Calling Electrical Guru's - A/C System

(1968 E-Type FHC) #1


I have the Retro-Air A/C system installed and have noticed that the ignition switch gets very warm (maybe even HOT) when the system is turned on for any length of time. Down here in Alabama, we want the A/C to stay on a lot!

I wired the system in accordance with this wiring diagram:

Is it correct to say that the power for the evaporator blower is coming through the ignition switch > fuse #6 and therefore the reason the ignition switch gets so hot? There are a lot of relays to figure out in there!

I am assuming that, even though all of my signal lights are L.E.D.s, it’s not advisable to simple move the white wire from the switched fuse #6 to the unswitched fuse #4, right?

Yes, probably best to install a relay but I’m having a little trouble figuring out where to install it. Any direction in that regard would be appreciated.

And all advice is always appreciated.


(Robin O'Connor) #2

Not an AC guru by any means but looking at the wiring diagram the one load off fuse 6 that I can see ‘might’ pull some current is the heater blower. Can you get a reading of the amps being drawn?

(Robert Wilkinson) #3

It looks to me like the entire AC circuit is powered, via relay contacts, directly from the battery. That includes “AC motor” which I assume is the blower motor used by Retro-Air? The only thing powered through the ignition is the relay coil. IMHO.

(Michael Frank) #4

Take a long, slow look at the diagram. It’s very clear. What you need to know is that the W lugs on a relay are the electromagnet winding. The C lugs are the contacts which carry the load. If you look carefully, you will find the load is connected to the B+ lug on the alternator. If you look at a factory installation, there will be a ring terminal with a 3/8” disconnect there for the purpose.

The W contacts take power from the inside of fuse six, they don’t go through the fuse. If there’s an extra lug, you can move that connection to the outside, which would be safer. But if you don’t wire the C contact correctly, you will burn out your ignition switch and risk a fire for sure.

(Dennismo) #5

There is a lot of current going through the switch.
The spades on the back that you clip onto are riveted to the switch and over time, the rivets loosen a bit. This creates more electrical resistance and resistance means heat is generated

I had the same problem. I took out the switch, cleaned the spade metal around the rivet until fresh copper colour, then cleaned the rivet and the landing the spade rivets to. Then I soldered the rivet/spade landing area.

Problem went away

If you post a photo of the rear of the ignition switch, I will highlight the areas that need to be cleaned before soldering

Dennis 69 OTS

(1968 E-Type FHC) #6

The good news is the car is up, bonnet off and battery out so I can step back and re-trace everything to make sure it is wired IAW the diagram. The bad news is I’ve run out of time and it will take me a few days to get to it.

Thanks for the recurrent training and suggestions. I’ll post back when I know more.


(1968 E-Type FHC) #7

A quick update.

I have only myself to blame. I have found that every time I “farmed” something out during the restoration*, mistakes were made that I had to “discover” and fix. I have some stories that might shock you.

In this case, I contracted with someone else (experienced?) to finish the install of the Retro Air system while the car was having the interior installed. The primary task was to finalize the installation of the evaporator unit and charge the system. I did not inspect every element of that task because the system worked. But now, looking closely at the a/c relay the ONLY wire connected to it is the NW from the alternator! Nothing else!

At this point I’m not sure exactly how the system gets it’s power but apparently it gets it through the ignition switch, therefore the heat. I will proceed to take 2 steps back, remove the evaporator and wire it correctly. It’ll take me a while but I will post an update when finished.

Dodged a bullet!


*Except engine, gearbox, rear dif, water pump, and carbs

(69 FHC ) #8

Indeed you did. …