my diagnostic skills when it comes to electrical are lacking... also for A/C...

I have the shop manuals, ive been over them a bit, but they dont seem to help much with the fans(replace the fans is the shop manuals recommendation).

I didnt drive the car for about 4 months...since February.

Probably havent used the A/C since last September. Worked fine then(well as good as C4 A/C can work.

Took the car the other day to get it inspected and when I got in to drive home, the car was HOT(like ~250 hot)... fans werent running at all. Car cooled down when I was moving so I know its not a radiator/water pump issue.

I checked the 5amp fuse on passenger side, its good. I checked the two maxi fuses(30amp and 40amp) and they are good. I replaced all 3 relays(I have no way to test the old relays, no 12v source of power, so I just replaced them all).

I can power both fans individually by pulling the relays(#2 and #3) and grounding the 12v input. So both fans function check ok.

I have no 12v in the 3rd relay(which would be the #1 relay). Not sure I should unless its commanded by the PCM for the A/C. Is there another fuse for this relay maybe I am missing?

As for the A/C, I have a feeling this is all related and the A/C didnt suddenly dump all its refrigerant(I dont have any gauges to check it).

When I turn the A/C on, the fans SHOULD both come on(as well as the compressor), but nothing happens. The blower fan runs, I can change modes, etc... but the compressor and radiator fans do not come on.

I dont "think" the 96 has fusible links as it has the maxi fuses.

The car is also showing a service engine soon light and im waiting to get my code scanner back from my buddy. Guessing its somehow related or possible a history code since I pulled the car into my garage without the 3 fan relays plugged in.


Anybody have a clue where to go from here? Like I said, the service manual, IMO, was not much help.

 

It could be low on Freon. I just went through this exact same issue. I doesn't just suddenly "dump" the Freon charge, just slowly leaks it off. 4 months ago it could have had enough to work, now doesn't.

 

I didnt run the A/C 4 months ago, it was likely last September(10 months ago).

That though, IMO, still doesnt explain why the main cooling fan wasnt running when the car got hot the other day...

I believe the fans not running when A/C commanded on is because the compressor on signal is also what turns on the fans.

 

Get a FSM and follow the troubleshooting. I has the automatic HVAC option and it was a big help figuring out what was wrong. Doesn't hurt to have AC tools like gauges.

 

ive got an FSM as pointed out in my first post.

Honestly it wasnt that great, but I havent dove into the A/C section yet.

Its first step in diagnostic of "electric cooling fans not running" is replace the fans...which isnt really helpful. I couldnt even find where it talked about the relays, but I know it has to be in there somewhere because I have seen printouts of it online.

I dont have any A/C gauges.

I have a few paths to go down from reading a few threads on here. I will be jumpering the low refrigerant sensor to see if I can get the compressor and thus fans to turn on.

 

Even if the car had no AC the cooling fans should have both run once the engine reached what 230°F? It's 219/228° for fan #1 and fan #2 respectively on my '94. So let's ignore the AC for the moment. The relay coils are supplied 12V and the PCM grounds the other side of the relay coil to turn on the relay and fan. Grounding the PCM line to each relay, with the key in "run" should trigger the relay and run the connected fan. If this works you have proven the fan, relay and all supply wiring. All that's left is the signal from the PCM and the wiring harness.

 

You can't tell what the temp is from the gauge. GM temp gauges lie. They (GM) even got caught making the temp gauge not register as much during the Duramax/LLY engine overheat fiasco.

Mine will get very hot by what the gauge says, and right before I recharged the A/C 2 weeks ago, I was having the exact same symptoms as the OP. My A/C worked fine last fall, didn't this spring. I will turn on the A/C to trigger the fans when creaping along or at a stop.

I am going to reprogram my fans to a lower turn on temp.

 

I keep seeing people refer to grounding a wire while everything is hooked up... I see zero way to do this with the relays plugged in as the connector is completely sealed on the back side and I have no desire to strip any insulation off of said wires.

With the relay un-plugged I can make the fans run by taking the 12v at the plug to the other pin that the relay would normally connect. So the fans are running and the plug is getting 12v. This is relay #2 and #3 respectively. I am ASSUMING relay #1 should have 12v some where on it, but it is the combiner relay for the A/C so if the A/C isnt coming on and thus triggering the fan relay I can understand why there is no 12v on the plug.


The 96 has two ECT's, one feeds the ECU and can be read via the electronic gauge cluster... The other feeds the analog gauge. The electronic one is a good value, ive never read on these cars where it was anything but...

I am thinking to snag a can or two of refrigerant and slap it in and see if it starts working, if yes, then I will take it to a local shop who has fixed a few guys C4 A/C issues.

