No Heat

I have 1995 GMC Yukon that does not blow any heat. First the facts, My Air Conditioning is all brand new and works great, Installed new heater core, new blend door actuator, new heater control valve and solenoid. I flushed out the heater core. When the truck is up to temp all of the hoses feel hot except the bottom radiator hose. My next thing that I was going to replace was the thermostat. I've noticed that the temp doesn't really rise up then lower down to a normal operating temp. My question is there any other thing that might be the problem. The fan blows great but when I try to switch to heat nothing but cool air. Do you think the control panel inside of the truck might be at fault. Thank You for your input.

Could definitely be the control panel, I've heard of them failing before. I'd try the thermostat first, though. The fact that your bottom hose isn't getting makes me think there's something blocking the flow of coolant.

As df2x4 said, throw a new thermostat in first. With the coolant hose like you're saying, that's the first thing I'd do.

I had to replace my HVAC control panel a few years back but my problem was it wouldn't do anything but full-blast or off, no in between. I found out the circuit board had actually melted somewhat. Just throwing my $0.02 in. From everything you're saying, it's sounding like a thermostat.


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Thank You

Update - So I replaced my thermostat and I also went ahead and replaced my radiator. Thermostat worked like it suppose to and radiator worked great. My old one was a little more beat up than I thought. All of the hose are getting hot now, but still no heat out of my vents. So I guess the heater and a/c control panel is next. But i do have a question, is the another door that's by the heater core side that diverts hot and cold air. If there is what is it called. Any help is much appreciated.

Could be the blend door actuator

I'd check your HVAC control unit, the thing under the radio. I've had to replace mine once and now I have to replace it again because it will only work on High after I wiggle the wires behind it.

Which door actuator did you replace? The mode actuator is near the gas pedal, controlling air distribution to floor/panel with the temperature actuator being on the front of the case kind of near the ashtray.

On the actuator, there should be a dial with a slot in it that rotates as the damper position changes. If you can see it, see if it rotates.

Here are the diagnostics for the temperature door actuator on a 1998, it may work for your 1995 but I remember reading that the control panel changed for 1996. Hope it helps.








Connector C3...





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Thank you. I changed the blend door actuator. Yes I can see it rotate. This will help thanks again

Just saw this,... First, its VERY strange that the lower radiator hose isnt getting hot at all and that your temp isnt "changing" with the opening and closing of the thermostat, especially at this time of year. The lower radiator hose should definately feel pretty warm, once it gets to temp, albeit cooler than the upper hose.

- Is the lower hose maybe collapsing under throttle??? It does happen, especially if the internal anti-collapse spring broke, is missing, or the hose is weak.
- Is your engine running hotter than normal on the road?
- Maybe the thermostat is upside down or faulty? It happens to the best of us.
- Did you change the Water Pump? Your water pump have an air bubble? Might also be a bad impeller, which causes cavitaion inside the water pump, instead of actually pumping water into the block. (Remember, a lower radiator hose pulls cooled AF from the bottom of the radiator.)

A bad HVAC could explain a cold heater core hose, depending on the type of control valve setup on those hoses, but it shouldnt create any noticable issues for your lower radiator hose.