Dear F150 Enthusiasts,

The clutch does not engage on my new 1999 Ford F150 XLT 4.2L V6. I have tried many of the steps on this forum without any luck.

No matter what I do, I cannot get any current on the plug that connects to the compressor.

I have replaced and tested the AC clutch relay and seems to be fine, I even exchange it for another one with no luck. Two of the terminals seem to be hot when the engine is on and the AC is selected on the cabin. I tried jumping the terminals without any luck getting a read at the compressor plug or getting the compressor to engage.

The cabin AC fuse (15A) seems fine too.

I have tried jumping the low-side cycling switch on the accumulator can using a paper clip, not getting the compressor to engage.

I have measured the static pressure on the system with the engine off and I get about 85 PSI on both the low pressure and the high pressure at about 90 Fahrenheit.

I tried adding refrigerant on the low pressure port but the refrigerant will not go in.

Any help will be greatly appreciated!

 

No point in trying to force more refrigerant into an already charged system. Besides, without the compressor engaged, it won't go in anyway.

Check the high pressure cutout switch for continuity and its connector for any evidence of damage.

Two of the relay's terminal should be HOT all the time - the high side of the coil and the power from fuse F5. When the system "demands" the AC operation to the PCM, it turns on the realy to rout fuse F5 power to the cluch.

The "demand" circuit consists of the mode switch (or EATC), the high pressure switch, and the low pressure switch which go into the PCM as the "demand" signal. This signal can be checked with a scan tool.

 

Thank you for your help projectSHO89!

The high pressure cutout switch (next to the high pressure valve) gives me a reading of 14 volts with engine on, AC ON, but only when the negative pole of my digital multimeter is connected to the negative of the battery. Connecting both negative and positive of the multimeter to the switch does not give a reading. The switch itself seems fine, but nowhere near new, do you have to empty (vacuum) the system to replace it?

The switch at the compressor is still not giving any positive reading.

On the positive note, I hit the compressor with a broom handle and It moved for about half a second, I could not make it move again no matter where I hit.

When you say, "The "demand" circuit consists of the mode switch (or EATC), the high pressure switch, and the low pressure switch which go into the PCM as the "demand" signal. This signal can be checked with a scan tool." Are you referring to a multimeter tool or a ODBII scanner?

 

That's how you're supposed to use a meter to make in-circuit voltage measurements. Unless instructed otherwise, the negative meter lead is always connected to ground.

What switch at the compressor????

OBDII scanner using Mode $06.

 

I am referring to the wires that plug to the compressor, ie, the compressor plug. I have not been able to get any reading from the cables in this plug.

I will check for continuity tomorrow (today is raining and I work on my truck under a tree), and will post the results.

I am a little embarrassed to recognize that this is going to be the first time I check for continuity. When I checked for voltage on the cutout switch yesterday the red plastic piece that is part of the plug came apart, I guess that could be consider "evidence of damage."

Thanks again projectSHO89!

 

I just check for connectivity on the high pressure cutout switch as well as the low pressure cutout switch and they both show connectivity (the multimeter beeps)

Any ideas?

 

If you hit it with a broom handle and it moved (engaged?) for a half second, might that indicate the gap is excessive? Should be .015 I believe?

 

It end up being a combination of a bad AC Clutch Relay and low R-134a levels. I had tested the AC Clutch Relay previously without luck, but seem like the "magic" touch with broom handle may had done the trick I exchange the AC Clutch Relay with the Trailer Tow Backup Lamp Relay and saw the compressor's clutch engaging intermittently for about 2 or 3 seconds. I added a can of R-134a and the compressor stayed engaged. COLD AIR IN THE CABIN!!!

I will check the pressure tomorrow with the gauges and will adjust for optimal performance.

Thanks mates!!!