A/C Control Circut

[440sixpack]

I'm trying to rebuild the A/C in my 1978 J10 and I'm at a loss. it was low on charge so I decided to restore it before recharging so I don't know if it worked before or not.

The TSM seems useless or I'm missing something. I have two wires going to the fuse block and one coming out of the unit to the fan motor. PERIOD.

I removed the entire system and found no pressure switch or cycle switch. most of the time there is a wire from the switch to the cycle switch and to the pressure switch then on to the compressor. nothing here. I cleaned the insulation off and found an expansion valve but nothing else.

what gives?

[Curly]

I'm working on a 77 Cherokee, same problem. What I found was this: The 2 wires from the fuse box are power in to the unit and power out to the clutch. There was no psi switch anywhere on the system. There was high pressure vent on the receiver/drier, that was how they dealt with high psi before the EPA got involved.

What I found was the power supply ( from fuse box) went to the fan switch. It had 3 wires. One wire in (power supply) one wire out to the blower fan and a jumper wire to the temp control switch. Temp switch then had a wire out to the fuse box, which was the clutch control/power wire. Clutch cycling was done based on position of temp switch. Fan speed was controlled by resistors built into the fan switch.

What I have done: Replaced the fan switch with a modern replacement, resistors still built in. New temp switch. Pretty much still wired the same except I had new hoses built and added a port for a Binary switch. The Binary switch will cut the compressor off if psi is too high or too low. I didn't like the idea of the blower fan power coming through the fuse box since FSJ's have a bad reputation for fire. So I used one of the relays under the hood to power the system and take the load off the fuse box. I did the same for the clutch, sending a wire directly to the binary switch instead of through the fuse box.
Wires are routed through the same passage the hoses go through.

Curly

[440sixpack]

Thanks, great information. I only have two wires out to the fuse block. then someone spliced the fan motor orange wire to the wire coming out of the RH side of the box. not sure what's going on there but that must have been the compressor wire?

In any even I like tour idea. did you put the cycle switch on the hose end as it enters the evaporator across from the expansion valve like a normal system? do you recall what fan switch you used that fit? oddly enough the parts house stocks a cycling switch for a '78 J10 that's why I figured it had one .


Sorry for all the questions but I understand A/C just enough to get in trouble.

[Curly]

I used this one from NAPA: TEM 901005, but an indak brand 35701 comes with a knob. Same switch. Check Amazon. For the psi switch, the shop that made my hoses told me he couldn't replicate the quick disconnect on the high side line going from the receiver/drier to the TXV. So I had him install a t-fitting in there with a 7/16-20 schreader fitting . So, I went from 2 hoses to 1 long one with the T. This is the psi switch I used. http://nostalgicac.com/oil-flush-switch ... reads.html The switch sits under the hood, above the tire where the sight glass used to sit. Right next to the compressor.

Curly

[440sixpack]

The binary switch can be screwed into the new drier I think. I know that's where my Challenger's is. so the fan switch is the cycle switch is the cycle switch. and you run a wire from it to the binary switch and onto the compressor. right?

I suppose you could put a regular cycle switch in but if what you did works that's easier.

[sonoraed]

http://oljeep.com/index.html stone simple go here for a wiring diagram

[Curly]

My new drier has a port for the switch, I just chose to put it under the hood, shorter wires that way.

[440sixpack]

I have that same diagram in my TSM but I cannot figure where the brown compressor wire ever hooks to a switch.

Did you use R134a or R12?

[Curly]

I have that same diagram in my TSM but I cannot figure where the brown compressor wire ever hooks to a switch.

Did you use R134a or R12?

There is no switch, except the temp control switch on the underdash control. Brown wire runs back to the fuse box. Inside, the brown wire became blue and hooked to my dash temperature control switch.
That is how it was set up on my 77 Cherokee. My system was 100% complete when I bought it, lacking only refrigerant. Compressor was there but blown. I took the entire system out, no switch anywhere on the hoses, evap or condenser. Only a blow off valve on the drier.

Curly

[440sixpack]

Okay now I'm getting it, it looked like the brown wire went to the fuse box but I couldn't figure out how that would work because it would be hot all the time, but if it's only using a fuse to fuse the wire from the control that makes sense. but my box has no blue wire so I need to find out why. someone must have pulled it out.

I'll start with a new fan switch and work from there.

[Curly]

Okay now I'm getting it, it looked like the brown wire went to the fuse box but I couldn't figure out how that would work because it would be hot all the time, but if it's only using a fuse to fuse the wire from the control that makes sense. but my box has no blue wire so I need to find out why. someone must have pulled it out.

I'll start with a new fan switch and work from there.

The brown wire isn't hot from the fuse box, it is just a pass through. The power for the clutch leaves the temp switch, runs to and enters the fuse box from the passenger compartment, passes through the fuse box into the engine compartment. The fuse box is just a place holder for the wire, not a power source.
The blue wire on mine may have been changed before I got it. 40+ years is a looooong time when dealing with wires and older cars.

Curly