OT: '90 F250 2WD 6 cyl AC problem

[Slowpoke]

No AC, clutch does not pull in, no power at clutch terminal. 30 Amp breaker reads closed with ohmmeter, has 12v on both terminals with key on. With engine running at idle, turn on AC and idle speed drops, but AC clutch does not engage. Blower motor comes on when AC/heat is selected. Heat does not seem to work either. I can"t find a schematic for the "90, so I have to ask the expert(s). Is there a switch behind the AC/heat panel on the dash?
Thanks

 

[Anonymous-0]

It's a Ford. To many extra wires and relays for no need.

 

[robgIN]

Did you try jumpering the clutch cycling switch? should be in the low pressure hose or on the reciever/drier.Check for power at the compressor connector too. If you got power at compressor the field coil may be bad.If jumpering the switch makes it kick in you have a bad switch or low on freon.

 

[Bob M]

Could be the A/C system needs recharging (there's a pressure switch that opens and disables the compressor if the refrigerant pressure drops too low).

Pull the electrical connector from the A/C clutch. Ground one clutch terminal (doesn't matter which one) and use a jumper to supply 12 volts to the other terminal. If the clutch now engages, most likely the refrigerant pressure is too low and the system needs to be "gassed up".

 

[Another B Puller]

Had a 98 Ranger that every time you hit a bumb the clutch would disengage. If that is your problem there are shims that you can take out to take the play out. Worked for me still have factory comp. at 345000.

 

[Slowpoke]

You're right on!
Way too many wires and connectors.

 

[trucker 40]

With a test light,check you wire that goes to the compressor see if you can find out if its broke somewhere.Look the wire over good and see if has been probed by a test light before and inside the wire is green,probably broke right there,or you might not even be able to see where its broke.Also,dont have a schematic of it but there is probably some switch somewhere that is unhooked or the terminal has been hot,like your fan switch.The terminal that runs the fan may be fine,but the one that kicks power in for the compressor is probably burned up,and if thats the case,you will need to replace the wire end too probably.Also Ive noticed that when that happens you most likely need a new clutch too.You might see if it is dragging like the bearing is out and maybe get lucky and replace just the bearing,but if its been real hot it is probably about shot.
I havent worked on a lot of Ford air conditioners,but Ive worked on a lot of truck air conditioners,and most of the time when they wont kick in,and you have power,its the switch in the cab.Either the wire end or the switch or the wire going to the clutch.Ford could be completely different.I would about bet that its not though.

 

[Brian Jasper co. Ia]

There is a switch in the the mode selector. It provides battery voltage to the compressor clutch through the cycle switch on the accumulator. A jumper wire in the cycle switch should make the compressor run constant. You can test the clutch by applying battery voltage and a ground to the clutch terminals.
When you select either A/C or defrost, the compressor is supposed to cycle and the idle speed should pick up a little to compensate for the extra load at idle. If you see that little jump in idle speed that indicates that the PCM is seeing the 12v signal from a closed cycle switch. Either have a broken wire or faulty clutch coil on the compressor.
The black with yellow tracer goes between the cycle switch and clutch. There is also a clamping diode and resistor in that wire. If you find you have an open in that wire, it's very important you don't eliminate that diode when fixing it. The diode disapates the voltage spike that is generated when the magnetic field collapses. That spike can wipe out the PCM.