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No Heat


AaronM

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Hi,

Where do I start? Winter is coming fast :unsure: ! My A/C works great, but when I put the heat on, all I get is air from the fan, no heat. I have a factory service manual, but I didn't see anything in the diagnostics section. Where should I start? I hat to be cold, haha!?

Thanks!

Aaron :D

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18 Year Old Male

Black 1992 STS 4.9L

90,XXX Miles

Flowmaster 80 series muffler :D

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see what the classic says:

First thing is to check the coolant level. Don't trust the coolant recovery bottle. Take the radiator pressure cap off when the engine is cold. The coolant should be full to the top of the cap...in fact, you will probably spill some taking the cap off if the system is full. If not, or the coolant level is low in the radiator, then refill with 50/50 coolant/water and replace the cap as it is failed and not allowing coolant to be pulled back into the radiator.

Are you sure that the heater core has good flow? Feel the hoses on a cold start as the engine warms up and they should warm up with the engine...after it runs awhile the hoses will feel hot even with little or no flow.

Make sure the heater core is not plugged. You can take the two heater hoses off and flush with a garden hose to make sure the core is flowing and not plugged with gelled coolant or debris.

There are two main control doors in the HVAC system. One, the "up-down" door, controls the air delivery to the defrost or AC or heater outlets. That seems to be working OK>

The other door is the "air mix" door and that door controls the temp. That door may be stuck, or the actuator controlling it may be failed. you can check the position of the airmix door in the onboard diagnostics. The first thing to do is to check the onboard diagnostics for codes. If there is an air mix door failure it will likely set a code F40. Simultaneously press and hold the OFF and WARMER buttons until the onboard diagnostics activate. Read off the codes on the DIC.

After the codes read off the system will display .7.0 At this point press the OUTSIDE TEMP button to go to BCM DATA. The system will display F.8.0 use the LO and HI button to scroll thru the BCM DATA parameters to find P.2.2 which is commanded air mix door and P.2.3 which is the actual air mix door position. The two should agree. If they don't then the air mix door is stuck or the actuator is failed.

You can "jog" the air mix door by cycling the commanded temp from the highest possible setting to the lowest possible setting. Wait for a minute or so at each max temp setting and go back and forth several times. The max temp settings will automatically command the air mix door to the extremem settings either way which may unstick it.

bbobynsci

The saddest thing in life is wasted talent

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Thanks for the replies! I am going to change my coolant this weekend. I will have to do some poking around then ;). Thanks again for the help Larry,Adallak, and Guru!!!

18 Year Old Male

Black 1992 STS 4.9L

90,XXX Miles

Flowmaster 80 series muffler :D

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I have just checked out my air mix doors via BCM Data. At 90 it should have been 100 and actual was 99, at 60 it should have been 18 and actual was 20. Good enough. It means my problem is the plugged heater core. Unfortunately, I live in a town house, there is no garden hose around to flush it out. Looks like will drive another winter without heat.

The saddest thing in life is wasted talent

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