Hi Guys,

First time poster here. I am in the process of installing factory A/C to my truck that didn't come with factory A/C. It is a '95 F150 with the 4.9L and E4OD. I have installed all the components (i think) and the compressor will not turn on when i start the truck or when i turn the A/C switch on. If i run a wire from the battery to the compressor, the clutch will kick. This is actually how i charged the system.

So basically i have a fully charged system with no way to turn on the compressor. Is there something electrically that i'm missing? what electrical components are there on A/C trucks that are not on non-A/C trucks? I got the harness that goes through the evaporator/blower housing from a truck with A/C and the pressure switch on the accumulator is good i replaced that.

I saw in a wiring diagram something called an A/C clutch diode. What and where is this? does my truck already have this or do i need to get it off the truck with A/C? I appreciate any feedback. Thanks guys!

 

Welcome to FTE

Mounted on the backside of the heater/AC control panel is this mouthful:

A/C Vacuum Control Selector Valve Assy: F4TZ19B888B (Motorcraft YH565). Fits: 1994/96 F150 and others.

MSRP: $23.38 / FTEpartsguy.com price: $13.46

This is a multi-ported valve where all the vacuum lines connect...it also has the kicker switch on it that turns on the compressor, and those switches fail all the time.

 

thanks for the welcome and quick response. so if i go to the junkyard and get another control head it should work??? those switches fail a lot??? i really hope you're right!!

 

This is just one of the possibilities.

I listed the info, because after selling those valves for nearly 30 years (they've been used on most Ford cars/trucks since the mid 1960's), I knew that switch fails a lot.

At one time, you could just buy the kicker switch by itself from NAPA.

If it turns out to be bad, I wouldn't buy a used one...it may be no better than what you have now.

 

I'm going to go to the junkyard and get another control head and swap that out. if this doesn't work, what else could it be? besides that harness that goes into the evaporator box, are there any other electrical components that i could be missing?

 

I think what Bill is trying to say is: your switch is very likely bad, the one at the junk yard is also likely to be bad and thus a waste of time and money, so the smart money would be to spend $14 dollars on a new one. It's cheap.

The smarter idea would be to verify power into and out of the switch before anything else. There is also a low pressure cycling switch on the accumulator that is a common failure item. Check for power to that switch with the engine running and the AC turned on. There will not be any power to the compressor until there is 45psi of pressure in the system. The cycling switch closes at about 45psi.

 

thats good advice. you're right ill get the new part. when i googled that part number though, it came up with the fan speed control switch. but the A/C switch and the colored vacuum lines are one the other side of the control head, on the opposite side of the warm/cool dial. there is a plug with four wires going into it. i remember a purple wire. which wire should be getting power when i switch the A/C on? how much current should it be getting?

 

There Are switchs on the ac line that will cause you compressor not to kick on in case you have low pressure or in case your refrigerant is running to hot if I am not mistaken. check it out let us know !

 

lsrx101, i had the system fully charged by a professional but we had to run a wire to it from the battery. I also tried using a wire to jump that cycling switch on the accumulator to try to eliminate it as the failure. i also have verified power at that switch with engine on A/C on.

 

dre82s, the only one i know of like that is that cycling switch that lsrx101 was talking about. are there any other ones??

 

Do you mean that you have power to the cycling switch on the accumulator?
If so, the switch in the control head is ok.

The power flow is: B+.....panel switch.....cycling pressure switch.x...high pressure cutout switch.....wide open throttle relay...x.clutch coil......ground.

If there is power to the cycling switch, something is open between there and the clutch coil. (Between the two x's above) or a problem with the clutch coil or ground.

Is there power and ground at the clutch coil connector? If so, there is a problem with the clutch coil. If no ground, ground the black wire. If no power at the clutch connector, reconnect it and:

Move to the HPCO switch and check for power on the Dark Green/orange wire. If you have power there, jumper the connector. If the compressor runs, the switch is bad. If it doesn't runreconnect the switch and:

Check for power at the wide open throttle relay connector. There should be power on the Dark Green/Orange wire. If so, jumper the DG/O wire and the Black/Yellow wire. The compressor should engage.
If no power, there is an open between the HPCO and the WOT relay.

Email me and I can send you the wiring diagram of the AC system. Then all of that stuff I just wrote will make at least a little sense.

Since the system is charged and there is power to the LPCS, this should be an easy fix.

 

lsrx101, I can't seem to PM you but i have a wiring diagram and what you said makes sense. i'm going to test these connections tonight. keep in mind that my truck did not come from the factory with air so maybe i didnt get all the electrical parts i need. the only electrical parts i've swapped have been the control head and the wire harness that goes into the evaporator box.

 

What year was your donor truck?
The reason I'm asking is that much of the AC underhood wiring will have already been on your truck. 2 things come to mind:
-If the donor truck was r12 and your 95 was wired for r134a, you won't have an HPCO but the truck may have the connector. There's a break in the circuit. The HPCO is on the compressor manifold, if equipped. The connector is in the compressor harness near the back of the compressor..
- You could be missing the the WOT relay or the wiring is not in place for it.

I'll bet it's one of these 2 things since you have power to the LPCO and it's getting lost between there and the compressor.

 

lsrx101, i think you may have figured it out. the donor truck was a '94 (R12) and mine is a '95 (R134a) i didn't realize the electronics were different. What should i do?

 

94 was the first year for R134a on the F series trucks.

The high and low side fittings are coupler type fittings.

R12 fittings are screw on.