HVAC (heater AC) wiring diagrams please?

Tiny
MPYROL
  • MEMBER
  • 2 POSTS
Thank you. It seems like they would have produced a schematic showing two plugs. The 96 -99 units had a single harness I was not sure if what I had was correct but it is the same as these. Turns out there were 2 bad PNP transistors on the control board.(4 total) 4687 and 2857 were replaced with 2n4403. The other two that are close to the potentiometers are NPN 2857 and can be replaced with 2n4401. Works great now. Thanks
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,014 POSTS
Hi,

Excellent job. Interestingly, schematics never seem to make sense. LOL Regardless, I'm glad it's fixed.

Take care and let us know if you have questions in the future. You are always welcome here.

Joe
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
DANIEL HOLLAND
  • MEMBER
  • 7 POSTS
  • 1994 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 277,000 MILES
I have replaced the A/C heat plug on back of the control unit and I have two orange wires and a thicker tan wire left to connect. Every time I connect the tan wire something starts clicking and my lights on unit flicker. Not sure what it is for but I have power to unit can hear heater kick in but no fan to blow air when all this worked before the plug quit.
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
It sounds like you have some wiring that is crossed or something.

Here is a wiring diagram (below) that will help you get the problem fixed:

Please let us know what happens.

Cheers, Ken
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
DANIEL HOLLAND
  • MEMBER
  • 7 POSTS
Because there is a different plug I need to know what color wires go to certain pins on the plug in case they are wired different. Any help would be great
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
DANIEL HOLLAND
  • MEMBER
  • 7 POSTS
The factory plug had a number 2 on it and all others I have seen for this year model is 3, 4, 5 so they have to wire up different I would think
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
Can you upload some pictures of what you are doing so I can see?
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
DANIEL HOLLAND
  • MEMBER
  • 7 POSTS
This clip or plug that was in the dash right above the ashtray area what's the problem for the short is the reason I was not getting power replaced connected heat air module and now the lights are flashing like it's in the default mode so I cannot tell if the AC works or not I disconnect the battery reconnect the battery and everything is fine till I push a button I research this and a lot of people say that it was low low pressure on the compressor so I buy refrigerant put refrigerant in and I'm still seeing no difference any help would be appreciated thank you
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
O man, that is burnt up which is caused by the blower motor or relay pulling to many amps, try connected the wiring directly and disconnected the blower motor to see if the system powers up.

Thanks for the pic, it really helps.
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
DANIEL HOLLAND
  • MEMBER
  • 7 POSTS
I checked the relays and all make the clicking noise and have resistance of 76 on them all have power I pulled the heat AC fuse while the truck was turned on and replaced it to reset the AC heat control module and it still doing the same thing I will pull the blower motor connector tomorrow and see if that has anything to do with it I can hear The blower motor kick in on high-speed but it seems like it's on very low I cannot test my AC because of the flashing but I can hear my compressor kick in and out every five seconds
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
Disconnect the compressor as well to see if the system starts working.
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
DANIEL HOLLAND
  • MEMBER
  • 7 POSTS
Ok I unplugged ac and blower motor and still same thing. The blinking it can't be the control unit cause I have 2 of them and they both blink not sure what the deal is this on is gonna be for the vintage Record books once we figure this out
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Friday, April 30th, 2021 AT 12:37 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
Yep this is a good one for sure lol. Can you check the black wire to the controller to make sure it is grounded?
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Friday, April 30th, 2021 AT 12:37 PM (Merged)

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