If the blend door on the heater box is struck or out of adjustment - then no heat. Or the cable is out of adjustment or broken.

 

Ok,
The hose from the block to the radiator is considerably hotter than the hose from the block to the vacuum valve and from the valve into the heater box.

 

Is there an easy way to reach the door or check the cable without disassembling the whole dash? I found a youtube video which looked like there's a lot of work to that piece which I'm not ready for quite yet. (Getting there but don't want her in pieces quite yet ).

 

Try the selector in defrost position
With my 75 the defrost position works much better to heat the cabin
I should look into it

 

In Defrost there's barely any airflow, just like with Heater or AC. Almost like the airflow is blocked.

 

I know you have a '79 but in my '71 owners manual it says to use a 180. If you have the manual look in that. I bet it says 180 (or higher).

 

I run a 160 stat in my 71 - no heat issues. It was 30 yesterday.

If both hoses are hot - the issue usually is in the heater box or controls. . If the hoses are not hot - it's usually the heater water control valve. Easy to test with a vacuum pump. (mitymite) . No Vacuum it should be open. (if I remember right)

I find the blend door is usually stuck, the cable is off or the thumb wheel is not opening / moving the cable. Thus you have outside air entering the car.

Pull the passenger side lower dash pad and check the heater controls - if they are not working or out of adjustment - there is your problem.

When I opened up the heater box on my 71, as usual I found it half full of debris - leaves /pine needles, twigs etc. This will cut down on the heat / air flow.

If it's and A/C car pull the resister for the fan motor and using a inspection camera CAREFULLY look into the heater box, IF clogged - You can clean out the box if you carefully use a plastic hose on a shop vacuum to suck out the debris. I did a friends 70 and the heat returned. IT was 3/4 full.

I have done a few cars for friends and most had the controls out of adjustment or stuck / frozen. This is the first thing to check.

I did find one car with the fan clogged with debris. Again the camera came in handy. As did the hose on the shop vacuum to clean it out.

 

Do you have a good pic or video showing where to pull the resistor and check for the clogged box? Same for where the heater controls are at as well as the thumb wheel? I'm starting to learn from googling and youtube but there's a lot of mis or cross-leading information due to various models, etc. With the winter coming on I will have time to crack open the dash but don't want to break anything worse or just do it wrong and not know what I did.

Don't take it wrong, I want to do a lot my self and there are some things I know I can't do yet ( install Cats or anything requiring a lift ) but I am still learning my limits too.

 

If the heater hose is strictly warm then you likely don't have water flow to the core. If your confident that the hose valve is working correctly then the heater core may be plugged and if so the hoses will not get to full temp but may be warm close to the motor but cool at the fire wall where the hoses enter the heater core. If the core has un-obstructed flow the hoses will be hot, as hot as the as the return hose to the radiator from the motor.

To check flow you can disconnect the hoses to the heater core and attach a water hose and test the flow through the heater core. It's easier to disconnect the hoses at the water pump/intake and use a 5/8" hose splice to connect the water hose to one of the hoses.

It could be that the temperature control door may not be opening also but your statement that the heater hose is only warm has me considering the possibility that the core may be obstructed.

Neal

Neal

 

I'll try to get hoses hooked up.

To test the Heater Control Switch has vacuum the switch should be open allowing flow? One thing I noticed when I checked the heat yesterday ( Make sure you're careful of hot heads.......... ), it seemed there was good vacuum on it when I had the switch set to Heat and defrost. I'm not sure the min/max but I could put my finger over the hose and feel some vacuum preasure.

 

I've got a 180 in it now, the engine temp is heating properly, still nothing through the vents so I'm looking at verifying the Vacuum switch, door and cables. I really would rather not pull the core.

 

Also, double check your core for proper flow. Disconnect the hoses at the heater valve and run water through them. If it comes out the other end you are good. Those things get clogged after years.

I replace the heater core on my 82 a few months back. It was not a hard job but definitely a PITA. The bonus was that while disassembled, I was able to check all valves, hoses, cables and such. When I reassembled everything was perfect. AC, Heat...everything worked as factory.

I did it over 4 nights after work for total of 10 hours. If plan on keeping the car, I'd suggest just sucking it up and going for a rebuild--- once you take everything apart for an inspection, you only have 4 mounting bolts, a couple of cables and the hose disconnect to go!

 

Found some new info while getting the Carb fixed. The AC motor kept cycling on and off even when the switch was in the off position. I also noticed when I moved the selector from DEF to Off, there was very little resistance as if the cable isn't connected. So I'm thinking I'll start there this weekend and see what I can find.

 

Have you verified that the heater hoses are still connected? Not uncommon to jumper or block off the heater hoses if the heater core leaks Look for a simple solution... Hey, I know your car is only 37 years old, but this might have been done 20 years ago.

 

Yeah, they're still connected and I don't see any place it looks like they're blocked or plugged off.

 

If you take out the glove box you can see where the cable operates the door for the heater.

 

Do the hoses get warm when the car is running and the heater is ON? If they do not, then the heater valve is not permitting the warm coolant into the heater.

 

I pulled the glovebox and I can see the cable moving on the hot-cold selector and hear the door open/close.

I can not see where the AC/Def/Vent/Heater switch goes but when I slide it I feel almost NO resistance. My 89 Jeep has a LOT more when I slide it where the Vette feels like it's not connected at the back and is just stuck in the "OFF" position.

Something is also keeping me from removing the center console to look at the cable on the back and see if it is loose. Anyone have a diagram with connectors or a good video that shows how to remove the center console on a 79 C3?

 

Mines like that now. Did it years ago when my heater core started leaking. I lived in Tx at the time and didn't need heat anyway and it stayed that way. I'll fix it someday.

 

Ok, I pulled out the console. The Selector Switch for Off/AC/Def/Heater is electrical, not a mechanical cable like my Jeep. The mechanics appear to be working right. Now to track down where the far ends come out and check for power at those connections.