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Thread: Temp Goes Up With AC

  1. #21
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    Quote Originally Posted by Ron View Post
    What's bugging me here is that the thermostat shouldn't let the temp drop below 195 F (180F if no converters), and, 220F is acceptable.
    Not to mention that the gauges are not known for accuracy.

    But I have to agree with Dave WRT the cooling system being able to handle anything the AC can throw at it, and then some.
    Yea, this has me thinking. My car runs cooler with the AC on. I think its be cause the fans run all the time. Makes me think my thermostat is no good. (Or missing) Of course this is not as serious as overheating, but probably hurts my mileage.

  2. #22
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Helirich View Post
    Yea, this has me thinking. My car runs cooler with the AC on. I think it’s be cause the fans run all the time. Makes me think my thermostat is no good. (Or missing) Of course this is not as serious as overheating, but probably hurts my mileage.
    There was an otterstat that turned at a lower temp that Hervey use to sell. I had one on my car and the fans kick on just a hair above the 1/4 mark. I now have the screw in otterstat and it kicks on at the same point. It is critical your temp sender for the gauge be the correct one to get proper readings on the gauge. I did testing on the temp senders somewhere posted on DMCtalk.
    Last edited by Bitsyncmaster; 05-04-2022 at 03:10 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #23
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    Quote Originally Posted by Bitsyncmaster View Post
    There was an otterstat that turned at a lower temp that Hervey use to sell. I had one on my car and the fans kick on just a hair above the 1/4 mark. I now have the screw in otterstat and it kicks on at the same point. It is critical your temp sender for the gauge be the correct one to get proper readings on the gauge. I did testing on the temp senders somewhere posted on DMCtalk.
    The "O" switch and the thermostat MUST operate at the proper temperatures in order to work together. You can't go just by the temp gauge, they can be inaccurate. Another point to make about overheating, if you have a bad head gasket and combustion gasses are leaking into the coolant the car can overheat especially when under increased load like when you run the A/C. It can't hurt to do a combustion gas test on the cooling system. When you have done all of the "ordinary stuff" and you still have a problem it is time to look for the less common causes.
    David Teitelbaum

  4. #24
    Administrator Ron's Avatar
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    I would shoot the cylinder head next to the gauge sending unit and compare it to the gauge's reading.

    Shooting the radiator's inlet and outlet can tell you a lot.
    IIRC, 1669 showed a 22F drop. (Most systems will show a 20-30F drop.)

  5. #25
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    Can Otterstat and AC Fan signals get in conflict?

    Same here! My car gets hot when I turn AC (about 220), and stays cool when AC is not running, what I checked is that when I use the car with no AC on, the otterstat works perfectly, turning fans on and off when it's needed, but when I turn the AC on, the fans starts right away, and here is were the fans starts to act strange, after some minutes with AC on and of course fans running, the fans turns off and the temperature starts to rise and then nor the otterstat nor the AC are able to send a signal to the fans to turn them on again,,, is like both signals get in conflict and they can't get the fans to turn on again, so I need to turn off the AC and after a few minutes the otterstat takes control of the fans again, any comments on my theory about this "signals conflict" I'm imagining is happening on my car?

  6. #26
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by rotproducciones View Post
    Same here! My car gets hot when I turn AC (about 220), and stays cool when AC is not running, what I checked is that when I use the car with no AC on, the otterstat works perfectly, turning fans on and off when it's needed, but when I turn the AC on, the fans starts right away, and here is were the fans starts to act strange, after some minutes with AC on and of course fans running, the fans turns off and the temperature starts to rise and then nor the otterstat nor the AC are able to send a signal to the fans to turn them on again,,, is like both signals get in conflict and they can't get the fans to turn on again, so I need to turn off the AC and after a few minutes the otterstat takes control of the fans again, any comments on my theory about this "signals conflict" I'm imagining is happening on my car?
    Each signal drives a 12 volt signal through a diode to the fan relay control signal. So as long as the diodes are good there should be no way any coupling of those signals at the fan relay.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #27
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    Quote Originally Posted by rotproducciones View Post
    Same here! My car gets hot when I turn AC (about 220), and stays cool when AC is not running, what I checked is that when I use the car with no AC on, the otterstat works perfectly, turning fans on and off when it's needed, but when I turn the AC on, the fans starts right away, and here is were the fans starts to act strange, after some minutes with AC on and of course fans running, the fans turns off and the temperature starts to rise and then nor the otterstat nor the AC are able to send a signal to the fans to turn them on again,,, is like both signals get in conflict and they can't get the fans to turn on again, so I need to turn off the AC and after a few minutes the otterstat takes control of the fans again, any comments on my theory about this "signals conflict" I'm imagining is happening on my car?
    Well, I'm wondering if your fans are drawing a lot of current (are they original)? When the AC is in operation, the fans are cycling with the compressor, and they spend a lot of time running. They may be pulling enough amperage to trip the thermal trip breaker when operating fairly continuously. Without the AC on the fans run a lot less (usually only when the car is not at speed) and the thermal trip gets a respite. Maybe the more continuous operation with AC is tripping the thermal breaker. This is when you notice the issue and you turn off the AC. Then the thermal resets coincidently with you turning things back on. Just a theory.

    Ron

  8. #28
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    If the fans are not cycling with the compressor, the circuit breaker is probably cycling them on and off. Upgrade the circuit breaker.
    David Teitelbaum

  9. #29
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    Quote Originally Posted by DMC-Ron View Post
    Well, I'm wondering if your fans are drawing a lot of current (are they original)? When the AC is in operation, the fans are cycling with the compressor, and they spend a lot of time running. They may be pulling enough amperage to trip the thermal trip breaker when operating fairly continuously. Without the AC on the fans run a lot less (usually only when the car is not at speed) and the thermal trip gets a respite. Maybe the more continuous operation with AC is tripping the thermal breaker. This is when you notice the issue and you turn off the AC. Then the thermal resets coincidently with you turning things back on. Just a theory.

    Ron
    I don’t believe my fans cycle with the compressor. They just turn on with the AC switch. The compressor can cycle (or not), but the fans are on as long as the switch is on.

    Edit, thinking more, maybe they just appear that way to me because they are on with the key when the car is not running. My compressor doesn’t cycle much.
    Last edited by Helirich; 05-11-2022 at 10:06 AM.

  10. #30
    Administrator Ron's Avatar
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    Quote Originally Posted by Helirich View Post
    Edit, thinking more, maybe they just appear that way to me because they are on with the key when the car is not running.
    Yep.
    (As David reminded me...Power from the AC switch goes through the cycle switch first....)

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