a/c compressor will not come on. I checked the pressure on both high and low side, low side is sitting at 90# and high side at 100#, with nothing engaging on clutch. I turn the fan to max a/c and fan to high and light comes on on dash for a/c, but I can't hear anything engaging on compressor and clutch looks like it is standing still while belt is rotating on engine. Had to check here to get fuse schematic and check fuses, but beyond that not sure what to do next. Any help greatly appreciated. Thanks!

 

Have you read the HVAC FAQs? If not, do so.

 

OK, just read all that will try jumpin out the switches...also found this link here to an older post, which may help me as well...will update when I figure it out (or ask for help if I get stumped again)

No power to compressor ? - F150online Forums

 

if both high and low pressures are the same, you most likely need a new compressor.

 

No, it means only that the compressor is not operating. No more or less.

 

Ok, so update is I checked and verified power is going to high press switch and to low press switch, but no power going to compressor. I read between 11 and 12 volts to both those switches, and like 200 millivolts to compressor so I assume that means really no volts. I tried jumping out both the low and high switches one at a time to see if switch is bad, but that produces no change. Also, I was wrong about saying the light on dash comes on for A/C when I turn switch on...it does not, now I can't remember if there even is a light that comes on when I turn the panel switch to a/c or max a/c or not. All the fuses and relays checked out. Pulled them and tested with ohm meter just to be sure, all seems ok. I am thinking maybe a bad switch on panel at this point, but not sure yet.

 

If it were a bad MODE switch, you would not have measured voltage at the pressure switches.

Can you tell if the clutch relay is energizing?

 

With a 2000 vehicle I myself would not spend much time troubleshooting things beyond running a fused circuit through the high side safety at least then to the compressor itself, this will cycle the compressor as required at stop lights or drive throughs etc. I myself wire the AC fan on the condenser full time with AC mode since it typically wil need it at stops and can only help! in fact I add another full time fan on my condensers .
You can have it by a switch inside or automaticlly by AC mode.
I use switches cause they are cool! I use the flip switches with backlights.

 

The pressures should be the same on both sides since the compressor is not on. The only thing it needs is enough pressure on the low side to allow the compressor to come on. You are not getting fire to the compressor itself. Somewhere inside the vehicle you are losing fire. Disconnect the compressor wire and run one directly from the battery and it should come on. If it does not the magnet is bad and probably what caused it to blow a relay or a fuse.

 

Let me start by saying, a lot of people don't have gauges and don't know how to use them. Before you go buy gauges and refrigerant, checking pressure, etc...run a hot wire straight to the compressor from the battery hot terminal. (unplug existing wire connection) If it doesn't kick in, no need to waist precious time on all that other stuff, you'll need another one. At least this way you'll know if the compressor is good in case you take it to a shop.
Finally, if you are going to try and take it off yourself, be sure to take the fan and the cover off 1st. Don't do like I done and try to cut corners for hours until I tore apart one of the refrigerant hoses. Not to mention all the cuts and soar hands as a result. I'm glad it was a junk yard vehicle instead of mine.
Good luck!

 

Not necessarily. If the magnet coil is bad it won't engage the clutch. That doesn't mean the compressor itself it bad. However if you do that while it's running it will either not engage, engage and squeal like a stuck hog because the compressor is locked up, run but rattle because it has internal problems or a combination of those.

 

I see. I would think the compressor has to come off either way. ls there anyway to test the magnet coil without taking the clutch apart from the compressor? And is it worth it, rather than to get another compressor?

 

The way to test the magnet is to hot wire it to the battery. If it pulls in then it's working.

 

Just wanted to thank everyone that responded...sometimes hard to diagnosed something over the internet, lol! Anyway, the issue wound up being way simpler than anyone thought, and I was on the right track at one point before I posted here. I had had a trouble code for temperature sensor but there was no coolant sensor on this truck...I thought at first the previous owner had modified the truck somehow and removed it. Since a/c had worked with no problems before I didn't think it would matter since the code had not been reset and had been present ever since I owned the truck.. Wound up being the cylinder head temperature sensor needed to be replaced. This started affecting my idle on the truck some time after posting this original thread, as the idle was going high and I virtually had to do a brake stand to keep the engine running when going from park to drive or reverse. Changed the cylinder head temperature sensor, and Whollah!!! not only did my idle problem get fixed but the a/c started working also!!!! Turns out that particular model only had a cylinder head temperature sensor...2000 F150 4.2l. Hope maybe this can help someone with a idle issue and/or a/c issue down the road. Thanks to everyone that replied as well!!!!

 

If the PCM detects an overtemp condition, it will disable the A/C compressor operation on the PCM-controlled clutches.

Would have been good to know about the fault codes earlier. Have to remember to ask....