96 Tahoe Heater Only Blows Warm Air

[Laredo1307]

Did you pressure flush the heater core, that's a common cause of low heat from heater. Most likely heater valve was closed. When you did the flush and fill you should have had the heat on hot, and fan on . As the service manual references. the coolant is moved pumped under pressure by the water pump , as it heats and cools it will self bleed any residual air through coolant recovery cap.

No, I have not but I'm fairly certain now that all the air is out of the system. I did find that my quick connect was seeping out fluid so while I was at it I went ahead and replaced my heat control valve even though I tested that whole system with the solenoid and it all appeared to be working properly. Luckily I did replace it though because it literally cracked into pieces as I tried to remove the hoses.


My heater is working somewhat better but still not what I believe is correct. I typically see about 120F coming out of the vents. Every once on a while it gets to about 128F. I believe my problem is a bad thermostat. It appears to be stuck open or at least slightly open. It's an OEM AC DELCO 131-151 I installed new when I changed the radiator but it had been sitting in my garage for a few years. Either way I've been using Dash Command to watch the temp and it never seems to get above 189F. This morning on the whole way to work (30miles) it never got above 180F. Wasn't till I made it to the office and sat in the parking lot that it hit 189F but it never seems to fluctuate like it's opening and closing properly.

 

[someotherguy]

Are you judging your engine temperature off the dash gauge, or measuring it with an IR thermometer scanning around the intake/thermostat housing area? The gauges are rarely accurate.

Richard

 

[Keeper]

stuck open sounds right, or it is actually a 180 tstat in disguise

you guys use the heater in Houston?

 

[someotherguy]

stuck open sounds right, or it is actually a 180 tstat in disguise

you guys use the heater in Houston?

Yeah, I mean, sometimes it gets a little chilly..

You must be registered for see images attach

Richard

 

[L31MaxExpress]

No, I have not but I'm fairly certain now that all the air is out of the system. I did find that my quick connect was seeping out fluid so while I was at it I went ahead and replaced my heat control valve even though I tested that whole system with the solenoid and it all appeared to be working properly. Luckily I did replace it though because it literally cracked into pieces as I tried to remove the hoses.


My heater is working somewhat better but still not what I believe is correct. I typically see about 120F coming out of the vents. Every once on a while it gets to about 128F. I believe my problem is a bad thermostat. It appears to be stuck open or at least slightly open. It's an OEM AC DELCO 131-151 I installed new when I changed the radiator but it had been sitting in my garage for a few years. Either way I've been using Dash Command to watch the temp and it never seems to get above 189F. This morning on the whole way to work (30miles) it never got above 180F. Wasn't till I made it to the office and sat in the parking lot that it hit 189F but it never seems to fluctuate like it's opening and closing properly.

Even with a 180F it should still blow ~140-150F especially once the engine is above idle. With a 170F and my engine running 176F the heat would cook you out of the van enough that I reduce the temperature knob to half and the fan speed to low or the 2nd notch. Gently reverse flush your heater core to clear it of sediments. Beyond that one of the air doors may not be sealing and all the airflow may not be going through the heater core.

 

[Laredo1307]

Are you judging your engine temperature off the dash gauge, or measuring it with an IR thermometer scanning around the intake/thermostat housing area? The gauges are rarely accurate.

Richard

Using Dash Command to read the temperature coming from the sensor

Even with a 180F it should still blow ~140-150F especially once the engine is above idle. With a 170F and my engine running 176F the heat would cook you out of the van enough that I reduce the temperature knob to half and the fan speed to low or the 2nd notch. Gently reverse flush your heater core to clear it of sediments. Beyond that one of the air doors may not be sealing and all the airflow may not be going through the heater core.

Yeah, I check my mode actuator and it seems to be working properly along with the others.

Yeah I should have flushed the heater core this past weekend but plenty of fluid drained out and I didn't really see any sediment. Going to replace the thermostat tonight.

 

[someotherguy]

Using Dash Command to read the temperature coming from the sensor

This is subject to error due to incorrect reading from CTS. Bad sensor, high resistance in ground connection or wiring, etc. Not saying the info coming from it is bad, but it has a much higher probability of being bad vs. a direct reading. The CTS operates off resistance just like the sender for the dash gauge. Higher resistance = colder reading. Extra resistance added due to sensor or connection issues = falsely colder reading than actual temp.

Richard

 

[Laredo1307]

This is subject to error due to incorrect reading from CTS. Bad sensor, high resistance in ground connection or wiring, etc. Not saying the info coming from it is bad, but it has a much higher probability of being bad vs. a direct reading. The CTS operates off resistance just like the sender for the dash gauge. Higher resistance = colder reading. Extra resistance added due to sensor or connection issues = falsely colder reading than actual temp.

Richard

Possibly but it’s a brand new sensor as well. Just replaced it a couple months ago. I can try putting the old one it to see if that makes a difference. I don’t believe anything is wrong with it.

 

[someotherguy]

Possibly but it’s a brand new sensor as well. Just replaced it a couple months ago. I can try putting the old one it to see if that makes a difference. I don’t believe anything is wrong with it.

Just saying, it may be reading correctly, but you don't know unless you confirm via other means.

Richard

 

[Laredo1307]

Well I'm back and I still can't solve my heater issue. I replaced my T-stat which does seem to be operating better than the old one. I also replaced the temp sensor as well. The heater seemed to be blowing warmer and was reaching a steady 130F when cruising on the highway. But that was with warmer temps outside. Now that we're experiencing freezing temps my heater is struggling to get luke warm.

Today I flushed the heater core going back and forth flowing water through each side. In the end the water ran through clear with no observable obstruction. I let my truck get up to operating temp and still no difference. The heater just barely blows warm. I felt the inlet and outlet hose to the heater core and they were both very hot.

As stated before I can see my blend door actuator rotating and I don't hear any noises or otherwise that would lead me to believe it's not working. The one thing I am questioning is if it's clocked appropriately. I recently replaced my A/C control module with an aftermarket one because the original was falling apart. Is there a procedure that ensures the blend door actuator operating appropriately if the Hot/ Cold switch was in a different position when I replaced it? My other thought is that the A/C module is faulty and I should just find an OEM one.