65GGvert

My previous C2's have been a/c cars and had a heater control valve mounted in the heater hose and controlled by vacuum. My current non a/c car does not have this valve and looking at parts suppliers catalogs, they are only used in a/c cars. Can anyone explain to me how the pull for temp control on the dash controls the heat in a non a/c car before I start taking things apart? Mine seems to be on hot with the control in or out. Thanks for any help.

MikeM

On a "heater only" car, the heat control, controls the amount of air flowing through the heater core. Unfortunately, some of the air will bleed through and put hot air inside the car.

Just put a manual shutoff in one of the heater hoses under the hood to block off the hot water. Turn it on/off, seasonally.

The "heat" cable controls a door in the heater plenum. If that cable is disconnected or out of adjustment, it'll let in more heat than intended. I believe if you take the glove box out, you can see how it works.

65GGvert

Thanks, that's what I assumed. I was concerned because when I pull it to defrost, it blows very hot whether the temp is in or out. Does that indicate a problem or is it normal?

JohnZ

Diagram below shows the airflow through the standard heater. The "Temp" **** controls the heat door, which bypasses outside air around the core when pushed in, forces all airflow through the core when pulled all the way out, and inbetween it mixes outside and heated air to regulate the temperature of the output air.

The "Air-Def" **** operates both the air and defroster doors; the first half of travel of the **** controls the air door, which allows airflow to exit the case, and the second half of travel operates the defroster door, diverting output air into the defroster duct.

Hot coolant is flowing through the core at all times, regardless of control settings (unless you add a shutoff valve as MikeM noted, which helps a LOT). Each of the doors have foam rubber seals; when they deteriorate, you get lots of airflow leaks.

Bluestripe67

Putting a shut off valve can have unintended consequences. By not continuing too flow engine coolant all the time the heater core could possibly be stressed by the shock of hot coolant and cause it to leak internally or externally.....maybe! You probably need new seals on the doors and cable adjustment. GM had a reason for engineering this system as they did. Dennis

MikeM

Tell me how this works differently than shutting the hot water off on an AC system.

65GGvert

Thanks Mike and John, very thorough helpful responses. I will check it out, it may very well be ok as is. Thanks again.

Avispa

Then why aren't there watern shock problems in A/C cars with a shutoff valve? Because the inlet hose is onlt 5/8 inch, and the inlet pipe has its end with inwardly crimped flutes to slow the water flow.

Bluestripe67

65GGvert, ignore my previous dribble. I have managed to confuse things, so what else is new. My thought was mixed up with blocking off/bypassing a heater core, letting it dry out over time and then shocking it with hot water. SORRY guys! Dennis