Climate control wiring

[Frogger2662]

I need wiring help.
Back story first. I have a 1984 F150 that has been rewired by a previous owner. Aftermarket harness and fuse panel. He did a decent job on what he did. Truck runs and drives fine with all lights and gauges working.
The climate control wiring was never rewired so I have no climate control. The truck came with A/C and heat. No compressor are condensor installed in the truck at the present time.
Is it possible for me just to wire the blower motor side and use just the heater and defroster? I have the pigtails voming from the back of the control panel. No other wiring.

[ArdWrknTrk]

With the truck "rewired" it's hard to know or understand what someone else has done (and now it's impossible to UNdo)

You need serious key on fused power to the blower motor, and hefty grounds. (I'd suggest a relay somewhere between the starter relay and blower motor)
If you don't have A/C you can ignore the compressor clutch and throttle kicker wiring.













What more do you need to know?

[Frogger2662]

The wiring harness used is a Ron Frances Express system. There is a 30 amp circut dedicated  for heat and air. I will be having more questons. This is the fuse panel being used.

[ArdWrknTrk]

I still wouldn't run 30A in, to the cab fuse box, and back out to the blower...

Somewhere Gary has all the drop tests and stuff when he picked up some relays from Texas Industrial Electric.
I suggested that he measure actual fan output, but I guess having real data is too much.  🤷‍♂️

[Frogger2662]

Ok. How does this sound. I can use the circuit in the fuse panel as my trigger for the relay I wold mount on the fender well. Bring in power to the relay from the battery. What gauge wire should I be using?

[ArdWrknTrk]

Does your wiring 'kit' still incorporate the Ford style fender mounted starter relay?

If so, I'd use the hot (battery) post* of the relay for a bus, and go with 10Ga primary wire to 30 of the relay and 87 to the blower.
Then I would make sure the ground side , from the resistor block to the controls was solid, and bring the ground side of the control to the back side of the firewall ground stud, going to the engine (just below the wiper motor)

Be sure to get a continuous duty rated relay.

[Frogger2662]

Yes it does have the starter relay on the fender. He updated the starter to the later style. What size wire should I use in the rest of the system after the blower motor.

[ArdWrknTrk]

A chain is only as strong as the weakest link.
If you don't want voltage drop and hot wires you should look at Gary's thread. 💡

[Frogger2662]

Thanks. Will do. When I have more questons I will ask again.

[ArdWrknTrk]

https://forum.garysgaragemahal.com/Next-issue-Heater-air-flow-tp145358.html

[Frogger2662]

The truck came with a/c and heat. It has controls for both still in the cab. Even have the original pigtails
cut off short. If I use just the heater for now can I wire it like the top diagram without any of the a/c wiring?

[ArdWrknTrk]

I posted both of them so you could see what you're up against.

I'm going to say, look at the AC model and notice "off" position , while all blower speeds are on the right.
If you have AC, you probably want to use the left switch to control the relay and the right to deal with speeds.

I believe the AC switch is piggybacked.
Be careful which row of contacts you make live.

I hate when people hack stuff before they understand how it works....

[Frogger2662]

I think I have most of it figured out. Going to use the a/c heater combo switch.
Two more questons. On the blower resistor there is 3 prongs grouped together and 1 seperate. The 3 together are high,medium and low. Which is which?

On the a/c-heater function switch can I leave out this leg of the circuit. It appears to me to be for the clutch which I do not have.20240229_212508.jpg

[ArdWrknTrk]

Correct.
Note that left and right are the same control, just that it is stacked, with two rows of contacts.....

So (for now) you only need to power the right hand one in the illustration.

If you look at the blower resistor you'll note a thermal fuse.
Be certain you have continuity through the resistor block before you pull your hair out.

AC  and heat only trucks (like mine) have different configurations
If you can't match the colours shown in the diagram, I'm going to suggest you just ohm out the pins to determine which of the three is what speed.

[Frogger2662]

Still fairly new to this level of electrical work. Can you tell me exactly what to look for when I perform the ohm check? I can follow instructions pretty well. Thanks

[ArdWrknTrk]

Look at the picture.
Orange/black is high and power in.
Lt Blue/orange is medium
Red/orange is low.


Blk is ground, as is the case throughout the truck's harness.

[ArdWrknTrk]

You need to check the ohms between the orange/black (common) terminal and the other 3 blades.