94 K1500 No Heat Issue

[Greggers]

Hello! I'm having a heat issue, and haven't been able to track down anything anywhere to help me out, hopefully you guys can point me in the right direction!

 

Basically.... My '94 Chevy K1500 (5.7L) has no heat. My coolant is full, my thermostat was changed 3 months ago, my Coolant Temp Sensor was changed about a month ago, my truck warms up normally, and stays just under 100, (just a sliver under halfway on the temp gauge!) the blower motor blows all speeds as it should, and I can change from defrost, to vents, to floor, or blend in between and they all work as they should. I've taken out my heater core and flushed it out both ways. All that came out was normal green coolant. (Even before I flushed it the inlet and outlet lines were both hot). I've checked the blend door actuator and all the gears inside are still lubricated and intact. I went from hot to cold and back on the heater control on the dash, and watched the actuator move and do it's thing. If I pull the bottom of the heatercore box off, I can feel hot air coming out around it.

 

The only way I can get luke warm air out of my truck, is if I hit the MAX button on the heater control (it shoots it out the vents on hi, and recirculates it....but it's luke warm!!)

 

So.... I ask you... Why is my heatercore hot and everything is seemingly functioning as it should, yet the only way I can get a hint of warm air is with recirculation? What do I need to replace or look at?! Please point me in the right direction!

 

 

Cliff notes:

 

'94 Chevy K1500 has no warm/hot air from any vents unless on recirc, and even then it's barely warm.

 

 

• Coolant topped up and clean.
  
• Thermostat changed 3 months ago.
  
• Coolant Temp Sensor changed 1 month ago.
  
• Truck warms up normally and temp needle sits where any Chevy of the same era (that I've driven) sits.
  
• Blower motor works on all speeds.
  
• Defrost/Vents/Floor all work.
  
• Heater Core has been flushed.
  
• Blend Door Actuator is fine.
  
• Heater Core has hot air blowing through it if I drop the bottom of the heater core box.
  

 

Much thanks,

--Greg.

[Greggers]

Update: I parked my truck and shut it off, and when I came out, and started it back up... one of the actuators started clicking like mad for about 45 seconds. I followed the noise, and it's the actuator that's right against the firewall behind the glovebox. (I think it's called the Air Circulator Blend Actuator?) Anyways, I took that out and opened it up, and all the gears are in good condition and nothing is broken. My Haynes manual isn't much help. Can anyone point me in the right direction as to what to do next? Is there something that controls the actuator that could need replacing? A way to align it properly, perhaps?!

 

Thanks!

--Greg.

[citydriver]

How is the airflow from the vents, can you feel it, does it have A/C? Is the evaporater clogged up with depris? leaves, dirt, pine needles,etc... It may also have an air pocket trapped in the core. You could try pulling the coolant return line from the hater core, or just install a Flush "T" and loosen the cap a little to vent the any air trapped in the system, while the engine is running (using EXTREME CAUTIION is advised) being carfull as to not getting hot coolant on you...Worst case scenario...Have the intake manifold gaskets been changed lately...where they installed incorrectly?

[sonoramike]

unplug the connector on the front of the AC compressor to temporarily eliminate the AC from the problem while troubleshooting your heat problem. if you have the defroster selected (knob turned to either straight defroster, or feeter/defroster) then the AC will cycle on every minute or so which could be your clicking. if the AC charge is low then the clicking will happen more frequently, mine did an on/off clicking cycle every 10 seconds or so.

 

got embarrassed at my mechanics shop yesterday when I couldn't figure out why all the clicking was going on and the truck would lose power. he said "you've got the defroster on" me:"no way" - turns out he was right, AC was coming on, truck would bog when the AC was on, AC compressor is leaking so charge is low.

 

If you've got heat in the hose heading to and from your heater core then you are getting hot coolant flow thru the core. either air is not being allowed to pass thru the hot core to the cabin, or the hot air coming off the core is being cooled by the AC