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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1999 STS - engine cooling fans problem in Past Cadillac Vehicle Discussion; Relay one operates for slow speed, should ahve 2 fans wired in series when either any a/c mode is activated ...
  1. #16
    Mark C's Avatar
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    Re: 1999 STS - a/c cooling fan problem

    Relay one operates for slow speed, should ahve 2 fans wired in series when either any a/c mode is activated or coolant temp gets above 224, relays 1,2, and 3 are energized when EC Temperature exceeds 236. Relays 2 and 3 have to operate together, ther is only one path to ground for the coil thru the ECM. The only time relay one is deenergized is if the coolant temp is less than 224, no A/C mode selected, or vehicle speed is greater than 45 mph.

  2. #17
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - a/c cooling fan problem

    Still trying to figure out what's wrong. I took another look at your schematic. It appears that the compressor relay is somehow connected to all three cooling fan relays. This could explain why all three relays are clicking when the ac is turned on. Maybe the compressor relay is malfunctioning.

  3. #18
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    With checking the switched ground I mean that your test light is connected to battery + and you check on the 85 terminal, relay disconnected. But that's not your problem, since relays are clicking. Cleaning the relay contacts is good, but even better is to clean the opposite side, the plug contacts, and bend them back together, so the relay contacts get a good connection to the plug. But anyhow, if one fan kicks in your problem is situated in the wiring (or contacts) between the relays and the inoperative fan, and/or from the fan to ground. I don't think it's a/c relay related, since only the pcm is switching the fans, and it apparently does that in your case.

    Edit: all relays klicking means high stage, that comes from your refrigerant having a high pressure, since only one fan is working. That's normal operation, everything ok there. Move around your relays a bit while the fan is on, pretty sure eventually both fans come on, indicating a contact problem.

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

    "...But anyhow, if one fan kicks in your problem is situated in the wiring (or contacts) between the relays and the inoperative fan, and/or from the fan to ground. I don't think it's a/c relay related, since only the pcm is switching the fans, and it apparently does that in your case.

    Edit: all relays klicking means high stage, that comes from your refrigerant having a high pressure, since only one fan is working. That's normal operation, everything ok there. Move around your relays a bit while the fan is on, pretty sure eventually both fans come on, indicating a contact problem.[/QUOTE]



    I actually did take the casing off of each of the cooling relays and cleaned the contacts.

    I don't know if you read an earlier post here, but both fans DO go on when I unplug the ECT. Also, I still think that ONLY fan1 relay should click when I turn on the ac. But all three click...so I am wondering if it has anything to do with the compressor relay which IS connected to all three fans.

  5. #20
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    Relay one kicks in for low speed, all three for high speed. PCM is switching this by switching ground to relays (contact 85). A/C relay only gives signal to PCM so it knows that fans have to come on regarding pressures and temperatures in the system. I thought I read the other fan comes on when disconnecting ECT, my fault... Makes no sense though, maybe coincidence, maybe it has been tempered with. Still, if wiring is original only the part after the relays may be the culprit for one fan not working while the other does. And still, I mean cleaning the plugs, not relays, the part where the relay is connected to and the wiring is coming in/going out.

    Edit: the fan relays are not connected to the a/c relay, but they get the same positive switching wire, but they are switched by ground, so they have nothing to do with each other, except getting their "juice"off the same line.

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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
    Relay one kicks in for low speed, all three for high speed. PCM is switching this by switching ground to relays (contact 85). A/C relay only gives signal to PCM so it knows that fans have to come on regarding pressures and temperatures in the system. I thought I read the other fan comes on when disconnecting ECT, my fault... Makes no sense though, maybe coincidence, maybe it has been tempered with. Still, if wiring is original only the part after the relays may be the culprit for one fan not working while the other does. And still, I mean cleaning the plugs, not relays, the part where the relay is connected to and the wiring is coming in/going out.

    Edit: the fan relays are not connected to the a/c relay, but they get the same positive switching wire, but they are switched by ground, so they have nothing to do with each other, except getting their "juice"off the same line.

    To clarify: Both fans come on when I disconnect the ECT.

    I understand your first sentence. So, do I understand your next two sentences correctly that the PCM is "over-riding" the normal low-speed fan mode for ac? And this is because it senses an abnormal temperature and/or pressure in the ac system? And the fans will be on high speed? Is this correct? Isn't this the same circumstances as unplugging the ECT? If so, I would think that the RH fan should kick on!?!?

    Am I understanding you correctly?

  7. #22
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    You're right, it's not really an override, but normal operation, as is high speed because of high coolant temperature. Practically the same thing, hot refrigerant leads to high speed, as does hot coolant. Difference is that refrigerant gets hot quicker, therefore you figure high speed right away after switching on the A/C, because one fan isn't enough to cool stuff down efficiently. Even with both fans working and A/C on, high speed is common, like 20%, more or less... Disconnecting ECT triggers an emergency operation, since the PCM doesn't know the coolant temperature anymore (there's just one sensor on these engines, doing everything; gage, fans and PCM signal). At any moment one fan works the other is supposed to work also, there's just 2 grounds to be switched, always triggering both fans. So if one doesn't work, the failure has to be located behind the relays, circuitwise spoken. Except the wiring has been tempered with, which is quite common on a car prone to overheat for several reasons...
    In my case an aftermarket relay was built in, switching on one fan with ignition and disabling temperature dependent fan operation...

  8. #23
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    Re: 1999 STS - a/c cooling fan problem

    I do not intend to answer for el_dorado_mex but several of your statements/questions suggest (to me) that your understanding of designed engine cooling fan operation is less than accurate.

