Question about 1999 Cadillac Seville

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'99 Seville Climate Control stuck on 75 Degrees and HI Fan

I just acquired a 1999 Seville and the Climate Control will not remain at a different setting than 75 degrees and Hi Fan. If I change the settings, or even turn it off, the setting will return to 75 and Hi Fan within five seconds or so. I have tried resetting the custom settings without success, but the owner's manual is not too descriptive of how to do this. Only that it can be done.

Thank you for any help,


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The most probable cause is a failed HVAC control programmer. However, it may also be a failed cabin temperature sensor, causing the programmer to think it needs to set max heating. You can try removing the negative battery wire for at least three minutes and then reconnect it - this should reset modules in the car and may resolve the problem.

Posted on Jul 05, 2017


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Posted on Jan 02, 2017

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SOURCE: Need to know coolant temp operating range for 1988 Seville

Entirely possible and in range. Depends on outside temps and type of driving. The radiator is colled by electric cooling fans, controlled by temp sensors. Fans should come on automatically when a/c is turned on

Posted on Mar 27, 2009

  • 534 Answers


Ensure motor tune or other motor mechanical condition is not the cause of overheating, I assume the motor is actually running hot, - ensure the high gauge reading is not just a gauge sender problem. Check cooling fans are operating ok (as necessary when car warms up):- if not check
1) fuse,
2) relay operation,
3) heat sensor switch.

Check the coolant pressure cap is serviceable & of correct rating,
Ensure cooling system is correctly filled, bleed off any airlocks as necessary when re-filling,
Ensure radiator hose on suction side of waterpump is not collapsing at engine revs above idle (due softening),
If the motor has been severely overheated, the head gasket could be blown - look for combustion gas bubbles in the coolant resevoir.

If none of the above fix your problem, replace the thermostat again - it is not unheard of for a new thermostat to be faulty .

Posted on Sep 04, 2009

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SOURCE: 1999 cadillac deville 4.6 heater blowing cold

Besure that you have enough coolant. Your engine has head bolt issues and this allows compression gases into the sooling system, and this pushes coolant out and the heater goes cold before the engine everheats.... VERY expensive to fix correctly. There is a test to determine if exhaust gases are in the cooling system...

Posted on Nov 01, 2010

  • 37 Answers

SOURCE: display says it is running

Yes. Mine tends to run in the low two hundreds and will sometimes get to 225 before cooling down. I was told that this was they way they ran due to the aluminum engine. I have no idea whether it is true or not, but what I do know is that I have read countless forums from new owners asking about this, including myself at one point, and all the experienced owners tend to say,"Don't worry about it, this is how they run."
If you haven't already search 95 sls temperature. Try this one for starters:

Posted on Aug 07, 2011

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