microprocessor in dash for ac?
Elder User
Joined: Nov 2014
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From: Charles Town, WV
The ecm has the final say if the compressor runs or not. What problem are you having?
It is possible to take the ecm out of the equation fyi. I had to do it with my cummins swap because even though I was sending the ecm a tach signal, it was being bitchy and wouldn't run the compressor (guess it wants more input than just the tach)
It is possible to take the ecm out of the equation fyi. I had to do it with my cummins swap because even though I was sending the ecm a tach signal, it was being bitchy and wouldn't run the compressor (guess it wants more input than just the tach)
Elder User
Joined: Nov 2014
Posts: 582
Likes: 7
From: Charles Town, WV
The electrical side of it is
Function selector switch -> A/C compressor cycling switch -> A/C high pressure switch -> PCM -> K107 A/C clutch relay -> A/C clutch -> A/C compressor clutch diode.
Function selector switch -> A/C compressor cycling switch -> A/C high pressure switch -> PCM -> K107 A/C clutch relay -> A/C clutch -> A/C compressor clutch diode.
Hotshot
Joined: Jan 2004
Posts: 19,763
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From: St Louis
The compressor is controlled differently depending on the year, the engine, and the climate control system installed. NONE of those have been identified.
If a "mechanic" has replaced three compressors and it still doesn't work, he doesn't know what he's doing except to guess.
If a "mechanic" has replaced three compressors and it still doesn't work, he doesn't know what he's doing except to guess.
Elder User
Joined: Nov 2014
Posts: 582
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From: Charles Town, WV
Durr, forgot about some having the digital climate control. I was thinking about the standard style with the *****.
But agreed, swapping out 3 compressors and still having the same issue is just a guy throwing parts at it hoping to fix it.
But agreed, swapping out 3 compressors and still having the same issue is just a guy throwing parts at it hoping to fix it.
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Hotshot
Joined: Jan 2004
Posts: 19,763
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From: St Louis
Durr, forgot about some having the digital climate control. I was thinking about the standard style with the *****.
New User
Joined: Feb 2020
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The ecm has the final say if the compressor runs or not. What problem are you having?
It is possible to take the ecm out of the equation fyi. I had to do it with my cummins swap because even though I was sending the ecm a tach signal, it was being bitchy and wouldn't run the compressor (guess it wants more input than just the tach)
It is possible to take the ecm out of the equation fyi. I had to do it with my cummins swap because even though I was sending the ecm a tach signal, it was being bitchy and wouldn't run the compressor (guess it wants more input than just the tach)
Elder User
Joined: Nov 2014
Posts: 582
Likes: 7
From: Charles Town, WV
This way
Originally Posted by Gots_a_sol
Boring reading ahead, just ignore if you don't plan on ever putting a cummins in an Ex or Super duty :lol:
So the a/c works through the computer. And apparently the computer is fussy about what inputs it gets before it will send a signal to the a/c clutch relay. Solution is to bypass it with another relay.
This info is for a 2000 Ex with a v10. Other years/engine types may vary.
The original relay is in the power distribution box #302. Pin 86 is grounded by the computer to activate the a/c clutch.
To make it work, you pick up the wire coming from the high pressure switch to the computer. It is Tan/Lt. Green and goes to pin 41 at the pcm. You can either grab it at the switch or at the pcm, I chose the pcm since you're working in that area anyway. This wire has +12 volts on it when you select a/c and when the high/low pressure switches are in their correct positions. You will connect this wire to pin 85 on the new relay.
The wire that goes to pin 86 on the original relay is Pink/Yellow (may be red/yellow). I don't know what pin it is at the pcm, I just picked it up in the fuse box. You will connect this wire to pin 87 on the new relay.
Pins 30 and 86 are grounded on the new relay.
The idea is that when you turn on the a/c, you end up with +12 volts going to the pcm (now new relay). You need ground to trigger the a/c clutch relay, so the new relay is just flipping the 12 volt signal to a ground signal.
Recap:
Tan/Lt. Green = pin 85
Pink/Yellow = pin 87
Pins 30 and 86 are grounded.
Boring reading ahead, just ignore if you don't plan on ever putting a cummins in an Ex or Super duty :lol:
So the a/c works through the computer. And apparently the computer is fussy about what inputs it gets before it will send a signal to the a/c clutch relay. Solution is to bypass it with another relay.
This info is for a 2000 Ex with a v10. Other years/engine types may vary.
The original relay is in the power distribution box #302. Pin 86 is grounded by the computer to activate the a/c clutch.
To make it work, you pick up the wire coming from the high pressure switch to the computer. It is Tan/Lt. Green and goes to pin 41 at the pcm. You can either grab it at the switch or at the pcm, I chose the pcm since you're working in that area anyway. This wire has +12 volts on it when you select a/c and when the high/low pressure switches are in their correct positions. You will connect this wire to pin 85 on the new relay.
The wire that goes to pin 86 on the original relay is Pink/Yellow (may be red/yellow). I don't know what pin it is at the pcm, I just picked it up in the fuse box. You will connect this wire to pin 87 on the new relay.
Pins 30 and 86 are grounded on the new relay.
The idea is that when you turn on the a/c, you end up with +12 volts going to the pcm (now new relay). You need ground to trigger the a/c clutch relay, so the new relay is just flipping the 12 volt signal to a ground signal.
Recap:
Tan/Lt. Green = pin 85
Pink/Yellow = pin 87
Pins 30 and 86 are grounded.
New User
Joined: Feb 2020
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I *think* I found a wiring diagram from an '00 Excursion to compare with, Correct me if I'm wrong, but on your truck, your A/C selector panel wires directly into the High Pressure/Cycling switch circuit. On my '05, it appears the A/C selector panel sends it's signal as a request to the PCM, so I would have to find a way to bypass the PCM from there as well. Does that sound right, or am I overthinking this?
Elder User
Joined: Nov 2014
Posts: 582
Likes: 7
From: Charles Town, WV
I missed you were asking about something other than an Ex. Skimming around the diagram it looks like your signal goes from the EMTC to the instrument cluster then to the PCM via CANbus signal. Not great news there for trying to work a bypass easily.
You could add a switch to manually run the compressor but I'm not sure how that is going to play with the computers. Basically the same idea as what I did on my Ex.
Blk/Yel at the pcm is your +12v from the safeties, run this to pin 85 on a new relay
Pnk/Yel at the pcm is your ground signal for the A/C clutch relay. Route this wire from the a/c clutch relay to pin 87 on the new relay
Ground pin 30 on the new relay
Ground pin 86 on the new relay via a toggle switch
You could add a switch to manually run the compressor but I'm not sure how that is going to play with the computers. Basically the same idea as what I did on my Ex.
Blk/Yel at the pcm is your +12v from the safeties, run this to pin 85 on a new relay
Pnk/Yel at the pcm is your ground signal for the A/C clutch relay. Route this wire from the a/c clutch relay to pin 87 on the new relay
Ground pin 30 on the new relay
Ground pin 86 on the new relay via a toggle switch
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