diagram request

Greg5OH

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Does someone have a pinout diagram for the HVAC on a 91 truck? need it for the function switch and blower switch pretty please.
part stores dont have this stuff.
 

Clb

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93 is a new dash ? Right?
I have an 88 and 93 fsm.
 

3Kp

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Not sure if this is what your looking for? I have a blown up wiring diagram for whole wire system if that's what your after.

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Let me know if it attachment doesn't work. Me and this computer are about to go around and round!
 

Clb

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I can't see it' BUT I am on an ifail phone.
 

3Kp

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Try again!

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I'll try this again if it doesn't work PM me tomorrow with your email or cell phone and I'll send it over to you.
 

Greg5OH

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Yes thay works thanks!!
2 questions- the terminal locations pinout, thays looking at the backnof the blower speed switch ya?
2) do you have the pinout forbthe heater function selector awitch(similar to the blower pinoit olyou showed?
 

3Kp

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I'll dig thru the book tonight when I get home.
 

3Kp

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Blower switch terminal and schematic

Greg this is all they have in the book. I took a better picture of the terminal and schematic .

ZWillson07 have a set of manuals for sell. This is where I'm getting you the info from. Search in marketplace 1990 Factory Repair Manuals (Great Shape)

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Greg5OH

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ok thanks. I swapped my wiring around to reflect that, still no change. No voltage at the blower. Dunno boys..?
Anyone know the wiring order for the function selectro switch?
Pretty much lost on this one. Gave my cables some slack though, dash is going back on tomorrow. Just going to do a continuity check on all my home made wires to make sure its not a broken connection somewhere.
 

LCAM-01XA

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OK, remember the speed selector switch is on the ground side of the motor, you won't see any voltages on any of its pins if there's no voltage getting to the motor first. The motor voltage supply is controlled by the function selector switch, on that one you should only have four wires:
- two brown/white ones, those get key-on power via a 30-amp fuse (#9 in the factory panel)
- a single brown/orange wire that feeds voltage to the blower motor at all times except when slide lever is at its left-most "off" position,
- a single lightgreen/pink wire that feeds voltage to the A/C compressor clutch via the pressure switch on the accumulator/dryer.

So basically with the ignition on if you're getting voltage at the brown/white wires but not on the brown/orange one that means your switch is bad. If no voltage at the brown/white wires at all that means your problem is somewhere upstream from the switch, like a blown fuse or a wire not connected to the right place in your aftermarket fuse panel.
 

Greg5OH

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thanks LCAM. yes I am getting voltage at both brown/white wires. I am wondering if maybe i hooked them up wrong though? Looking at the back of the Hvac unit i have
purple, br/w, br/orng, br/w
is that the correct order? If so then that leaves the blower speed switch as bad?

PS I am looking at new switches, btu that the heck is this black connector?? I dont have this on mine?
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LCAM-01XA

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That is the correct order indeed according to the EVTM. Test the switch by jumping the wires, take a paper clip and straighten it and touch the connector contacts from the back, go between the br/o wire and any of the the br/w wires. Make sure your blower speed selector switch is plugged in and set to high, this will bypass the resistor pack and give you the simplest circuit possible (good for diagnostics purposes). If blower comes alive then your function selector switch is dead.

What black connector?
 

3Kp

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The black connector is for a AC. In my 87 F150 it has a push button for the AC instead of the slide selectors like in my 91
 

LCAM-01XA

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Ah yes I see it now. Yes the '87 and early '88 trucks have the A/C compressor on a stand-alone switch. Also, the linkage between the selector levers and the respective air doors is all mechanical on those trucks, just cables and levers, no vacuum servos (well maybe except for the recirculating door, that could be vacuum-powered). Meaning if you got one w/o factory cruise, and you hydroboosted it, you could effectively delete the vacuum pump from the engine altogether (recirculating door defaults to fresh air with no vacuum, it only closes in the max-A/C and off positions).
 

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