Here is the plug layout on the inside of the cab on the box (thermal switch)... helps if the glovebox is out to see it. Also, the blower motor plug terminates here.

The orange wire is the main feed from the Fuse box to the blower motor. It's a thick gauge 30A capable wire. The black with eye connector is the ground for the blower motor, goes to grounded side of blower motor plug in cab. And the black with yellow stripe goes to the blower motor plug inside the cab on the box.

Ambient temp switch on Rad Support... Honestly it isn't a necessity, the other end of the purple wire terminates here OR alternatively right to the clutch on the AC compressor if the ambient switch is bypassed.

Heres the other end of the purple wire inside of the engine bay at rad support... goes to ambient switch.


The vacuum diagram you found is correct also... matches EXACTLY what I have.

Trying to find some more pics of the last connector up top where the green wire terminates on a plug.... sifting through more pics.

 

Thanks man... it's a work in progress. Just like everything else I own... lol. House, truck, life... etc. Appreciate the compliment sir.

 

So the green wire with white stripe end up at the plug on the AC controls at the dash.... it's the one in the vac diagram you posted labeled "clutch". It is routed through the thermal switch I posted a pic of. The purple wire off that switch goes to the ambient switch, and then id routed directly to the clutch...

Only reason for the ambient switch is so ya don't turn on the AC in less than 55 degrees or so. Redundant feature really considering it already has that wire routed through the thermal switch on the evaporator in the HVAC box.
There's only one plug to the AC switch in the dash- consist of 5 wires... 12V+ off fuse box (red I think), one to blower (black and yellow stripe), one to AC clutch (green and white stripe). Other two on that plug I forget... but I believe theres another thermal switch in the ducting they go to.

Kind of hard to see, but best pic I have at the moment.


Plug is tough to see, but really self explanatory when ya get the AC/ Heat controls out... The vacuum plugs are also just plug and play too. Unless they were cut, hopefully they were not.


Hope this helped... If I had a couple hours to spare I could probably draw a diagram of the whole thing... it's late and I am tired though.

 

Flecker amazing, definitely a huge help! Found several thermal switches for sale online, so I got one on the way.
I'll have to make my own harness for that purple wire from the ambient sensor.
Strangely enough there's no purple wire coming from the engine bay into the deicing switch. I have:

• 2 black wires w/connector that connects to and orange and a black wire that goes into the condenser (Pictured on the 1st post)
• Single black wire from compressor to the deicing switch (bullet connector on the compressor side)

The second wire from the deicing switch is the green w/white wire but there's also a smaller wire coming out of it with a connector. Wonder what that goes to? I wonder if its possible my truck never came with an ambient temp sensor on the radiator support?

 

Hank - I noticed you're based in Burlingame; I am in the East Bay. There's an ol' timer in Livermore by the name of Dean, runs Dean's Auto Electrical and Parts (http://www.deansautoelectrical.com/) - he helped restore the wiring of my 75 back to stock from the rat nest all the previous owners have done.

If you end up getting stuck with your AC project, you ought to give him a call. I believe he plans to retire sometime in October/November and close shop, so not a whole lot of time - but he works magic on our trucks and it may be worth picking his brain or getting his services if needed.

Good luck!!

 

I have looked at this, then I've been thinking back to 1986 or '87. I bought my '77 in '86, it had just heater. I couldn't get cool air through the vent, did not realise that bug deflector was the culprit maybe, decided I wanted AC, so during a midnight shift, I spent a week of days on short sleep scrounging parts, etc. I stripped a JY '79 Super Crew of it's AC and a '73 in another yard, I used parts from both. I made a cardboard template of the hole in the firewall, and dash holes. My heater core is from the '73 as the '79 one leaked. I used '73 controls because I liked the script lettering. I do not recall ever having a temp sensor at the radiator support. The AC works but is low on it's charge, still R-12 in it but I may soon convert it. It shows bubbles in the sight glass. I have a couple pics I saved from somewhere, this one might help in IDing wires. Wish I could help more.


Not my picture, it is borrowed from someplace.
I spent hours and hours doing mine, had my whole dash out too. It's been used some but I really can't believe I did it. It's done, but I'd be just as happy today if I hadn't done it.

 

[Wrong Thread]

 

Morning, Redroad -

I realize this post is a decade old. Hijacking this thread as hankabilly's picture of the orange (30) amp points to the location where I have (12)v going in...and nothing coming out.

Both the heater motor and the A/C clutch responded to cabin control input prior to what follows.

Neither the blower motor or the A/C clutch are engaging from the cabin controls after I had the system charged with R134A yesterday morning. Current was applied from battery to the compressor clutch which engaged immediately and after ~(2) minutes the coils were cool....so, check.

Brought my 78' F350 CS/TS home and applied the multimeter beginning with the fuse block:

1. Remove fuse and check for (12)v at fuse block; check
2. Replace with new (35) amp, (12)v; check
3. Open dash and pull radio/control center; check
4. Side note...discard piece of crap Boss radio, but I check for (12)v on the positive coming off the lighter feed; check, (12)v
5. Inspect rear of control center nothing obvious
6. Pull fan control connector containing (4) wires from switch
7. Pull connector of orange (30)A wire coming from fuse box; (12)v, check, reconnect
8. Pull connector from back of mode control lever assembly; (12)v at orange female connector, check...attach (3) wire connector to control lever assembly.
9. With ignition off, check for power at orange wire connected to control lever assembly...nothing; check.
10. Turn key one-click to ACC and check for power at rear of connector starting with orange (30)A; (12)v check
11. With control lever assembly at A/C and then heater, check Green/White at rear of control lever assembly for (12)v...nothing
12. Same with Red/Black wire....nothing with lever positioned at heater or A/C

This is my first attempt at troubleshooting the mode control center. If my troubleshooting steps are flawed then let me know. It appears as though the lever control assembly electrical is not properly routing power from orange to either the A/C or heater.

I'd appreciate any guidance and my thanks in advance for your time.

Comnaver


A/C heater mode control lever assembly (Is rust on barb attaching vacuum lines significant? Doesn't appear to link to any of the incoming wires.)