Can't seem to get any hot air for the heater/defroster. Can make the cold air move from defrost to floor but is very cold,feels like A/C is on. Compressor is cycling. Found white vac line near fan motor and replaced it,seems to have no effect. When I manually open or close the valve that the white line is connected to temp. does not change. Truck is a 96, 5.8 2wd that I have owned since new, so this is a new problem. First cold snap hit this morning and needed the defroster. Thanks in advance for answers.

 

There are 4 common conditions that produce this symptom:
1) VERY low coolant;
2) a previous owner/mechanic bypassed the heater core (usually because it leaks, so don't just hook it up & go driving);
3) the temperature blend cable breaks or comes out of its adjustment clip on the heater box, resulting in the temperature blend door not moving;
4) the blend door breaks off its hinge inside the box.

If the radiator is full & the hoses are connected like this:

...remove the glove box & observe the temperature cable while operating the dial. If the cable sheath moves significantly, it's probably out of its clip - follow it and try to snap it back in. It may take a few tries to get it adjusted correctly. If it doesn't move, the door is probably broken. Remove the heater core cover & look inside. Read these captions & follow the links in them:

.

 

Thanks Steve83 for your quick response and the info. Checked the temp. cables this morning, movement of the red lever is from about 6:00 to 3:00. This is really cold air blowing at defrost or heater. According to my a/c thermometer its about 38 degrees the same if I switch it to A/C. Do you think my next move should be take the air handler apart and check the door? Thanks again.

 

No, I think you should start with 1 & 2.

 

Sorry, I did not address 1 and 2 in my post. Radiator is full of a fresh 50/50 mix. Heater core hoses are still hooked up properly. Thanks again for any info.

 

Then yes: pull the heater core cover & look inside.

 

Ok. pulled the heater cover off,(not easy to see those hex screws if you wear bifocals neck won't bend back far enough) very clean inside no sign of leaking core.Can stick your hand over the left and feel the door move as you move the temp selector. Started engine and set controls for hot temp and defrost, cold air blowing thru core. Checked under hood, A/C accumulator and line coming out of it very cold. Shut off contols and left engine running to come up to operating temp. Heater core is not hot to the touch, heater core water lines are not near as hot as upper radiator hose. Thinking tomorrow night check water flow from water pump by disconnecting lines and maybe back flushing heater core. What do you think? Is the A/C supposed to be on when controls are set for heat? Or maybe just a water flow issue? Thanks again for your help!

 

A/C should run in all modes except VENT & FLOOR. Sounds like you have a restriction in the heater core circuit.

 

Could not look at the truck last night, go to work before daylight finish after dark. But this evening pulled heater core lines and flushed core both ways. Flushed hard lines on engine. Topped it back up with water,started it up brought it up to operating temp. Selector on Floor and Temp max hot, heater air not cold but not very warm either. Selector on Defrost and Temp max hot, A/C comp turns on and defrost air cold. Not sure if it will make a difference but i think i will replace the thermostat with a new 195 degree unit,don't think it can hurt. Just not sure what to do next. Seems to be alot easier to figure out why one runs hot. Thanks for any advice.

 

The heater circuit gets the hottest coolant available all the time, regardless of the t'stat. Either the engine isn't warming up (not likely), or the coolant isn't circulating (water pump impeller rusted away or slipping on the shaft), or there's a coolant restriction (impeller blades or sediment in the block or head), or there's an airflow problem (blower, evaporator, door). With the engine cool, pull the hose off the heater core that comes from the t'stat and start the engine. It should shoot water out like a garden hose. Reconnect it, and pull off the one going to the WP nipple - should be the same thing.

 

Replaced the thermostat yesterday evening, put in a 195. Did not make any difference.I am thinking it must be the impeller in the water pump. Engine will not come up to the usual operating temp, needle stays on the the O of normal temp. Usually reads between the R and M. Last evening after it had got warm the upper radiator hose was warm to the touch, but the heater core hose still felt cool. Maybe the water pump is not pushing enough water. Not looking forward to changing the water pump after reading about so many people breaking bolts in the block. This is just strange never had a vehicle that would not run hot enough, it's usually the other way around. Again thanks for your info Steve83.

 

I have a similar issue on my 93 F250. Fan runs fine, I can adjust hot to cold, but the blend doesn't work. Noticed the white hose to the HVAC damper motor under the hood was cracked away. Replaced it but still no blend. Tried manually manipulating the blend motor while the fan is on, but no change.
ANy ideas gents?

 

If the upper radiator hose gets hot, but the heater hoses don't, the WP is probably fine and there's a blockage in the heater circuit. Try pulling the heater hoses off with the engine idling, as I described above.

 

I hope you'll change the coolant on-schedule from now on.

BTW
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