I've got double duty this weekend and need some guidance. My '94 F150's air died last summer. It had a very slow leak for about 3 years. I added a can of 134 a year and it cooled fine. Last summer it lost about 3 cans over a month. I added the leak detecting dye, but found no leaks. Pulled and held vacuum and recharged. Lost it in about an hour. Forgot and left jumper on low pressure switch and ran defog. Compressor locked up and smoked clutch. It's been disconnected ever since. Bought new compressor, orifice tube, oil charge and refrigerant today. Any advice on flushing system and finding leak. I thought it might be at compressor, but no dye came out anywhere visible. Don't want to tear into the evaporator/heater-core box just to look at it. Pressurize system & listen/soap test?
Second is nephew's 99 Escort base model. Not a truck, but diff vehicles of similar years should be close. Anyway, his AC quit suddenly. Checked and found still has some refrig in system, clutch not getting voltage. Checked both low and high pressure switches, good. Fuses good. Pressure switches getting voltage from dash switch. Got Hayne's manual for wiring diagrams. Shows pressure switches' signals going to PCM. There's also a white wire shown on diagram coming out of PCM that is apparently for clutch turn-on signal, but no diagram in between. I would think the PCM lead would control a relay to turn on compressor. Does it? where would I look if it does. BTW, two wires go to clutch connector. Neither is a ground, neither is white, and neither are getting 12v.

 

Go here: http://www.ackits.com/forum/categories.cfm?catid=20

There is a how-to on flushing and another on the Evacuate and Charging Procedure

 

While you are changing the o-tube, change the o-rings on the fittings....