Heater Problems

erandolph6 · December 10, 2009

2005 GMC Sierra Heating Problem. When at idle there is no heat coming out the vents even though the motor is at temperature. After driving a couple miles, I get heat but only out of the driver's side. Passenger side controls still blow cold. Any suggestions on a remedy. Winter in NY is going to get real cold for whoever rides shotgun

REV353 · December 10, 2009

I would grab both heater core coolant lines and make sure there both hot. This will help tell if your heater core is partially plugged, also make sure your coolant level is full.

mfennema · December 10, 2009

Make sure your coolant system is full. I had a leak once and I ran just low enough that it showed the engine was hot but it wasn't enough coolant to push it into the cabin heater circuit and heat the truck.

txab · December 10, 2009

^^^^beat me to it

erandolph6 · December 11, 2009

^^^^beat me to it

The Reservoir tank is full and I still have the same problem. Driver side gets cooking but the passenger is cold still.

REV353 · December 11, 2009

Sounds like your heater core is plugged, you can try an run some cleaner in your coolant or I have disconnected both lines before and taken a air hose and blown back wards through it. This did work, and I put some radiator cleaner through the system after. You still need to flush your whole system out before you reconnect your heater lines.

mfennema · December 11, 2009

^^^^beat me to it

The Reservoir tank is full and I still have the same problem. Driver side gets cooking but the passenger is cold still.

Just because your reservoir tank is full, does not mean that the system is full. If you have a bad cap and it leaks air, you can't create a vacuum to suck the coolant from the reservoir tank into the radiator. That aside, I am not sure exactly how the cab heaters are set up in these trucks and don't know how they are plumbed between. I assumed they were in series, but if you are getting heat to one and not the other, then this can't be the case. Sorry I can't help on this one I don't think.

56kz2slow · December 11, 2009

Is there 2 heater cores, or just one with blender doors to control both sides independently?

I had the opposite problem on mine, it was the driver that was getting cold air. The odd part is that I would stop the truck go in a store, come back and both sides would get heat.

Odd coincidence, the problem went away as soon as I fixed my 3rd brake light leak. My truck was only acting up in sub-zero temperature (Celsius that is, 0 is freezing point), with the leak, I always had humidity in the inside of the truck and I had frost inside the windows. My theory is that the extra humidity may have caused the blender valve to freeze, which may explain why I only got cold air when in the morning before the truck and outside temp warmed up. Again just a theory.

But it has been working fine for almost a month now, I even had an appointment booked at the dealer for it, but canceled it after the 1st week of working normally. I can just imagine the labour bill to take the dash apart to look at it. Took 7 hours on my friend's Jeep to fix something similar.