Heater only blowing cold air ?

[njonl]

My heater just recently started blowing only cold air on every setting. I took the glove box out to look at the control linkages and sure enough the temp adjuster linkage was off so I hooked it back up and it still wouldn't blow hot air. So now I took the hoses off of the heater core thinking that it might be clogged. I took an air nozzle and stuck it up the heater core inlet and blew some air through there and it seemed to flow freely. Next I stuck a water hose in there and the water seemed to flow through freely as well. I figured that wasnt the problem so I took the front piece of off the air box under the dash to look at the doors internally and all of them seem to be functioning properly with all of the vacuum hooked up correctly and working. Where should I look next ? Sorry that was a long one but there are a lot of details. Thanks!

 

[njonl]

And I forgot to add that I have a hose running from the top port of my water pump to the bottom nipple of the heater core and the top hose is running to the top of the radiator.

 

[njonl]

bump anybody ?

 

[ryoken]

radiator is full?

 

[JEBSR]

Is the engine warming up properly? If so once the engine is at operating temperature feel both lines at the heater core. Both should be very hot and the same temp. Let us know what you find.

 

[babyburb]

stuck thermastat? Fixed my problem. cost $10
Good luck!

 

[85-m1028]

And I forgot to add that I have a hose running from the top port of my water pump to the bottom nipple of the heater core and the top hose is running to the top of the radiator.

the routing should go from the crossover to the top "nipple" and the bottom one goes to the radiator. make sure those hoses are tight on that heater core side and check for leaks after you install them..

 

[diesel4me]

Mickey + Minnie??..

Maybe mice built a nest next to the heater core,blocking the flow of heat into the cab?...trucks that sit any length of time around here usually have a few rodents living in the heater ducts!... ....

 

[neverendingproject]

Vaccum leak could cause teh heater vent not to open, and consequently only blowing outside air.

 

[njonl]

Ok here is an update for everybody that asked me questions.. I touched the heater lines and only one is warm and it is the one coming from the water pump. It seems as though all the correct doors are opening. I hope the front part of the heater box open so I can see the doors opening and closing. I'm running out of ideas.. and it's getting cold!!

 

[JEBSR]

If only one line is getting warm then the heater core is clogged. Both lines should be the same or within a few degrees of the same temp

 

[gmc4cw]

is the hose hotter close to the pump then it is by the heater core. I would unhook the hose from the radiator and run the truck to see if it is pumping through the core. maybe the water pump is clogged up at the port and only a trickle is getting through.

get the truck warm first so that you know the thermostat is open. get the hoses loose before you warm everything up so you don't have to fight with hot parts. good luck, don't burn yourself.