Are these Fan relay connection correct?
Are the connection numbers on the relays correct?
Originally Posted by Jones'n
Not sure what you are asking, but yes, that diagram is correct for the factory fan wiring.
Sorry for making myself clear.
I see two things. Yes you switched 87 and 87a on relay 3. 30 will be connected to 87a when de-energized and 87 when energized. A typical schematic always shows the relay in the de-energized state so you need to switch 87 and 87a on 3. Also on 1 and 2 you have 85 as + and 86 as -, but on 3 you have it the other way. It should work just fine as long as there are no diodes internal to the relay.
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Originally Posted by 70 LS1
I see two things. Yes you switched 87 and 87a on relay 3. 30 will be connected to 87a when de-energized and 87 when energized. A typical schematic always shows the relay in the de-energized state so you need to switch 87 and 87a on 3. Also on 1 and 2 you have 85 as + and 86 as -, but on 3 you have it the other way. It should work just fine as long as there are no diodes internal to the relay.
Last edited by Tri5Nerd; Aug 14, 2006 at 06:56 PM.
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Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Your a couple days ahead of me, I was going to post this tomorrow, but it looks like you could use it now 
This is the way that GM hooks up the cooling fans for high and low speed. When the fans are on the low setting they are wired in series and each receive 6 volts, when the high speed relay kicks on the fans are wired in parallel and receive 12 volts. This hookup will work for all 98-02 f-body PCM`s, the relay terminal numbers are based on the standard bosch automotive style relays.
Relay # 1
terminal
86 to C100 pin J
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 1 cooling fan
Relay # 2
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 2 cooling fan
Relay # 3
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to - side of # 1 cooling fan
87 to ground
87A to + side of # 2 cooling fan
the - side of cooling fan #2 goes directly to ground.
This is the way that GM hooks up the cooling fans for high and low speed. When the fans are on the low setting they are wired in series and each receive 6 volts, when the high speed relay kicks on the fans are wired in parallel and receive 12 volts. This hookup will work for all 98-02 f-body PCM`s, the relay terminal numbers are based on the standard bosch automotive style relays.
Relay # 1
terminal
86 to C100 pin J
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 1 cooling fan
Relay # 2
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 2 cooling fan
Relay # 3
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to - side of # 1 cooling fan
87 to ground
87A to + side of # 2 cooling fan
the - side of cooling fan #2 goes directly to ground.
Originally Posted by G-Body
Your a couple days ahead of me, I was going to post this tomorrow, but it looks like you could use it now
This is the way that GM hooks up the cooling fans for high and low speed. When the fans are on the low setting they are wired in series and each receive 6 volts, when the high speed relay kicks on the fans are wired in parallel and receive 12 volts. This hookup will work for all 98-02 f-body PCM`s, the relay terminal numbers are based on the standard bosch automotive style relays.
Relay # 1
terminal
86 to C100 pin J
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 1 cooling fan
Relay # 2
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 2 cooling fan
Relay # 3
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to - side of # 1 cooling fan
87 to ground
87A to + side of # 2 cooling fan
the - side of cooling fan #2 goes directly to ground.
This is the way that GM hooks up the cooling fans for high and low speed. When the fans are on the low setting they are wired in series and each receive 6 volts, when the high speed relay kicks on the fans are wired in parallel and receive 12 volts. This hookup will work for all 98-02 f-body PCM`s, the relay terminal numbers are based on the standard bosch automotive style relays.
Relay # 1
terminal
86 to C100 pin J
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 1 cooling fan
Relay # 2
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + side of # 2 cooling fan
Relay # 3
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to - side of # 1 cooling fan
87 to ground
87A to + side of # 2 cooling fan
the - side of cooling fan #2 goes directly to ground.
This info should be added to the sticky for future reference.
non factory fan Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Originally Posted by lechner80
Can anyone show me how to wire up a 2 speed fan (3wires) with relays and the pcm control for high and low speed. Thanks John L
terminal
86 to C100 pin J
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + low speed wire on fan
Relay # 2 High speed relay
86 to C100 pin H
85 to + IGN source (old HEI power wire)
30 to cooling fan fuse (size depends on amperage of fans) then directly to constant battery power
87 to + high speed wire on fan
Then ground the ground wire on the fan and your done.
I am running and earlier f-body a/c compressor. How would I tie it in to this wiring to make the fan comeon with the compressor. My compressor is not hooked to the pcm anywhere.
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Originally Posted by LS1MCSS
I am running and earlier f-body a/c compressor. How would I tie it in to this wiring to make the fan comeon with the compressor. My compressor is not hooked to the pcm anywhere.
I was just reading in the service manual about this. The PCM turns on the fans based on refrigerant pressure, not the A/C request signal.
When the PCM gets the A/C request signal from the HVAC module it (PCM) then turns on the A/C compressor. Once the PCM senses refrigerant pressure going up, it turns on the fans.
I think you are going to have to supply a signal directly to your fan relays when the A/C turns on. I'm not real familiar with A/C, but there should be some place on the compressor that goes hot when the A/C turns on. You can tap off of that and send it through a relay to supply a ground for your fan relays.
When the PCM gets the A/C request signal from the HVAC module it (PCM) then turns on the A/C compressor. Once the PCM senses refrigerant pressure going up, it turns on the fans.
I think you are going to have to supply a signal directly to your fan relays when the A/C turns on. I'm not real familiar with A/C, but there should be some place on the compressor that goes hot when the A/C turns on. You can tap off of that and send it through a relay to supply a ground for your fan relays.
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Well I guess I am not triggering my fans via the PCM, I was hoping the fans got the trigger signal when the A/C request was given but I guess I`m out of luck there. I`ll think about how to do it today, but I think triggering the fans directly will require either a relay and 2 diodes or 2 relays. Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Originally Posted by LS1MCSS
I am running and earlier f-body a/c compressor. How would I tie it in to this wiring to make the fan comeon with the compressor. My compressor is not hooked to the pcm anywhere.
Relay #1
85 to the A/C request wire from your car (the wire that provides power to the cycling switch on the A/C accumulator)
86 to ground
30 to ground
87 tapped into the wire from the computer that controls the low speed cooling fans (C100 pin J)
Relay #2
85 to the A/C request wire from your car (the wire that provides power to the cycling switch on the A/C accumulator)
86 to ground
30 to ground
87 tapped into the wire from the computer that controls the high speed cooling fans (C100 pin H)
These 2 relays are in addition to the 3 relays that you will need to control the high and low speed fans.
I think that you might be able to use 1 relay instead of 2 and then use 2 diodes to isolate C100 pin J and C100 pin H and then put the output of the single relay between the diodes. But I am not positive that that will work and have not tested it yet so I don`t recommend trying it. Of course after reading the above statement I just realized that I probably confused everyone who read it
unless they are electrical engineers in which case they would probably know if that would work. 