Hiya Allen!
I'm a newbie to the forum too! I've looked in for a few months but after reading your too familiar to be true postpost I took the plunge.
I too have an '85 with very similar problems. She's my first Vette and I'll never be without one again in life! Poor gurl has been rode hard and put up wet but she's mine now and I'll take good care of her. So much for the preamble...My 85 has the aux fan in front of the condensor. As far as I can tell this a factory item at least judging from the wiring. Like yours, my aux fan never turned on by itself. I checked the fan motor with batt voltage and found it to be good. Unfortunately my baby still gets too warm, routinely 215-220 in traffic and at lights. I tracked the switches and senders...temp guage sending unit is a single wire sender on the drivers side cyl head. Turn the key on, disconnect the sender and apply grnd, guage reads 299. I replaced it anyway. Aux fan switch is a single wire connection in the same boss in the pass side cyl head; turn on the key, disconnect the switch, apply grnd, fan turns like a hurricane. This switch is factory set at a whopping(wtf were they thinking) 230 degrees. Replaced it anyway too. Put the scanner on the car and found that the switch closed as advertised at exactly 230 degrees. Shuts down at 215. I have a clue about the MAT sensor in the plenum. Thinking that one turns on the main fan but I'm not sure. Just waiting for ups to deliver the cooler aux fan switch unit I ordered from MADVET. And looking hard at the MAT relocation kit from them too but not sure if that will really help me and my particular application. My car was missing the center portion of the air dam when I got her and I found that after replacing that piece driving temps dropped dramatically. From my own experience...take good care of your air dam! Park away from the curb and walk a couple extra steps!

So here's my question...sometime in the past she was converted to r134. Seems to cool fine except when I throw the fan switch to "high". Blows the fuse everytime. Checked the blower motor and all is well there. I have low, med 1 and med 2, but no highspeed without catastrophic fuse faliure! Help?

 

So it sounds like some former owner of my car replaced that sensor with a much lower one. I wasn't sure of what safety temp it was supposed to come on - but was very sure above the 195.

As for your problem... I just poured over the diagrams...

Does the fuse blow in High ONLY when a.c. is on? Or does it also blow when say heat or defrost is on?

According to my documentation... The fan switch has 4 wires:
hi is orange 52
m2 is lt bl 72
m1 is tan 63
common is yellow 51.

The low (m1) and med speed (m2) go to something called a resistor assy.

AND the high speed go to something called a/c hi blower relay. Where is it, I don't know. Yet. But here is the wiring diagram. Mind you I am trying to decifer it as I go along. The coil is energized off 150 black (which is connected to blower motor, pressure cycling switch,washer pump and other things - its common ground). The other side of coil is 52 orange wire. Remember that orange wire being the high speed at switch on dash? Output of the relay is 65 a blk/red wire. Circuit 2 is red which goes directly to engine harness for high speed. And the low and medium fan is 101 a dk blue.

I would start at the a/c hi blower switch... You can check the input sides of the coil for shorts. You could replace it. Or else try it with the dark blue disconnected (this would get the low and medium off in case the contacts of relay are fused / melted together).

I find it very difficult to think and write in these little text boxes!

Oh now I found some other diagram. They say to replace the blower switch or blower relay. My background it electronics to the component level. The relay is RH frontof dash, on blower motor.

Hope this helps narrow it down. Please let us know!

Allen

 

Allen,
Thanks for your reply! I tried the blower motor relay first rattle outta the bucket and it had no effect; still blew the fuse. I'm taking the good info you provided and will pull the dash apart tomorrow to get a look at the controls and the fan switch. The two lower blower speeds work as advertised...it's when I turn the switch to high that the fuse pops. It doesn't seem to matter whether the a/c is on or not...selecting the high speed fan pops the fuse. That was why I replaced the relay first hoping for a simple fix. I'm not looking forward to what I might find back there...hoping now it's just a switch replacement...will advise. :cool:

 

Allen,
I took the dash apart last night and I couldn't believe the mess back there. LSS I did a lot of house cleaning in the wiring dept! It was all cobbed together back there. I couldn't find any obvious failures...burned/overheated wires, chaffed or crimped or broken wires either. So a lil frustrated I just cleaned everything as best I could and put it back together. Guess what? It works! I can turn the fan switch to high and it doesn't pop the fuse! Too cool! Do you believe in karma? Was it her way of saying, "I need TLC and I need it now?"

Thanks for your good info, it helped! :hurray:

 

Update...I've been dogged by a vacuum leak. Couldn't find it. For no particular reason I was inspired to pull out the vacuum resevoir(?)ball gizmo in the front left fender. I took it out, rolled it around in my hands and on the bottom out of view when installed was a hole the size of a BB. Quick temporary electrical tape patch and things started working really well and the hitch in the idle smoothed right out. Gettin better every day! :cool:

 

Does anyone think that the 2 different temp sensors are the same type? I mean will they thread into either position on the block? What I am wondering is - could some prevous owner have bought an after market sensor thinking this would lower the main fan temp & place it in the aux fan position? Looks like I am really going to get into the wiring of this puppy.

Another confusing thing is the manual has a Vette 1A and a Vette 1 C. Does anyone have any ideaas to what the difference is?

TIA.

Allen

 

Allen,
The temp sensor and switch are not the same and have different connectors on them. They are similar in size, weight, and appearance except for their connectors which are not interchangeable. The temp sender has a male blade connector and the wiring loom has a female connector with a plastic clip. The switch has a larger round female connetor and the male connector on the wiring loom is also larger. To replace a sender with a switch or vise versa would require cutting and splicing the wiring with new connectors. Of course you would spot that right away.

When I was replacing these items I asked the guy at AutoZone to look up all of the temp senders and switches for the car and pull them. I then compared each one while at the counter. There were three. The guage sender had a single male connection, the aux fan switch had a single female connector (it's just a ground BTW), and the the third (mat?) had a two wire connection of the male variety. I'm still waiting for my cooler switch for the aux fan to arrive. For giggles I spliced a rocker switch into the fan wire for manual operation. Works great! Good luck! :cool: