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LMC Truck



Username Post: Heater blowing cold air        (Topic#348565)
bubbanm 
Forum Newbie
Posts: 88

Loc: Tennessee
Reg: 04-14-08
12-05-17 01:47 PM - Post#2716971    

Hi Everyone,
Back in the summer I replaced the drivers side door blend actuator because I had hot air coming in on the drivers side of the truck. Now its cold weather and the heater is blowing cold air on both the driver and passenger side. It does not do it all the time but sometimes it does. I have the dual climate control and both sides will be blowing cold air when they are set on hot. Sometimes it works fine but other times it is blowing cold air. Any ideas what might be causing this on my 04 Silerado ?



 
LMC Trucks
454cid 
Frequent Contributor
Posts: 2467
454cid
Age: 44
Loc: West Michigan
Reg: 02-18-12
12-05-17 02:56 PM - Post#2716975    
    In response to bubbanm

  • bubbanm Said:
...the heater is blowing cold air on both the driver and passenger side. It does not do it all the time but sometimes it does.....Sometimes it works fine but other times it is blowing cold air.



I don't know the GMT-800 HVAC system, but in general a vehicle won't produce heat consistently if the coolant is low.....it will come and go. You might check to see that the cooling system isn't super low....does your truck even have a radiator cap, on the radiator?

If it's low, and you have a gauge, the temperature will rapidly climb from cold, to beyond normal, and then drop below normal when the thermostat opens.


99 K3500 RCLB


 
bubbanm 
Forum Newbie
Posts: 88

Loc: Tennessee
Reg: 04-14-08
12-06-17 09:50 AM - Post#2717065    
    In response to 454cid

You hit the nail on the head. The coolant was low. I don't have any leaks since I park in my garage I would see them. The coolant must have evaporated since I last changed it a couple of years ago. Can that happen?



 
someotherguy 
Moderator
Posts: 28463
someotherguy
Age: 47
Loc: Texas
Reg: 08-01-03
12-06-17 10:36 AM - Post#2717071    
    In response to bubbanm

No on the evaporation...sure hope you don't have the infamous Castech heads issue with your engine.

http://ww2.justanswer.com/uploads/Bluegorilla/2 008...

Time to do a pressure test of your cooling system, see if you can determine where the leak is. Obviously do it on a cool engine so you're not opening the cap on a hot, pressurized system. See if it will hold around 16 psi since that's likely the rating on your cap. Don't over-pressurize it as you can damage the heater core or radiator.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
454cid 
Frequent Contributor
Posts: 2467
454cid
Age: 44
Loc: West Michigan
Reg: 02-18-12
12-06-17 01:11 PM - Post#2717093    
    In response to bubbanm

  • bubbanm Said:
You hit the nail on the head. The coolant was low. I don't have any leaks since I park in my garage I would see them. The coolant must have evaporated since I last changed it a couple of years ago. Can that happen?



It could be a small leak that evaporates when it contacts the outside of the hot engine.....or possibly the Castech head issue. I don't know much about the heads since I don't have an LS engine, However.


99 K3500 RCLB


 
LMC Trucks
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