    Quote Originally Posted by palidin1029 View Post
    To clarify: Both fans come on when I disconnect the ECT.
    I'm not sure how significant that might turn out to be but let's set that slide for a while.
    ....So, do I understand your next two sentences correctly that the PCM is "over-riding" the normal low-speed fan mode for ac? And this is because it senses an abnormal temperature and/or pressure in the ac system?
    A/C Low Side Temperature and A/C Pressure sensors are used to control the compressor clutch. They have nothing to do with engine cooling fan operation.
    And the fans will be on high speed? Is this correct? Isn't this the same circumstances as unplugging the ECT? If so, I would think that the RH fan should kick on!?!?
    The fans do not run independently. If LOW speed is commanded, BOTH fans will be at LOW speed. If HIGH speed is commanded, both fans will be at HIGH speed.

    You say you can create a condition where both fans are running so that eliminates the likelihood of one failed fan motor. It would be worth double checking that one of the COOL FAN 1 and COOL FAN 2 fuses are not open. Both fuses are 30 A.

    As a definitive test of relay condition, you could borrow two SPST relays from another circuit (lighting?) and maybe borrow or purchase a new SPDT relay with five blades to try and narrow down the possibilities.

    Back to the ECT sensor. These sensors are very simple devices designed to present a specific value of resistance at a specific temperature. Failure can happen but is rare.

    The diagram is specific for your 1999 model. The only thing not shown is the ECT sensor input to the PCM.
    Attached Images

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    Re: 1999 STS - a/c cooling fan problem

    Thanks for the clarification...I suppose I will need to have someone familiar with this animal to physically inspect the wiring as I can't see any evidence of tampering.

    ----------

    JimD:

    The diagram is a bit different than what I have seen before (yours correctly show the two 4-pin and one 5-pin setup.) I need to look at it closer. Meanwhile, I did check the fuses for continuity as I did the relays. I will re-check everything...if OK, I will then start the process of substituting relays! Thanks for your input.

  10. #25
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    I wouldn't start to buy relays until I figured out what's wrong. Most likely it's no relay actually. Start checking voltage at the inoperative fan and go back from there until you get to the the point where voltage is present. Then ask yourself what is preventing voltage from going further. May be a relay not switching (for whatever reason), a loose contact or something alike...

  11. #26
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    Quote Originally Posted by el_dorado_mex View Post
    I wouldn't start to buy relays until I figured out what's wrong. Most likely it's no relay actually. Start checking voltage at the inoperative fan and go back from there until you get to the the point where voltage is present. Then ask yourself what is preventing voltage from going further. May be a relay not switching (for whatever reason), a loose contact or something alike...
    Remember, the RH fan DOES work when I unplug the ECT. Based on your previous comments, even though I start the engine "cold", you are saying that the system apparently wants to go in high speed mode when the ac is turned on based on the fact that all three relays are energized (they click). And you say it does this because of the coolant temp or the pressure. Because the RH fan is not kicking on in this scenario but IS kicking on when the ECT is unplugged, we apparently have two different sources that trigger the fans. And the trigger I need to investigate is the one related to the high speed ac mode. Is this correct?

  12. #27
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    Re: 1999 STS - engine cooling fans problem

    yes, all three relays clicking means high speed. and yes, because the fans are controlled by the pcm also a/c temperatures/pressures have their part in fan operation (once you'll get it working you'll figure that it cycles from low to high and back and even off, depending on your a/c status, even with "cold" coolant. one detail though, don't mix up the term "coolant" with the term "refrigerant", that's different things in different systems. it just happens to be the design of most (if not all) cars that the a/c condenser sits right in front of the radiator and uses the same fan(s), it could sit somewhere else and would need a different way of cooling and would have nothing to do with the coolant system...

    it's weird that disconnecting ect triggers both fans while normal operation only triggers one. the pcm has no way to decide whether one or both fans are working, it's both or nothing.

    i stick with my recommendation that you check voltage starting at the inoperative fan (you probably won't see any there, if you do your fan, fan ground and/or connector to the fan is the culprit). then go back to the relay (contact 87), measure again, and so on. use the diagram to find out what to check next. eventually you'll find a place where voltage is present, and that's the point where you have to find out what's going on. it'd be nice to post your results here to have more details on the failure and to be able to track down the problem.

  13. #28
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    Thanks for stickin with me here. Again, your explanation about the ac cycling and how that affects the fan speed helps me understand this a bit better. I will proceed with the voltage checking. In any case, I agree that it would be appropriate for me to post the final outcome so others can benefit from my experience.

  14. #29
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    Re: 1999 STS - engine cooling fans problem

    palidin29, Please go back and refer, once again, to the circuit diagram posted in #2. I removed the yellow wire #998 and the relay pins 87A, along with the note (along the wire line) that some pre-2000 fan relay setups would not have the 5-pin relays. It appears that the possibility of that extra black line and 2 relay pins not existing was a bit much for you to comprehend.

    ----------

    Quote Originally Posted by palidin1029 View Post
    JimD: The diagram is a bit different than what I have seen before (yours correctly show the two 4-pin and one 5-pin setup.) I need to look at it closer.
    See Post #2 again.

  15. #30
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    Re: 1999 STS - engine cooling fans problem

    I wasn't being critical...just being anal about the pin setup of the relays, actually showing the two 4-pin relays. No biggie.

    FYI: I just went out to the car and turned on the ac. The LH fan went on (my test light showed the black wire HOT and the other wire not hot.) The RH fan did not go on but my test light showed BOTH wires as being HOT. Not being an electrical guy, what does this tell us?

    WAIT...I forgot to tell you that when the ECT is unplugged, both fans run and they each have one HOT wire and one not hot.

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