 

The fans and their power feeds are good. That's excellent.

To ground the relay coil terminal that goes to the PCM take a fine wire, solid is better than stranded, (I like 23 awg from CAT5 cable) strip back about 1/2" and put it through the hole in the blade of that relay terminal. Fold the wire over towards the relay body and plug it back into the socket. Now you have access to the relay terminal without cutting or piercing any wires in the harness.

When I was troubleshooting my AC I got the refrigerant can with a pressure gauge. I jumpered the AC clutch and found that I had enough refrigerant. What I didn't have was a PCM that was accepting the signal from the climate control.

 

I was talking about the temp gauge in the gauge cluster on the dash (analog). GM is known to mess with how the temp is displayed there so as not to alarm people with the temperature showing too high. They did it with a reflash on the 2004.5 / 05 model year Duramax trucks while they were in their obfuscate/denial mode etc.

Reading the temps being reported via a scanner or digitally is more accurate of course. I will use the other temp display to see how accurate the analog one is in my car and also look at the temp via a scanner and see if all agree or disagree.

Regardless, with A/C you can tell right away if that is the issue doing a recharge.

Mine was leaking around one of the A/C ports. I saw oil on the line. That is what really tipped me off. The seals can go bad. I suspect I have a slow leak. Will get it repaired in a year or so.

 

I will try a can or two of refrigerant. But it wont be until at least mid-july as the wife and I are heading out of town for 3 weeks later this week and this car is a back burner car anyway...as is obvious from me only driving it like 4 times in the last year LOL.

 

OK, had a few minutes today.

Checked the codes: P1641 and P1642 which points to bad relays... Hmmm, relays are brand new. The old part number was superseded to a new part number and all 3 relays are all the same, according to the dealer... well new relays are 5 pin and relay 2 and 3 are 4 pin. I was "assured" this would not be an issue...

Put the old relays back in, cleared the codes, no more SES light. Got the car to 240, no fans at all.

My guess, now that I know bad relays can trip OBD codes, is that the original relays are ok and my issue lies somewhere else.

 

read here:

https://www.justanswer.com/chevy/2at...fans-will.html

it mentions a quick test you can do to see if it is the coolant temp sensor

 

The part # supercession mentioned to you is in error!


I believe I've seen a note in the past that the 4-pin requires a GM# 12177235 - A quick search indicates that's still correct. Having no idea what part #'s you've bought it's difficult to comment. I would think there's potentially other issues and you need to return to diagnostics. I don't see where you've ever mentioned the temps as displayed by the available 'digital' display. Was the 240 on the analog gauge or digital?

I'd think that even though the FSM relies on scanner for diagnostics there's enough information in the FSM @ 6-639 and forward to get you through.6-637 & 638 should cover AC fan request.

6-158 for wiring diagram. A '96 FSM is a bit different format than the earlier years. It takes a while to get acclimated!

Is your FSM a paper or .pdf?

 

I will try that, but that sensor is responsible for sending the coolant temp to the ECU. I can read the coolant temp on the digital dash, so my "guess" is that that sensor is functioning as intended. If it was not, I believe I would not get a readout on the dash.

I will re-check the part numbers, but I took the original relays in and the dealer told me the two 4 pins superceded to the same number as the 5 pin revision, said it just didnt use the 5th pin.

What is on there now is two 12077867 relays(in position 2 and 3) and a 12077864 which is in the position 1. The two that are the same are 4 pin and the different one is a 5 pin. The dealer told me the superseded part number for all 3 is 19118886 which are 5 pin relays.

----I just checked GM parts giant and they also say the 12077867 supersedes to 19118886. They also claim your part number(12177235) is also superseded by the 19118886 part number.

Regardless I dont think the relays are the issue as the ECU will throw a code if there is an issue with them. I believe my issue is not related to the fan relays.


The 240 is on the digital readout...there is no way for me to know it hit precisely 240 via the analog readout...

 

paper... I have both volumes.

 

Without a scanner, most of the diagnostics are hard or impossible to do.

I cant "command the fans on" via the PCM which a scanner can do.

 

Probably correct. I found it and just shared. However if it triggers the fans to work, well, you know they work and keep looking upstream in the circuitry.

 

I unplugged it. Car started hard(because the ecu didn't know what the temp was), ran rich, and the fans never came on. So I believed my problem lies elsewhere.

 

OK... here is a quick update.

I was able to borrow a Tech1 from a buddy, I dont have it for long so I will be trying to troubleshoot quickly.

I have run down the cooling fan checks and I can command the cooling fans on low speed individually and high speed combined.

I then start the car, command A/C on and I get no on signal being sent according to the tech1.

I dont have time tonight to mess with it further, but its leading me into the A/C system.