Dash air fan switch?
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Dash air fan switch?
I know this has been covered before but search command wasnt helpful. Need to understand how the fan switch on dash [manual style not digital] controls the dash fan. The switch on my 87 only works in the high mode, not low or the two intermediate settings. Do you think its the switch itself or the relays or resistor coils on/near the fan motor--so how best to go about diagnosing this?
Safety Car
Joined: Apr 2011
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Its a process of elimination. Because there ARE multiple points where this symptom can originate, there are specific test to perform. This is why the $100 investment in a FSM will save you lots of time and aggrevation by following the GM trouble tree charts directly to the source of the problem.
Without the FSM, you;re guessing. You could get a DVM and test the switch, or test the relays to see which was not operating,or start buying parts and hope for the best.
That FSM pays for itself pretty quick.
Without the FSM, you;re guessing. You could get a DVM and test the switch, or test the relays to see which was not operating,or start buying parts and hope for the best.
That FSM pays for itself pretty quick.
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Appreciate the input--I have the FSM for the 87 and will begin the search. Was hoping for a "silver-bullet" based on symptoms but as with most things on this restore project, I'll just have to grind it out....thanks again....
Race Director
Joined: Aug 2007
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From: Whitefish Falls Ontario
St. Jude Donor '08-'09
The main thing you need is a multi-meter, if you find the wiring diagram for the blower and start checking voltage to the relay with key in run and function control in any position, blower switch in any position other than high, you should get 12v through the resistors, on my 84 its a dark blue wire. You should get the 12v on a black/red wire to the blower motor.. The relay only operates on high speed so the other speeds go through the resistors and the normally closed contacts of the relay.. 
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Kind of a process of elimination but since the hi-speed relay is working--apparently and based on what I have seen for the old style wire resistors being pretty durable, it would seem that the switch is the likely cause. Given how difficult it is to tear apart the dash to get at the switch, I was hoping to narrow the root cause before digging into the dash. Looks like I may have a better idea as to the cause...its probably the switch.
Le Mans Master
Joined: Aug 2000
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From: Australia
The relay in it's static (off ) state connects to the resistor bank and when powered up bypasses the resistors
and puts batt power direct to the fan motor for Hi speed.
If as you say the relay is working correctly ( not locked in the on position ) then it can only be in the on position
because the blower switch is also locked on Hi and not moving to supply power to the resistor bank for the other speeds.
