1991 Nissan a/c problem

[RDNash]

1991 nissan truck with intermittent a/c electrical problem. blows cold when compressor engaged. freon normal level. I can go about 5 miles and then the compressor will kick out. Usually, if I stop at a light and turn the truck off a couple of seconds, the compressor will reengage. I replaced two relays under hoo on passenger side. I noticed the relay closest to the firewall gets really hot. Help?

[NISTECH]

you may have a pressure sensor problem. I cant see how an overheated reley would cause the system to shut down till the key is cycled, but if the relay gets so hot you cant touch it you should try to determine how many amps the comp clutch is drawing. Also if it has the A/C condensor fan get a look at its amprage draw. If it were so high it was shutting the system down it would blow the fuse to the system. So I doubt high draw is your problem. This is why I think you may be having a pressure sensor issue.

[RDNash]

The wiring diagram in the chilton book says there is a thermal protector between the a/c relay and the a/c clutch. Do you know where the thermal protector is located. If this helps, the a/c doesn't work very long when the sun has been beaming down on the truck all day. Alternatively, It works nonstop at night when the temperature is cool.Lastly, if it were the clutch, how many amps should it be drawing?

[NISTECH]

Its not an electrical issue with amprage draw other wise the problem would still exist at night. the pressure switch is located on the receiver/dryer or in the small a/c line located near the radiator. it has a small 2 or 3 wire connector going to it.

[RDNash]

Ok, I am very close now. I checked the dual pressure switch on the dryer for continuity and its ok. But I checked for an input voltage and I didn't get any. According to the wiring diagram, The thermal control amp supplies the voltage to the dual pressure switch. So, If i could just find the thermal control amp, I think I can fix it. Do you have any Idea where it is located? inside the cab or outside?

[NISTECH]

Its attached to the evap case inside the car behind your glove box.

[RDNash]

I found it. It was really hard to unplug. But I tested it when the a/c was working and it is fine. But when the a/c is not working, one of the wires is missing voltage. So, This leaves only the push button a/c switch and the picture shows a diode bewtween the switch and the thermal control amp(manual a/c not auto a/c). Please tell me this diode is part of the a/c button and my life will be saved.

[NISTECH]

That diode is possibly the light inside the a/c botton.