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i have a 96 sts and the heater only blows out hot on 1 side of the car the drivers side, the passenger side blows out cold. this happens when i use the defroster also. what would cause this? and how do i fix it?
 

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CAD4DAD said:
i have a 96 sts and the heater only blows out hot on 1 side of the car the drivers side, the passenger side blows out cold. this happens when i use the defroster also. what would cause this? and how do i fix it?
Let us know if the flush fixes your problem. I have same thing going on with 94 STS, but just the opposite side. My drivers side footwell area has no heat, but passenger side does. I am not able to flush due to a ThermaGasket additive in my coolant that needs to stay there for another 200 miles. So watching for your results.
 

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If you are getting heat on one side, it is not likely the heater core, since the heater core is not separated into sides. It is more likely something in the HVAC controls.
 

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1991 Eldorado (Gone) ; 2001 Seville SLS (RIP) ; 2005 DeVille
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JPL189 said:
If you are getting heat on one side, it is not likely the heater core, since the heater core is not separated into sides. It is more likely something in the HVAC controls.

I could be wrong, but I swear I've read several threads on a half clogged heater core causing this exact issue. Recall reading up that Drain-O may be worth a shot.
 

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White Diamond '03 DHS (with DTS floor shift)
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Yeah, the heater core gets clogged on the lower half and the air is stratafied through the duct as I recall the explanation. Flushing is worth a shot.
 

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Trench said:
I could be wrong, but I swear I've read several threads on a half clogged heater core causing this exact issue. Recall reading up that Drain-O may be worth a shot.
I read through a ton of messages on here about this same thing. They are indicating the flushing is successfull on 93 and later models. Those years did not have a seperate vent ducting at the bottom. From 94 they put in the lower air controls at footwell.

Correct me if I am wrong.
 

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I had the exact same problem with my 96.. i just keept playing with the hvac controlls, adjusting temps and such and it finally unstuck itself.. aparently one of the blend door acuators was stuck
 

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White Diamond '03 DHS (with DTS floor shift)
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If it is a sticky actuator, that will sometimes work. My '97 Deville did that in A/C mode (dual zone temp). Running the temp up to 90, then back down, always cured it.
 

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I have not flushed the heater core yet, but I did run temps up and down, as Ranger explained. What I find is a brief period of heat, cool, warm is there as the mode is being changed over. So most likely heat is being directed wrong place. I have another 100 miles to go before flushing out this ThermaGasket, and then do heater core same time.
 

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actuator door. I had the same thing. If it's under the driver side then its more expensive to fix. I had a problem with the one under the passenger side, about $171 to fix as i recall.

Gus
 

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I just flushed the ThermaGasket out of my cooling system, and was about to flush heater core. Only is near impossible to get to those heater core hoses lossened. So I left heater running max temp 90 degrees, and flushed 4 times the entire system with hose water, then last time with bottled distilled water. Interesting because now the drivers side is blowing hot air. Before the flush only inside temp air was blowing out drivers side.
 

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Ranger said:
Sounds like Thermagasket clogged the heater core.
.

Wife claims its been that way ever since we got the car. I dont drive it, mostly she does so I guess she would know. Also, I think somebody must have changed this heater core before, I see broken pieces of hose down under the hood, inside the area near firewall, where the heater hoses go in.
Anyway, I think its working good now.

For those needing to know, Ranger was right, flush it if you can.

By the way, how do you get to those heater hoses to do a flush? Im thinking, would have to remove overflow tank, or get a skinny handed person in there.
 
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