Hello,

I am sure this has been asked and possibly answered somewhere on this thread, I was unable to find anything that matches what I am asking. I have a 1968 Oldsmobile 442, it has been restored sometime ago, garage kept, not a daily driver but does get driven. My heater in the car is original, the blower motor has been replaced when the AC system was upgraded. I have a 190 degree thermostat with a be-cool radiator. When operating the heater, I can switch between floor and defrost, however when I switch from cool to warm the temp does not change as it will blow cool all the time. Any ideas on what to look for? Thanks again for your replies and help.

 

You could possibly be low on coolant...I would check that first, or the t stat is stuck open.

 

Ok, so, to clarify, you cannot get warm air in the cabin when you call for it, but you have blower moving air, and you can change where the air goes.

This can be any of the following:
1. Your controls are not reaching the blend door. I believe it is a cable. When the car is off and quiet, does the slider feel like it has some resistance and can you hear a door opening/closing under the dash?
2. Or, the door is stuck, but the controls would feel weird.
3. Or, the blend door's rubber seal is toast.
4. Or, the heater control valve on the block is frozen closed.
5. Or, the heater core is clogged.

If the controls do operate the blend door, then a screwdriver handle rapped on the valve, it's on the back of the passenger head and the heater hose comes out of the block from it and goes into the firewall, might break it loose with percussive maintenance.

 

First things first, ensure the coolant is full. Make sure the engine is hot. Once the basics check out okay, time to dig deeper.

Feel both heater hoses, the both should be hot. One might be slightly cooler, but not a huge difference. If there is a huge difference in temperature, the heater control valve could be stick, or the heater core is blocked. I believe the heater control valve is suppose to close when vacuum is applied to the nipple, I don’t have a manual here to confirm. Other cars the control valve works backwards. Either way, the control valve is suppose to allow coolant flow with the climate control head in any position other than max A/C. You can check function with a handheld vacuum pump. The control valve needs to allow coolant flow for heat to work. Cold hoses means no coolant flow thru the core.

If there heater core checks out, it’s time to make sure the temp door actually moves with the temp lever. The temp door is mechanical, you should feel some resistance and hear the door as it moves.

 

68-69 heater control cable ends are notorious for breaking. See how they are cracked on this one:

https://www.ebay.com/itm/13324067495...hoCjcYQAvD_BwE

 

Are the heater hoses both hot? If so, look under the dash and see if the cable operated temperature blend door lever is moving.

 

Hello,

Both heater hoses were warm, cables for the vents work and the heater core was replaced about 4 years ago. What I found was the vacuum line from the AC/Heater control in the car to the Heater Actuator on the back of the block is bad, the vacuum line is original to the car. Trying to find replacements, any ideas?

 

If you can remove it, take it to your local auto parts store and you should be able to get the size and length you need.