I picked up a '97 F250 w/ the 460 engine this past spring. I have been looking for a good one for years ever since I gave up my '96. I have been finding all kinds of electrical gremlins in this one, likely from previous owners *******izing the truck with poorly installed mods and removing them later. I think there was an alarm installed at one point and perhaps an aftermarket stereo. Someone installed a trailer lighting package all wrong which caused a short that kept the headlights from turning off without unplugging the relay or fuse. Right now the AC compressor does not engage when switched on. The fuses are good. I jumped it directly with the battery and it works, so it is somewhere between the switch and the compressor. I also have the "hey dummy there is something wrong with your engine" light on and the ABS light too. I know the easiest way to fix them is remove the bulb from the dash, but I have to take the truck through emmissions in my county every two years. I already changed the thermostat to get the engine to the proper operating temp for all the emission sensors and replaced the ABS sensor in the rear diff. I'll have to get a scan tool to find which sensor is going haywire. Does anyone have a complete wiring diagram for this model or know where I can find a good one? Haynes used to have decent ones, but not anymore.

 

There is a pressure sensor on the low side of the A/C system that keeps the clutch from coming in if the pressure is too low.

You can pick up a diagram from HELM INC or maybe one off ebay.

 

Thanks Bill. So I played with it a little more earlier today. I have voltage to the selector switch in the dash and continuity in the switch, so voltage in and voltage out. I don't know where the switch sends the voltage to. I assume it goes to a relay under the hood. I saw a switch behind the compressor, is this the one you are talking about? I could jump the contacts in this switch and see if I get voltage at the compressor.

 

A/C Cycling Switch

The A/C cycling switch is mounted on a Schrader valve fitting on the side of the suction accumulator/drier assembly. A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem as the A/C cycling switch is mounted and allows the suction pressure inside the suction accumulator/drier housing to activate the A/C cycling switch. The electrical contacts will open when the suction pressure drops to 163-175 kPa (23.5-25.5 psi). They will close, activating the A/C clutch (2884), when the suction pressure rises to 276-324 kPa (40-47 psi). Lower ambient temperatures (below approximately 1°C (30°F) during cold weather seasons will also prevent A/C compressor operation, because of the pressure/temperature relationship of the refrigerant in the system.

Note:
Temperature must drop to -4°C (25°F) to open pressure switch contacts. Contacts open at approximately -4°C (25°F) decreasing and close increasing 7.2-10°C (45-50°F).

The electrical contacts control the electrical circuit to the A/C clutch field coil. When the contacts are closed, the A/C clutch field coil is energized and the A/C clutch is engaged to drive the A/C compressor. When the contacts are open, the A/C clutch field coil is de-energized, the A/C clutch is disengaged and the A/C compressor does not operate. The A/C cycling switch, when functioning properly, will control the pressure at a point where the plate-fin surface temperature of the A/C evaporator core will be maintained slightly above freezing, which prevents icing and the blockage of airflow.

OR not likely your problem but could be this one also:

A/C Pressure Cut-Off Switch


Single

An A/C pressure cut-off switch (19D594) is used on all vehicles with air conditioning to interrupt A/C compressor operation in the event of high system discharge pressures, which could result in a loss of refrigerant.

The A/C pressure cut-off switch is a single-function refrigerant switch. It controls compressor clutch operation. This switch cycles as follows:

Clutch out at 2965-3241 kPa (430-470 psi) increasing pressure.

Clutch in at 1586-2000 kPa (230-290 psi) decreasing pressure.

The A/C pressure cut-off switch is located in the discharge line between the A/C compressor (19703) and the A/C condenser core (19712).



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Thanks for the help. I was able to jump the A/C cycle switch and figure out the root problem, low pressure. Got the system recharged and it works great now. For some reason I actually had to jump out the A/C cycle switch to get it to begin recharging. This diagram is exactly what I was looking for. I'll have to pick up that book you recommended too.

 

Is your 97 a California emissions truck? If it's not, you do not need a scan tool to pull the codes.