240D Heat

[kchemers]

I have a 1976 240D with AC that doesn't work. I have not been able to figure out the heating system. If I turn the AC thermostat all the way to the left it shuts off the fan. If I turn the switch a liitle to the right the fan goes on but it blows cold air. I have the owners manual but it really doesn't answer any questions. Can someone please help!

[Fisherman]

Bill has some good thoughts on this particularly interesting setup. I had a dickens of a time figuring this out on my 115.

One other item I might add is that the A/C switch which you are refering to does in fact control the A/C blower but this is done via a switch that is mounted next to the center console (kick panel) on the drivers side. This switch is activated by a vacuum solenoid when you turn the switch to the on position.
The A/C swith really has two purposes and what I found on mine was that the first purpose which is acting as a vacuum switch is what controls two servos which direct the air flow either through the heater side of the system or through the A/C side of the system. This also controls which blower fan is on at any given time. A/C is the internal fan in the bottom of the console and "heat" is the blower motor mounted under the dash whcih gets it supply air fromt eh outside of the car just below the windshield. When this fan is on high or medium you can hear it distinctly from outside the car.
If this switch is not "fully" turned to the off position you may think that the heater is working but in fact the vacuum switch has not been actuated to power teh solenoids that turn the louvers (inside the console) to the heat side of the system.
If your A/C switch knob rotates after hitting what feels like the "stop" on the A/C "off" side, try pulling the knob out of the switch by tugging outward while gently moving from side to side. When you look into the switch with the knob removed, you will see an indentation that the knob engages to control the switch settings. Take a small screwdriver and gently try to move the switch all the way to the off position (couter clockwise). It is just past the point where you think it is off in most cases.
You should hear the vacuum solenoids move and the louvers inside the console clunk (as long as there is vacuum in the system) as they open and close.
With my vacuum leaks I could only do this with the car running and by watching the solenoid on the dirvers side move the control rod.
Hope this helps as I realize it is kind of lengthy. If you need more help let us know.

BTW - The center vent above the heater controls will always blow outside air no matter how high you have the heater controls. One way to test for heat is by opening one of the side vents. You can easily tell if it is warm air (A/C switch off) or cold air (A/C vacuum switch still on).

[P.E.Haiges]

Kchemers,

Check to see that the heat levers are turning the water valves on. Sometimes the wires break at the valves or inside the dash and the valves are not opened to allow hot water to circulate thru the heater core. You should feel heat on both sides of the valves if the water is circulating.

The valves can be turned by hand for heat until you get the wires fixed.

P E H