Backyardcarguy

Hello Everyone
Hope all are well

Well I am still working on my friends problem plagued 87 C4 with numerous electrical issues.
What I am wondering is it normal for the engine cooling fan to run when the key switch is turned on and the engine is cold??
I noticed the fan does increase speed when the temp gets upto 85 C or so but I have yet to see it not running.

As a second note: I also noticed that when the hood is up key off the under hood lights are fairly bright, as soon as I key on they dim down considerably. Also to note they do not get brighter when the engine is running. Alternator Voltage is about 13.68 volts at the alternator, battery is new, contacts/grounds that I have found (3 small) on trans bell housing and the 1 main ground part way up the bell housing toward the peak of the bell housing.

And finally I have found a factory ground strap located at the inner LH rear of the car, one end mounted to the main frame section the other wrapped aroung the LH side maker light harness. But I cant see where the actual mounting place should be for the loose end??

Thanks all for your time

Cliff Harris

The main cooling fan (behind the radiator) is normally controlled by the ECM. It is programmed to turn on at 228°F. Some people wire in a switch so that they can control the fan manually.

If you have the auxiliary fan option (fan in front of the radiator), it is controlled by a thermal switch in one of the heads (passenger side in '84 and '85, driver's side in '86 and later). The thermal switch turns on the auxiliary fan at 238°F. Some people put in a lower temperature thermal switch and some people wire the main fan to also operate off the thermal switch.

You need to trace out the wiring for the fan(s) and figure out if what you have is stock or modified. The main fan relay is mounted on the driver's side wheel well under the master cylinder. The auxiliary fan relay is mounted on the front of the radiator shroud on the driver's side.

Red86Z51

The main fan is also turned on by the switch in the high pressure A/C line. Mine went bad and the fan ran constantly with the key on.

Electrical bugs can be fixed, and most relatively easily, but you need to have THIS book to properly diagnose anything:

Backyardcarguy

Thanks Cliff!!

Well noted!!

Backyardcarguy

Hello White87

I have ordered the manuals just waiting on them to arrive.
Interesting that you mention the A/C High Pressure Switch! THe A/C compressor stays engaged all of the time as well, even when the system is in the off position. For now I just unplugged the A/C compressor cluth connection. Just one more of the many gremlins is this cars electrical.

VikingTrad3r

Hi Backyard,

I am subbing to your thread here because I have an 85 whose rear (main) fan is always on. I beleive the issue is the ac high pressure switch and i have ordered one for my 85. I would also add that my ac clutch was always working as well, and when i checked my pressures, the system was basically empty. Not sure where you live but where i live i can buy a replacement for r12. I put it into the car, repressurized, and now the ac blow CRAZY cold (that silver cannister gets frost on it?!!?). If I find the issue before you solve yours I will report my findings to your thread.

Regards,
VikingTrad3r

Backyardcarguy

Hello VikingTrad3r

Thanks kindly for your post!!
Just to give you and other readers a heads up on this problem.
I have actually disconnected all 3 pressure switches, 2 which I believe are for the A/C system, 1 low pressure safety switch and 1 high pressure switch. The 3rd switch or 2nd switch on the high pressure line I believe is for the engine cooling fan?? I have read some bits of information on various forums and I believe this switch is to trigger the main or rear engine cooling fan if you have the optional cooling fan installled in front of the rad. From what I have read this switch is supposed to turn on the fan as soon as the A/C is activated??? Thus I assume that this switch is wired in to the fan relay circuit so when pressure is in the high pressure side of the A/C system it completes the circuit to the fan relay?? Just guessing here!!

Anyways I have an additional problem with the A/C system, the A/C compressor clutch stays engaged even when the a/C system is turned off! So I thought mabe the clutch was seized!! but when I disconnect the clutch it disengages which rules out the seized clutch theory. I would assume the low pressure switch is installed into the system to prevent the compressor from being activated if the system is low or empty??? thus saving the compressor from damage??

Yup more gremlins in the wiring system!!
Thanks all for your input

VikingTrad3r

im in calgary

Backyardcarguy

Hello VikingTrad3r

Very small world!!

Born and raised in Calgary!!
Now working in Africa and living in Thailand.
Thus being in Thailand makes working on this 87 C4 even more challenging as you do not have any go to people here or very very few.
But we accept that here and expect things to take some time to resolve, receive parts from overseas etc.

Wish you well and enjoy "spring is just around the corner"

VikingTrad3r

Right on. Phom chaup ma Thailand! I actually speak thai enough to get by. My first businesses was from Thailand importing into north America. Raised in Calgary, works in Africa, lives in Thailand....let me guess...geologist, travelled to Thailand and fell in love, then took a job Africa making huge usd, and made home base in Thailand? that would be an amazing life!!!

Cliff Harris

Those switches are for the compressor. Low pressure switch won't allow the compressor to engage if the refrigerant pressure is too low. High pressure switch disengages the compressor if the refrigerant pressure is too high.

That switch connects to the ECM, which controls the cooling system fan.

Usually people have the opposite problem -- compressor won't engage. I believe in 1987 the compressor was still controlled by the blower control module (if you have the digital HVAC system). There might be a problem in the module.

VikingTrad3r

did you ever fix this issue with the main fan always on?

crowz

Actually one of the 3 switches turns the fan on when the a/c is on.

If it goes bad either the fan will run all the time or the fan wont come on when the a/c is on. Usually fails on the fan wont come on side.

This is outside the temp requirements and is to keep the fan pulling air across the condenser when sitting still to keep the a/c working at its best.

Edit : I didn't see where the post had info on it sending signal to the ecm. Sorry

antfarmer2

I have a place by Chia Nait how did you get your vette there and get the green book

antfarmer2

And if your in Thailand your ac is on all the time try turning it off