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Hello,
I have a 2003 buick lesabre limited.. that blows cold air instead of heat. System was flushed about 5 times, we checked the actuator doors- seems to be doing its job- we then changed the heater core, and bled/burped the system to get any air locks out. After it was put together heat worked great for 3 days and now it's back to cold air again.... (oh water pump was also changed) only thing left that we did not change was the thermostat... though, I'm not sure it's the cause. Could another air lock happen days after everything was replaced? This has been a nightmare to figure out!


   
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Location: Oregon
without specialized tools it may be difficult to run this problem down. Verifying coolant circulation vs. blend door operation to find out why you don't get heat out the vent could be a problem. As far as your thermostat, how is the engine temperature> Does the engine get up to normal engine temp? Should be right around 210 degrees warmed up. If the engine temperature is normal then it is not the thermostat.

After the engine is warmed up and you are trying to get heat into the cab, check the two hoses going into the heater core. are they both hot? There should be a hose that comes from over by the water pump. That should be the hot line into the heater core. The other hose that should go back to the engine should be the heater core out. If they are both hot the the heater core should be hot too. If one is hot and the other not then you could have a blockage in the heater core. (Air lock, plugged up, whatever, even a new heater core) If both hoses are hot then you need to revisit the blend door operation.

With the key on and the engine off, the fan on the lowest setting, move the temperature from the coldest to the warmest setting. Then listen to hear the blend door motor moving. It is an electric motor that moves the door from end to end. I would do this with a scanner and look at the reading as the motor moved or not. There should also be codes for a motor/actuator not moving correctly. This will not set the check engine light because it has nothing to do with the motor but it should be a code stored in the HVAC system.

if you disconnect the battery voltage to the HVAC module for more than 60 seconds and then reconnect it it will do a re-calibration of the unit. Then it might work for a while again because of the reset. But if the actuator is bad, after a while it may stop working again. If you take it to a shop they could scan the HVAC to see if the actuator is a problem. If the shop has a thermal imager they can easily check the heater hoses for temperature in and out.

Let me know what you find out.


   
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