So, I'm in the process of hooking everything up after a huge swap. I've abandoned my 84 shell for a 90 Formula shell after finding some significant cancer. One of the few things that didn't come from my original car is the HVAC stuff.

Originally, I couldn't tell any difference, but now that I'm wiring the engine bay, I've found a discrepancy. The wiring from my 84 has a different style connector. It has 4 blades. Three green in differing shades, and a black ground wire. One or two pop back out and run to the AC pump (which I also need to figure out - the 2-blade connector fits the newer compressor fine, but what I assume is the switch is completely different). On the 90, I also have 4 wires; black, green, red, and a light blue (I think - it's pretty faded).

Any chance I can just just replace\splice the newer connector with the old pigtail? Or am I stuck with swapping my old beat up HVAC stuff in (I really don't want to if I don't have to)?

Thanks,
Mike

 

Compressor Controls for TPI from 90 manual:


Compressor Controls for TBI from 90 manual:



Blower Controls from 90 manual:







Sorry, about the quality my lens is broken.

These are from an 85 which is probably similar to the 84:















Hopefully these will help.

 

Hi Allos,

Thanks for the diagrams! These will definitely help.

 

I don't suppose anyone that's good at this kind of stuff can help with the heavy lifting, eh? I suck at this stuff, haha.

 

Okay, I feel really stupid for not being able to figure this out, but can anyone help me walk through this? I don't want to burn something up via trial and error. Is it even possible to convert my '84 harness to the '90? Electrical schematics makes my brain fuzzy.

 

It sounds like your using the 84 engine harness in the 90 ?? If you have the 84 HVAC harness still ----> just swap the harnesses so the HVAC is a direct fit to your 84 ENGINE harness & your done. Using the 84 HVAC harness will eliminate the extra vacuum line on the controller. You can still use the 90 controller; it will plug right into the 84 HVAC harness and function normally.

 

I am using the 84 harness. I do have pigtails of the 90 for the blower motor and such, if I remember right. The colors are all different for the wires so it's got me all confounded.

 

There are lots of ways to wire it from basic to fancy. But first you need to understand your requirements.

* Do you have one or two radiator fans?
* Do you have an engine ECM that can control the AC clutch and radiator fans?

I'm guessing your new engine will rock and roll, so the AC clutch needs to be turned off when you go high revs. Your '84 may not have done that.

I had to cut and splice wires to create the outcome I wanted when I did my engine swap because the original wiring didn't do what I needed it to do.

 

I have a single electric radiator fan powered by a thermostat and controller. If I remember right it does have provisions for A/C on the relay. I don't have an ECM, though. The ECM, A/C, etc. was all long gone when I got the car and I didn't bother to piece it back together. I think technically speaking, my A/C compressor is from an 88 or some such. I got it along with the accessory brackets off of the boards here as I wanted to convert from v-belts to the serpentine setup. Not sure if that'll matter at all.

I'm not sure why my brain fights me on these things. I can fix or build just about anything I put my mind to, but I just can't wrap my head around wires that don't have the same colors, haha.

 

Is there some reason that you don't just swap the 90 HVAC harness out and replace it with the 84 HVAC harness.......... ?? this really is the simplest way to go if you're not a wiring guy. ( just install the correct Plug & Play harness and be done with it.)

 

So you're going to end up with something pretty basic, similar to the diagram posted below for the '85, but you'll want to tie in a method to trigger the radiator fan relay so that the fan is always running when AC is selected. The radiator fan will improve the performance of the AC system. I don't know if your relay is high side switching or low side switching. You'll need to figure that out and take it into account.

One last nice touch would be a throttle position switch that can interrupt (turn off) the compressor when you stab the throttle. AC compressors aren't made to go high revs. It may or may not be a big issue depending on the pulley ratio and rpm's potential of your engine. I'm not sure what is the rated speed of the compressor but it does have a rating.

Drawing things out on paper solves the color, memory, confusion problem. I draw things out all the time. I'm not an electrical engineer so I need to focus a bit to come to the right solution. And drawing it out makes me slow down and think about things, identify errors, and sometimes come up with a better idea. When I did my engine swap I drew out 7 different ways to control AC with pro's and con's before I made a decision.