1979 620 KC Heater assembly

[Joshua]

Hello ratsun community,  I'm sure this has been covered already but I'm not finding what I need to know. My 79 620 k.cab's heater isn't fully  functioning.The defrost nozzle/vents for the windshield work, and blow heat.The Rt./Lt. Vents ,close to the  doors do nothing, no heat and no air flow.Finally, the vent(s)  below the dash (center) , where you  push the know in for vent Does work,  however NO heat ,even though I've got heat Uptop through the windshield vents.I am pretty sure that in the past ,the vent below dash (center), when pushed in I would have  heat there as well..Could this be do to a resistor or perhaps the heater core itself?..I am contemplating removing the whole  heater assembly to inspect, clean,lubricate cabling and or refelt , blah blah ect.Mabye  I'm imaging heat coming from the lower vent, it's been a while and the side vent never worked.This 620 is NOT A/C equipped..Thank you wise ones..

[datzenmike]

The L&R vents close to the windows are outside air vents only. There is a small knob below them to pull out to activate, in to close.

 

The large knob in the center of the heater is pushed in for air (hot or cold) and pulled out to close.

 

Of the slide controls....

 

The top slide in the far left position, allows cool outside air out the center grill of the large knob is pushed in, otherwise no air in at all. In the center position allows air to the defrost vents and out the center vent if knob is pulled out. Between center and far right allows a mixture of defrost and heater air out to the left and right bottom and out the center grill if selected. In the far right position primarily delivers heated air to the left and right bottom vents and the center if selected.

 

The bottom slide selects from cold (left) to hot (right) and closes the heater hose valve when in the far left position.

 

 

So if you have heat in any position, then the heater core is working and should deliver as described above. Any failure is likely a cable control has become disconnected or out of adjustment.

 

There is a flap gate that varies the air to the defrost and cabin. If just defrost then the gate is not fully opening. Watch it while moving the top slide control from the center position and to the right.

 

The resister is in the air stream to keep it cool and it drops the voltage to the fan motor to slow it.

 

On the right side there is a water valve. Make sure the bottom slide control opens and closes it fully by watching.

 

The top surface of the heater core can become blocked by leaves and maple keys and reduces air flow even if the rest of the heater is working properly.

 

With the wiper arms removed and hood up you can get at the screws that hold the plenum cover on. This is the part with the louvers and wiper arms sticking through. Leaves, pine needles and maple keys can collect to the sides and obstruct the plenum drains. This can cause rust and at worst water can slosh and fall into the heater inside the cabin.   

[FrankRizzo]

I'll add to Mikes thorough explanation...that the fan is controlled by the lover lever by pulling it out, away from the dash to force hot air out of the heater box.

.