Ok so I have a 94 chevy silverado Z71 that blows warm air through the face vents on max/recycle only. Swith the "rec" off, and it goes back to cooler but not cold. Defrost, cool. Floorboard, cool. Only when the max is on will it blow warm air.

The truck is a hand-me-down from my dad who bought it new, so I know everything thats ever been done to it. Its had all the heating components like thermostat, water pump, radiator, fan replaced in the past. Heater cores been replaced 4 times because we ran through a batch that would leak after a few months.

I just recently had the coolant system flushed, and still the same problem. The heater core itself feels hot, as do the lines going to it. I can hear the temp door move throughout the range, and the air direction goes where its supposed to go (goes to defrost like it should, goes to floor like it should, etc.) And the recycle doors works right too.

What could cause it to only blow warm air in recycle mode? Is there another actuator im missing?

 

So after driving it again today, I would like to add the "warm" air I describe is merely lukewarm. Not hot by any means, and definitely not warm enough for the cold winter. Im guessing its only warmer because of the recycling of cabin air. Either way, im lost as to where to look next.

 

If everything is working normally, the most likely the air door seals have rotted off and is letting cold outside air mix with your heater air.

 

What temp of stat are you running in it. When the a/c is on will it go from full cold to hot. If you have under a 195 degree stat that is more than likely where your problem lies. On your truck if you pull out the cassette deck if it's still there the temp actuator is screwed to case in that area you should be able to see the shaft twist in increments as you adjust the temp.

 

The truck has a newer stock 195 temp thermostat that I installed last winter. I actually took the glove box out to get to the blend door actuator and it is working fine. I did however go ahead and take that actuator off and operate the blend door by hand and it feels and sounds like it is operating correctly. Still no heat to speak of really. Put the actuator back on and back to square one. I can see and hear the actuator operate full range.

Im beginning to wonder how hot should the coolant be going to the core? Could I possibly take one of the heater hoses off and tee in a temp gauge to check the temp there? If so should it be 195 or more or less?

 

The hose to and from the core should be too hot to hold onto.

 

Well that could be my problem. The hoses are pretty warm, but I can definitely hold on to them with bare hands. I just had a coolant flush, so maybe a tired water pump?

 

You probably broke the tab that holds the heater core tight against the case. I broke mine when working by flashlight. I had the same issue as you. Hope this helps

 

Wow I didn't even know there was a tab. When I changed that lower cover, the core kind of just flops around , so I figured that lower cover was what held it up in place.

 

Well thanks everyone for the help, but iamkeniff hit the nail right on the head. The heater core had fallen down against the lower cover, and wasnt being held up against the seals where the air comes in. So the air was simply blowing over the top and past the core instead of through it. So I made a makeshift fix to hold the core up where it should be, and now the heater works amazingly. Thanks again guys.