Help! c3 heater not working

[eoseitz]

I recently bought a 1974 Corvette L82. I hop in it this morning and attempt to turn on the defrosters. To my surprise nothing happens. I play with the controls and the blower comes on when I move the switch and the turn wheel to different position. However, hardly any air blows out. When I put my hand right by the vent and the defroster I can slightly feel air. I can hear the blower motor slightly too. I let the car warm up and the air still comes out cold. Drove to work with my head out the window in 40 degree weather.

Anyone know what may be causing this? Bad blower motor, switches, relay? This is my everyday driver now. This just wont work. otfl Any help would be appreciated.

 

[Vettehead Mikey]

There's several different systems involved.

The fan (blower) has three speed settings. Do you hear the fan changing speed at each setting?

There is a vacuum system to direct the air. It comes out at your feet towards the center of the car, the AC vents above the gauges or out the defroster vents on top of the dash. Does the air follow the movement of the control wheel?

The amount of heat available depends on the presence of hot coolant inside the heater core. Has your heater core been by passed possibly because of a leak? AC cars also have a vacuum operated shut off valve to stop coolant flow. Although they are designed to open with no vacuum (failsafe mode) yours might be jammed shut.

 

[eoseitz]

Thanks for the info. The fan does appear to work in at least two different speeds. However, the highest speed really doesn't blow all that hard. Is this normal on these cars? I can feel the air blowing out at the 3 different places (feet, vents, dash).

I'm starting to wonder if my heater core has been bypassed. The last owner swapped the motor for another l82. I wondering if he took the easy was and didn't hook the heater core back up.

Where would I find the AC cutout you were referring too. I know I no longer have an AC hooked up, but would the cutout still be in the system if the compressor pump is gone?

 

[Vettehead Mikey]

Sounds like max. speed on your blower is not working, but you would rarely need it anyway.

Take two seconds to open the hood and see if the heater core cooling lines are attached or not. One comes off the water pump, the other from the intake manifold. Both led to the heater core located in the passenger side of the firewall. The AC shut off valve is spliced into one of the two lines. It has no connection to the AC compressor.

I saw a post by you on 'that other' Corvette website. You need to get a new thermostat too. The car should not run cooler than the first line on the gauge which I think is 180.

 

[Evolution1980]

Could it be something as simple as a mouse setting up shop in his heating system? Wouldn't be the first time I've heard the story...

 

[eoseitz]

Turns out the heater core is not connected. The guy I bought the car off of said it's always been disconnected. Go figure. This should be an easy fix. I'll probably check the blower switch to see if the high fan speed terminal is corroded.

I did some research and it looks like you can test a heater core for leaks by covering one end with your thumb and sucking on the other. If you lose vacuum it has a leak. Does this sound reasonable? I guess if it doesn't hold vacuum it would have to have a whole in it. Will I need to tear out my dash to hook the heater core lines back up?

 

[Vettehead Mikey]

Well, that's progress. The connections for the heater core are on the engine side of the firewall but are real pain to reach on an AC car. The fact that the core has been deliberately bypassed by the previous owner is not a good sign, be prepared for a leaker.

 

[damoroso]

The hoses connect in the engine bay, not inside the car, so that's a good thing. Deffinetly check the core before you conect the hoses though. Remember, it's a little radiator and only needs to hold as much pressure as is on the radiator cap. Making sure it holds vacuum would accomplish the same thing as a pressure test, but I'm not sure about the "suck" test....doubt I'd do it that way....

I'd bet the core was bypassed for one of two reasons. First, it may have been leaking inside the car (it'll leave a puddle on the passenger floor board) or it was bypassed because it was always blowing hot air inside the car. That's a hole 'nother story.... and likely not the heater cores fault. It usually the heater valve, and or vacum actuators...it can be challanging but certainly not impossible to get working correctly!

 

[Evolution1980]

If you are going to be digging into it enough where you have to get to the core, you might just consider replacing it. They go bad. And yes, they are a PITA to replace if everything is already buttoned up on the car. "If you're already there and you have access to it..."

 

[eoseitz]

Where exactly are the connectors under the hood for the heater core. Unfortunately I do have an AC vehicle. I see two random hoses hanging under the car. They are about the size of water hose. It looks like they are under the heater blower box. Could this be them?

 

[73shark]

Probably as they come out under the evaporator box.

On A/C cars, the HI blower speed was controlled by a relay due to the high current. This relay was mounted on the evap box. Usual failure mode is burned contacts that won't pass the current. I've restored mine by removing the relay cover and cleaning the contacts. Or you can replace the relay. If you aren't going to use the A/C or drive in really cold weather, then you probably don't need HI speed anyway.