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The heater in my wife’s Tahoe has started acting up the last few days and it has me baffled. When I start it up in the morning to let the engine warm, the heater will blow warm air. After getting out on the highway, the dang thing starts blowing cold air. I took it out for a spin this evening in 70 degree weather and it did the same thing. The heater core isn’t plugged because both the feed and return lines going through the firewall are hot. The engine gets to operating temperature so I know the thermostat is working correctly. The coolant level is fine. I’m stumped at this point. Could it be the blend door actuator?


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Discussion Starter #3
Thank you, sir. I’ll give it a try.


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Hate to say it but head gaskets. Check the resivor tank in the morning before u start it. If there is still pressure it’s definitely head gaskets.
 

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Hate to say it but head gaskets. Check the resivor tank in the morning before u start it. If there is still pressure it’s definitely head gaskets.
What makes you think this problem is due to a blown head gasket? How would that explain the HVAC temperature dropping? With a blown head gasket the engine will consume coolant, and he said his coolant level is fine.

I had a similar problem with a 2002 Grand Cherokee, which was known to have issues with the blend doors. That sounds like the most likely explanation to me. Although I'm not sure this is good news as compared to a blown head gasket -- the repair costs can be exorbitant due to the amount of crap that has to come out of the vehicle to access the doors. I heard of repair costs for this problem with my Jeep getting damn near $2,000.
 

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Thanks for all the replies guys. I’m pretty sure it’s the blend door actuator because the rear will still blow warm when the front gets cool. It’s pretty intermittent too. It hasn’t done it in about 2 weeks.


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Does sound like the Blend Door Actuator- that is the one over the trans hump, and the easiest to replace.
 

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Does sound like the Blend Door Actuator- that is the one over the trans hump, and the easiest to replace.


That’s good to hear. Thank you, sir.


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Low on coolant, air pocket, or head gasket can cause the same symptoms. What does the temp gauge read when it does this?
 

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Low on coolant, air pocket, or head gasket can cause the same symptoms. What does the temp gauge read when it does this?


It’s done it at operating temp on down to just warm enough to heat the air. No rhyme or reason as far as that goes. I’m fairly certain it’s the actuator at this point since the rear stays warm when the front cools.


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