1999 STS - engine cooling fans problem
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1999 STS - engine cooling fans problem in Past Cadillac Vehicle Discussion; Recently purchased car. Had radiator flushed out, among other things. Problem: when the car is cold, if I put on ...
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    palidin1029 is offline Cadillac Owners Member
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    1999 STS - engine cooling fans problem

    Recently purchased car. Had radiator flushed out, among other things. Problem: when the car is cold, if I put on the a/c, the driver's side cooling fan goes on!! It should be the passenger side fan that goes on. How do I fix this? FYI: When I unplug the ECT, both fans go on. I could not find anything in the forum on this situation. Thanks....

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    Submariner409's Avatar
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    Re: 1999 STS - a/c cooling fan problem

    Both fans run together. With some A/C function set or if temp goes to 224 F then fans both run in SLOW; temp goes to 236 they shift to FAST.

    3 relays - Fan1, Fan2, Series/Parallel.

    Here's your wiring diagram.

    Read the cooling system, fan, and gauge sticky posts in the Northstar Performance forum. Maybe a previous owner jury-rigged the system.

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    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Thanks for replying to my post and attaching the diagram. The diagram appears to show three 5-pin cooling relays. My car only has one 5-pin cooling relays - and two 4-pin relays.

    I took your advice and read through the material. Unless my eyes are deceiving me, I could not find any information pertaining to my situation.

    I must clarify my original post...when I stated that the passenger side cooling fan should go on when the ac is turned on, I meant to say that it should go on as well as the driver's side fan. Currently, only the driver's side fan goes on.

    I was hoping that you would have run into this before - where only the driver's side fan goes on when ac is turned on...remember, the passenger side fan DOES go on when I unplug the ECT. And I checked all of the fuses and relays.

    Bear with me for a minute here...I thought I read that when the fans are run only for the ac, they are each only getting roughly 6 volts which allows for the low speed operation. You wrote something similar on March 30, 2012. I believe I also read that when the ECT is unplugged, both fans run on high speed. While I am not familiar enough with the fans to confirm the actual speed of the fan, it seems that the driver's side fan, when in ac mode, is running at HIGH speed. So could it be that, when the ac is turned on, the driver's side fan is utilizing "all of the voltage" and not passing any through to the passenger fan? If so, how can I fix this?

    Thanks....

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    Submariner409's Avatar
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    Re: 1999 STS - a/c cooling fan problem

    In SLOW speed the fans are relay-set to series operation - there is a voltage drop in that circuit, so fans loaf along. When some condition calls for HIGH speed operation the S-P relay opens and each fan receives full vehicle system voltage.

    If you will look at the wiring diagram again you'll see that the two fan relays - originally 5-pin units, may actually be 4-pin units - thus the note on wire #998 Yellow - "Deleted in some vehicles." (My take on "some vehicles" is at least the '98 - '99 MY cars)

    The 4-pin relays can be inserted either way (orientation) - look at the circuit diagram printed on the side of the relay - the solenoid and the power delivery circuits are connected to the diagonal relay blades - so no problems with placement there. The 5-pin (S-P) relay can be inserted one way only.

    One of the most often recommended checks is to simply remove each relay and maxi-fuse, clean the blades and install. That alone has cured half of the cooling fan problems in here.

    The "one fan using all the voltage" idea won't work - when the fans are set to series operation the voltage passes through the first fan, the S-P relay, to the second fan which is then the only ground circuit in that configuration: both fans must run IF the S-P relay is functional.

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    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Thanks again for replying. I will clean the relays and see if that resolves the problem.

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    el_dorado_mex's Avatar
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    Had the same problem, cleaning all the pins and "bending" them back together solved it in my case. Just a lot of exposure to the elements there and bad contacts after pulling the relays a couple of times... You'll need a small screwdriver for that. And patience...

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    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Thanks for your input. I have already cleaned the pins on the relays and the fuses. Still no success. Now that the pins have been cleaned, can I use something like a fingernail file to "clean" the sockets into which the relays plug?

    I have read that I could have some loose wiring and/or bad grounding at the fuse box. I see where the top part of the fuse box can be lifted up from the lower part. Do I need to disconnect the battery prior to doing this?

    I also read that I should make sure the PCM is OK. I am not getting any codes but still should check it. So I could not find any post identifying where the PCM for my car is located. Do you know?

    Thanks much.

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    Re: 1999 STS - a/c cooling fan problem

    Your PCM is inside the air filter box - for cooling flow. There should be quite a large wire bundle exiting the side of the box. The PCM is usually NOT the culprit in these fan witch hunts. The PCM is set and programmed for your car and your car only - a spare must be programmed by a GM dealer using your car's VIN and a GM Tech-II test tool set.

    You can lift the top half of the underhood fuse/relay box without disconnecting the battery - there are 3 or 4 large multi-pin harness connectors under there.

    Find another 5-pin S-P relay either at a parts store or a junkyard. Test substitute it or, if you have the clips, wire, and meter, test it for continuity yourself - both modes - voltage applied and voltage off - 12 VDC. The internal circuit is printed on the side of the relay case.

    Click the thumbnail to enlarge - use your < toolbar arrow to back out.

