Jetdriver69

I have been troubleshooting why the AC compressor on my 82 hasn't been getting any power when I discovered that someone in the cars past has removed the freeze switch and wired in a 5 amp in line blade fuse.

Why would anyone do this? Too cheap to buy the switch?

I have since received a new freeze switch from Roger and am assuming the temp probe goes into one of the small holes to the left of the expansion valve and right of the resistor pack connection in the evaporator housing. Please correct me if I am wrong.

Back to to the troubleshooting, I have good voltage from the AC control head to the hot lead that should have been connected to the freeze switch.

The control head was replaced by the PO with a Greg Brown rebuilt unit, so I am assuming it is still ok.

I have good continuity from the second freeze switch lead all the way down to the AC compressor, so no shorts that could be blamed for blowing the 5 amp blade fuse.

Up until a week ago the AC has operated normally with this 5 amp fuse set up, but now it will blow the fuse if the AC compressor is turning AND the FF Dynamics fan is running. It will not blow the fuse if either are running by themselves.

But the fan is wired so it comes on when the AC clutch kicks on or the coolant temp reaches 185F.

The electric fan is not powered through the 5 amp fuse, it just operates a series of relays that powers the fan. Power for the fan comes off the jump post.

After I install the freeze switch, is there any reason to keep the in line fuse and should I install a higher rated fuse?

Thanks!

Alan

The fuse is not a bad idea - I'd keep it after adding the freeze switch. However 5A is enough - do not add larger (do not - you will regret it). You need to figure out where the excess current draw is - something is not right with the fan relay set-up is my guess - use a DMM on 10A mode to see how much current goes to the fan relay connection (alone) if you directly connect power to it to activate the fans... split it out for this test. if you are driving only relay coils this will be no more than 0.5A - more likely <200mA/relay. More than this means you are driving something else...

Alan

Jetdriver69

Thanks, I will measure the amp draws today.

Could anyone tell me which hole the freeze switch temp probe goes in to? There are 2 in paralell, does it matter which one? (See above picture)

joejoe

One hole is for screw, the other for probe. Probe is long and should fit between fins on evaporator.

Jetdriver69

I had to make a mount for the freeze switch out of aluminum sheet as the PO or someone removed the whole assembly, but after painting in flat black it looks like it belongs there.

Now for the troubleshooting results to find the the high draw issue that keeps blowing the 5 amp blade fuse that was in place of the freeze switch.

I measured voltage from the AC control head to the freeze switch with battery only and it was only 10.25 volts. This is with a fully charged battery. Seems a little low?

Next I measured the same voltage with the car running - 12.90 volts at the freeze switch but the alternator is putting out 14.01 volts at the jump post.

Next I measured continuity from the power supply line from the freeze switch to the wire connector screw on the AC compressor and have good continuity from the freeze switch through the dryer switches and then to the compressor.

Next I put another 5 amp blade fuse in the holder and connected it to the freeze switch and then connected that line to a body ground. I wanted to see if the fuse would blow when NOT connected to the rest of the AC electrical system.

With only battery power applied, the fuse blew in about 2 seconds. So with my limited knowledge of electrics, I would say the AC control head is bad. Is that a relay issue inside the head or something else since I am getting DC power to the freeze switch, just a bit low.

The control head is rebuilt unit with bigger relay installed in Aug 2011, but I guess those can fail after a few years.

Just to be sure, I pulled the fuses to the electric fan and disconnected the AC compressor wire to preclude any chance that either of these components were the problem.

Within 2 seconds of selecting AUTO on the AC control head, the fuse blew. However, the fuse only blew when selecting AC. It held in ECO mode with the fan on full blast.

Any suggestions and can I replace the relay in the control head?

Thanks

SeanR

Why would you put a power line to ground? Of course that is going to blow the fuse, because that is what the fuse is there for.

There is nothing wrong with your head unit and has been told by both Alan and I, your issues are further down the line and most likely at the aftermarket fan. Do this, take the aftermarket fan wiring completely away from the A/C circuit. Unplug it. Do not plug it back in. Put the fuse in and run the car with the A/C working.

Do nothing else besides this. Then report back.

Alan

Your testing is bizarre... You asked, you got a specific answer - but it seems you decided to do everything but that...

Please do the test that was suggested - its the only one that makes much sense.

Your testing is stressing the relay in the head unit - are you intending to destroy it
?

Alan

69gaugeman

Can you take a picture of your multi meter? I think you may not have understood what Alan asked you to do.

Jetdriver69

Ok, I disconnected every possible path for electrics to the FF Dynamics fan. There are 3 relays, one 30 amp blade fuse, one 25 amp blade fuse and one 10 amp glass fuse. The relays and the glass fuse seem to be ok.

The AC compressor is connected and I installed a new 5 amp blade fuse.

This fuse is connected from the control head power source to the freeze switch and then the bottom freeze switch connection connects to the 14 pin connector then to the AC pressure switches and then to the compressor, right?

I started it up, selected AUTO and the fuse blew within 2 seconds again.

In ECO mode with the new 928sRus fan blowing full blast, the fuse holds without a problem.

If I disconnect the AC compressor and connect the fan back up, it still blows the fuse.

If I disconnect both the AC compressor and the fan, the fuse holds.

This whole set up has worked fine for 18 months and I didn't even know there was no freeze switch or that there was a 5 amp in line fuse in its place.

I have measured good continuity (0 resistance) from the freeze switch all the way to the AC compressor. That should rule out a short in the wiring south of the freeze switch, correct?

I have pulled the control head out but it doesn't appear to have been modified with a larger relay. No evidence of the control head ever being opened.

What should the voltage be coming out of the control head? Mine is only 10.40 volts.

Thanks for all the help.

SeanR

Leave the head unit out of your thought process ok? You've been looking at pictures of that huge bastard of a relay from radio shack and that's not what goes in a properly rebuilt head unit.

If you've disconnected the ac compressor and fans but are still blowing fuses, then you have a short to ground between the compressor and the freeze switch. If I were to guess, it's at or just after the 14 pin connector. Do you have an idle air control piece on the cross member? Are all those wires in great shape?

Jetdriver69

yes I do and will check.

Jetdriver69

I checked the idle air control and the wires looked ok. Checked continuity between the negative wire and the engine ground and are ok. But the idle control positive terminal was resting on a fuel line, so I moved that out of the way just in case.

14 pin connector looked ok, but the control line off the AC compressor that is tapped to control the electric fan looks very leak. There are exposed wires at the top of the splice which I will fix directly.

I will test again and report back. Might be a little while as I need to buy more male female terminals.

BTW, the 5 amp fuse does not blow if both AC compressor and fan are disconnected.

Thanks again!

SeanR

That positive is part of the A/C trigger and power circuit. If it was resting on the fuel rail then that is most likely where your short to ground is and what was causing the fuse to blow.

Jetdriver69

I hope it is that simple. I wrapped the fuel rail with a piece of shrink wrap type material and hopefully that will insulate it from happening again.

I am going to fix the frayed wire on the compressor splice just in case.

Will report back after lunch.

Thanks!

Jetdriver69

Sean
You are the man!

I found a loose ground on the left cam tower that hooks into the electric air valve. Tightened that up.

I put insulation material around the fuel line so it wouldn't short out the positive terminal on the air valve again.

I fixed the ratty connection down to the AC compressor.

Don't know which one was the problem, but now the compressor kicks on, the fan works and the fuse does not blow.

Thanks for your patience!