Wendell Allen

And I'm hoping it's the same for all of these years.

With winter setting in (as much as it can in Houston, anyway), I decided I better get my blower motor back in operation again. And in doing so, I've found that our car's harness, where it hooks to the control in the center console, isn't wired according to the factory service manual. So instead of drawing out schematics as it should be and as it really is and just confusing people, I'm thinking that if you can tell me how the thing should work, that would help me fix it.

According to the NCRS's performance verification manual, assuming I'm reading it correctly, as soon as the left thumbwheel is put in either the a/c max, a/c norm, or bi-level position, the blower should kick on in low. The implication being that this is the case even when the blower itself is set to the off position. Is this correct? If not, what does your car do when going through this scenario? I'm especially concerned about what your car's blower does when these functions are selected and the blower switch is in the off position.

What the manual doesn't address is how the blower reacts in the vent, heater, or defroster positions. The control actually has a seperate switch that is underneath everything that is for the blower itself. My question for these functions is: When the left thumbwheel is in the vent, heat, or defrost positions, and the blower switch is in the off position, does the blower in fact run in the low speed anyway?

As an FYI, as far as I can tell, all my wiring is as it came from the factory, yet still doesn't agree with the schematic in my factory service manual. If I hook the wires to the control up according to the factory schematic, and with the blower switch set in the off position, when I select anything at all with the left thumb wheel (other than off), the blower kicks on in low, then dies when I try to select any other blower speed! Also, I've verified that everything in the engine compartment and on the blower is hooked up correctly.

Tom454

I have found two things over the years-

1) The schematics are not always correct.
2) The wiring for 1968 to 1972 is not identical. Don't assume a 1969 will function the same as a 1970.

I recently worked on 1968, 1970, and 1972 wiring problems and had to use schematics specific to year and option to even get close to the problem.

Maybe if you post the year of your car, those with specific experience will chime in?

I have pics etc turned off because I have a dial up connection- so maybe I'm not seeing all of your info

Just a suggestion.

7vette2

Wendell,
On my '72 the blower motor does activate on low speed as you described when the left thumbwheel is moved to a function. (heat,def etc) I beleive that the switch is never actually "off" unless the thumbwheel itself is in the off position. The blower is always on "low" when a function is selected so I believe that part of the wiring is correct. The question comes down to why the blower dies when you call for higher blower speeds. Is it possible that your switch is bad? Have you tested the motor itself? Get back to us with more information and let me know how you make out.
Ben

zwede

I have a 71 with factory AC.

The blower will operate on low speed with the fan selector in "off", whenever the left thumbwheel is at a setting that will turn the AC compressor on. These are bi-level, AC, and MAX AC.

In vent, heater and defrost it is possible to turn the blower off.

The blower will always be off regardless of fan setting with the left thumbwheel in the 'off' position.

The HVAC control unit has 2 switches on the bottom. One is for the 'all off' setting, the other one is for AC clutch on/off (plus blower low speed). The switches are adjusteable so that they open/close when the thumbwheel is in the correct position.

Note that the blower-low-speed thing only makes sure that the blower is atleast on the low speed. This means that with the thumbwheel on bi-level,ac or max, the 2 lowest fan speeds (off and low) are the same thing. The 2 higher speeds still work normally (i.e. no difference with ac on or off).

The reason for this is to prevent the evaporator from icing.

Hope this helps,

Wendell Allen

Ding, ding, ding!! We have a winner!

I guess people weren't too picky in the 70's. This would have been a warranty claim in a second these days.

Marcus's thoughts on how the system should operate are correct. As far as I can tell anyway. Ben got most of it complete. But where Marcus states that in the vent/heater/defroster modes, I should be able to turn the blower off, this is the difference.

Where Tom hit it was in that the schematic isn't always correct. And I've found this to be the case in other areas.

So, where the schematic shows a wire going from one pole of the blower/compressor switch to the blower operation switch, the one on my car was wired incorrectly. So to correct my situation, I had to:

1) Change the above mentioned wire to the other side of the blower/compressor switch.
2) Reverse two other wires on the blower operation switch. I found this by trial and error.

Now my blower:
1) When the A/C control wheel is in either the a/c max, a/c, or bilevel position, the blower operates on low in either the off or L1 position, and then steps up from there as I move the switch to M1, M2, and H2.
2) When the A/C control wheel is in either the heat, vent, or defrost position, the blower is off when the blower switch is in the off position, and then steps up from there as I move the switch to L1, M1, M2, or H2.

Thanks a million guys. Between the 3 of you, you really put this together for me.

Here's one to ya: :cheers: :cheers: :cheers:
OK. Maybe three.