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    Re: 1999 STS - a/c cooling fan problem

    Since the drivers side fan runs in slow, then relay 1 is operating as it should, and since the passenger side fan starts when you pull the ECT, relay 3 is operating as it should. The only way I can see your drivers fan running, and the passenger side not running is if relay 2's contacts are stuck in the energized position (terminal 30 conected to terminal 87 all the time). This won't affect both fans runing when relays 1 and 3 are energized, but it does prevent power from passing thru the LH fan and into the RH fan so both fans run in slow speed. If this is the case when the LH fan is running, can you hear it? There is definately a difference in sound level between a fan running in slow speed, and two fans running is high speed.

    Pull out relay number 2 and put an ohm meter on the contacts. with no power there should be no continuity between 30 and 87, and a short between 30 and 87A, and with the coil energized there should be a short between 30 and 87, and an open between 30 and 87A. If nothing changes then your contacts are welded together.

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    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Mark:

    Very nice explanation. While I did test the relays and fuses, I did not test the 4-pin relays in a non-energized mode. I will do that now. Thanks you.

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    Quote Originally Posted by palidin1029 View Post
    Thanks for your input. I have already cleaned the pins on the relays and the fuses. Still no success. Now that the pins have been cleaned, can I use something like a fingernail file to "clean" the sockets into which the relays plug?

    I have read that I could have some loose wiring and/or bad grounding at the fuse box. I see where the top part of the fuse box can be lifted up from the lower part. Do I need to disconnect the battery prior to doing this?

    I also read that I should make sure the PCM is OK. I am not getting any codes but still should check it. So I could not find any post identifying where the PCM for my car is located. Do you know?

    Thanks much.
    You also can check if the pcm is doing what it should by checking ground continuity on both relays (pin 85 if I'm not wrong). Means that the pcm switches ground for both stages, 2 different wires. Let the car heat up with the relays unplugged and check with a test light. Should go on when temperature is reached. Be careful not to overheat the engine. But as already mentioned here, that shouldn't be your problem. To clean the plug contacts take them out one by one by lifting the little latch with a small screwdriver and pulling at the same time, gentle... In there bend them back a little (the part that actually makes contact), since that probably is the problem.

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    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Quote Originally Posted by el_dorado_mex View Post
    You also can check if the pcm is doing what it should by checking ground continuity on both relays (pin 85 if I'm not wrong). Means that the pcm switches ground for both stages, 2 different wires. Let the car heat up with the relays unplugged and check with a test light. Should go on when temperature is reached. Be careful not to overheat the engine. But as already mentioned here, that shouldn't be your problem. To clean the plug contacts take them out one by one by lifting the little latch with a small screwdriver and pulling at the same time, gentle... In there bend them back a little (the part that actually makes contact), since that probably is the problem.
    I did take apart the two 4-pin and the one 5-pin relays and cleaned the contacts. Still no luck. With engine cold, I had someone turn on the ac while I placed my fingers (one at a time) on each of the cooling relays. So I did this 3 times, one for each relay. Each time, after the several-second delay, I felt the relay that I was touching, click - and the driver's side fan went on. If I am reading the schematic correctly, only the fan1 relay should have clicked when I engaged the ac. Am I correct?

    About your suggestion on testing the PCM: Because my problem relates to the ac mode, can I confirm the clicks by using a light probe at each relay when I have someone put the ac on? If so, should I probe the 85 socket ? Thanks....

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    Submariner409's Avatar
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    Re: 1999 STS - a/c cooling fan problem

    The S-P (5 pin) relay should not click in - A/C calls for fans to SLOW = relay set to series operation.

    Are you quite sure no one has tried to make the fan system "better" ?

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    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Quote Originally Posted by Submariner409 View Post
    The S-P (5 pin) relay should not click in - A/C calls for fans to SLOW = relay set to series operation.

    Are you quite sure no one has tried to make the fan system "better" ?

    I appreciate your help and patience Submariner...

    If I look at the schematic that you showed earlier, if relay1 is energized, then 30 and 87 are connected and the LH fan goes on. Relay2 UN-ENERGIZED is in the 30 to 87A position, which allows flow to the RH fan. So I would think that relay2 should not "click" because that would divert flow to the ground, not to the RH fan.

    You wrote earlier: "In SLOW speed the fans are relay-set to series operation - there is a voltage drop in that circuit, so fans loaf along. When some condition calls for HIGH speed operation the S-P relay opens and each fan receives full vehicle system voltage." You are stating that the S-P relay (relay2) "opens" for HIGH speed. If it is "open", then 30 and 87 are connected, thus bypassing the RH fan since it is being energized by relay3. So I am confused.

    To my knowledge, the fan system was not tinkered with...at least I don't see any evidence of this.

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    Re: 1999 STS - a/c cooling fan problem

    Whatever. In SLOW speed the fans are wired in series. In HIGH speed the fans are wired in parallel. The S-P relay accomplishes this. (it would appear that the S-P relay and Fan2 relay are closed during FAST operation - full system voltage.) For SLOW, Fan1 relay closes, power travels through the Fan1 winding, through the S-P relay, to the power lead of Fan2 thence to ground - series operation.

    Fans always run together, not one at a time.

    I see the mistake - "the S-P relay closes to ground the LH fan".............. fixed.

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