1983 300td no hi blower climate control
 

Hi all
I have been tearing into my climate control issue to get ready for winter. I have bypassed the center vents and do not have any vacuum leaks now. However, I cannot get the fan to switch on the high setting when I push the button. It works with automatic on the bi-level and floor settings and on low for all settings. I have ruled out the control unit as i have tried three different ones I was able to get from friends.
I just hooked up the coolant to the heater core (I bought the car from FL and it was disconnected). I thought maybe there was not enough heat to switch the relay on. It still does not work, however.
Is this maybe the big metal relay box behind the glove box?
Oh yeah, the fan is operational as I plugged a spare in and it does the same thing. There is no current to the plug when I turn on the high switch. Right now we are running the heat by just leaving the bi-level setting on and pushing automatic on the fan, basically using the fan switch as our heater switch.
Any ideas?