Heater Switch Issue

[Buckner99]

1984 Nissan 720. I can turn my heater on 1 & 2 setting, but if I try to turn it on full blast(3) blower motor shuts off and it stops working. I don't know if it would be the blower motor itself or if its the heater switch. I've had experience with bad blower motors in the past but this one has me baffled. there are so many loose wires and connections by mine its hard to tell what goes where...

[datzenmike]

 

 

Has this ever worked and just stopped working?

 

If the other speeds work the we know the electric motor is good, heater relay is working and the fuses are good. I would suspect the fan switch.

 

Work the fan switch back and forth through 3rd speed to clean the contacts.

 

 

 

 

[Buckner99]

ever since I have owned the truck this has been the way it has worked. only 1 and 2 setting works. I assumed it was the heater switch as well. Looks like I will be going to the junkyard to find one. I have ran the switch back and forth every time I go to turn the heater on but I'll try some more. I appreciate your quick responses..

[datzenmike]

The contacts have a grease on them that gets hard and dirty so 40 or 50 tries. Take it out and look at it. WD-40 and an old toothbrush.

[420n620]

does the 720's have a ASSY-RESISTOR like the 620's do ? If so, then that might be the problem. 

I'm referring to number 9 in the link provided.

https://www.carpartsmanual.com/datsun/pickup-1972-1979/electrical/room-heater

[datzenmike]

The electric motor is powered any time the ignition is on. To turn the fan on the heater switch selects 3 paths to ground. One is through two resistances for the slowest speed, the other is through only a single resistance to ground and for full fan speed no resistance and straight to ground. As there are two slow speeds, power is available and the switch is selecting the proper resistance coils. Only thing left is the switch connecting the ground.