No Heat - '87 GM

[miamibob]

I have an '87 GM with a "no heat" situation. When I switch to the Floor position I only get cool air. I backflushed the cooling system and am now only running water so as to not waste antifreeze. The heater hoses are both hot at full running temp but sometimes the radiator hoses (especially the top one) are not hot. Something else interersting - as I checked it today while running I saw the top and bottom hoses collasped - then later open up to full diameter. Does this sound like air in the system or a thermostat problem? So are we talking thermostat, heater door or some other problem?? MB

[miamibob]

Any help on this one? I am especially interested in why the hoses are collapsing. They are only about a year old. Do I need to try and find ones with springs in them?? MB

[mattd424]

id replace the hoses if they are collapsing.was your cooling system real dirty when u flushed it?

[miamibob]

Actually the "output" was very clean! The hoses don't collapse all the time but it should never happen!

[miamibob]

Ok Folks! Went to work on it today - changed the coolant (not Heater) hoses, thermostat/gasket, by-pass hose, and the coolant sensor. Since I was already "in there" I did some of the above replacements (like the sensor). After the car comes to operating temperature, the radiator hoses (at least one) are warm/hot and the heater hoses (both of them) are real hot. I still have no heat. Would the next guess be the Heat Door Actuator (I already have a new one) or perhaps the sensor at the top of the dash (it has ATC). Maybe something else?? MB

[miamibob]

No thoughts on this at all????? MB

[miamibob]

A little help here???? MB

[miamibob]

So I changed the sensor and dropped the glove box to see the actuator door. I believe the door that controls heat is just in front of the blower. Is that correct? In any event, it opens and closes correctly so what is left to check? Can the Heater Core be bad even if both heater hoses are really hot? Someone HAS to have some thoughts on this one.....MB

[way2old]

Hey miamibob. Does the car heat up OK in the other positions and just fails to the floor, or all positions cool? If all positions are cool, I would look to the blend door. If it is just one position, look at the ATC unit. I believe there are vacuum ports inside the ATC head that control that function. Good luck.

[miamibob]

I need to check it better (ie. take it out on the road) but I believe it is cool in all positions and the air comes out of the proper place depending upon the control position. Is the "blend door" the one behind the glove box? I dropped the box cover and that door opens and closes correctly. Are you speaking of another door or is that it? MB

[way2old]

The blend door is the one behind the glove box. Are you sure the door is moving full travel when heat or cold is selected? It may be a pain, but try to remove the actuator motor, and see if moving the door by hand will give you any heat. If it does, replace the actuator. You should be able to feel and hear the door close when it reached the end of the travel.

[miamibob]

I pulled the glove box door (lowered it to be precise) and checked the blend door. It opens and closes the same amount weither I use the actuator or do it manually. In other words, it opens completely using both methods so I assume the actuator is good. Could the heater core be partially clogged even though the heater hoses coming to it and from it are very hot? If not where else do I look?? MB

[way2old]

Have you checked the radiator to see if it may be partially plugged also? If it is an 87 and never had proper maintenance, all the cooling/heating system could be partially plugged. Could also be a weak water pump that is not circulating enough coolant to properly heat and cool the engine. Does the temperature change when going down the road? You mentioned you were going to try that, but I don't see any results from that. The collapsing hoses could be from a weak radiator cap allowing the pressure to bleed off. Good luck.

[miamibob]

I changed the rad hoses, cap and thermostat. Also the temp sensor (at the engine) and the Air Sensor in the dash. As I said the blend door opens and closes completely in both directions. I back flushed the entire coolant system and the coolant came out clean but I changed it all anyway. Just curious, can the heater core be partially blocked even though both heater hoses that led in and out of it are hot? If weather permits I will take it out Sunday and see if there is any heat. There is no temp gauge - just the "idiot" light but I have never had the car overheat. What the exact temp is would be anyone's guess. MB

[miamibob]

Took the car out yesterday and in 85 plus degrees it is hard to really test the heater but it was coming out hot! I am not certain but one or more of my repairs seems to have worked. Many thanks to all that assisted!! MB