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so i know i have several options, but what has everyone done? i plan to have a boost cam and it'll be turbo'd. on lt1swap.com it says the pcm will adjust idle as necessary with load, but to what extent? i can run the factory foxbody controls and completely ditch the pcm wiring/functions controlling a/c, or keep the pcm control and just send the 12v request signal via the factory switch.
what has everyone done? any step by step instructions? im re-doing my own harness and wondering if i should just remove the a/c pins? ill prolly get a sanden compressor since i dont have one, and get new factory fox evaporator/etc. will this work?
im more so concerned about the wiring/electrical aspect and idle under load
ECU adapts for loads, so idle is unaffected. Just use the trinary switch. One side to trigger high and low for compressor (wired in series) and the other triggers fan control relay. I have one large Fan. It is run by two relays mounted in parallel. One is from the trinity switch. The other is from the ECU (or PCM).
good luck.
Just make sure you use a fixed displacement compressor. Easier that way.
Agreed on the trinary switch for fans. Works amazingly well.
Originally Posted by DW SD
ECU adapts for loads, so idle is unaffected. Just use the trinary switch. One side to trigger high and low for compressor (wired in series) and the other triggers fan control relay. I have one large Fan. It is run by two relays mounted in parallel. One is from the trinity switch. The other is from the ECU (or PCM).
good luck.
Just make sure you use a fixed displacement compressor. Easier that way.
Where did that diagram come from?
I'm running 2 fans. One is actuated by the ecu (relay ground) with the lower setpoint.
The other fan is grounded by the ecu (higher setpoint) and/or the fan control of the trinary switch.
The compressor is powered by 12V directly through the trinary switch.
Where did that diagram come from?
I'm running 2 fans. One is actuated by the ecu (relay ground) with the lower setpoint.
The other fan is grounded by the ecu (higher setpoint) and/or the fan control of the trinary switch.
The compressor is powered by 12V directly through the trinary switch.
I actually have two fan control relays (for the same fan) in parallel feeding 12V+ power to the fan. Both could be on at the same time, but I see no harm in that. (one triggered by ground through trinary; the second triggered through ground from the PCM)
The reason is....
I was told you shouldn't back feed ground in to the PCM, which the trinary switch will do in your setup. The way it is wired in the second sketch, you'd need a diode between the PCM and the trinary switch relay to isolate.
In my case, both 12V+ tie to the input on the fan. There is no harm in backfeeding 12V to a relay.
Never heard about the backfeed issue. Been running that way for years.
What issues come up with backfeeding a ground?
Originally Posted by DW SD
I actually have two fan control relays (for the same fan) in parallel feeding 12V+ power to the fan. Both could be on at the same time, but I see no harm in that. (one triggered by ground through trinary; the second triggered through ground from the PCM)
The reason is....
I was told you shouldn't back feed ground in to the PCM, which the trinary switch will do in your setup. The way it is wired in the second sketch, you'd need a diode between the PCM and the trinary switch relay to isolate.
In my case, both 12V+ tie to the input on the fan. There is no harm in backfeeding 12V to a relay.
Never heard about the backfeed issue. Been running that way for years.
What issues come up with backfeeding a ground?
i can personally see no issues with backfeeding a ground whatsoever in this situation, but open to reasons why it would be. the only issue i can see is if u were not using an internal diode relay and having power on pin 85 from across the coil when not grounded and then backfeeding a 12v signal to the ground pin of the pcm. that would cause problems.
I see exactly what you are saying but whats the reasoning for not back feeding? Prolly not ideal, but will it hurt anything?
Originally Posted by garys 68
Never heard about the backfeed issue. Been running that way for years.
What issues come up with backfeeding a ground?
If you back feed the ground to the PCM, it will set a fan relay control code, but it won't hurt anything. I'm not sure if that code will trigger the MIL since I don't have one. But I've been running my car that way for years and with 81k on the odometer, most of which is in the summer when the A/C is needed, I have never had an issue with it. If it does trigger the MIL, it's possible you could just turn off the error reporting with some tuning software I would think.
It may be a code that doesn't set the light off, and then resets after the problem goes away, like turning the air off. Have you scanned it right after driving it with the A/C on? I've cleared mine and drove the car with the air off and it's fine, turn the air on and it sets the code. Doesn't cause any problems though.
Never bothered to scan....If I cant see it, it's not a problem
Originally Posted by ls1nova71
It may be a code that doesn't set the light off, and then resets after the problem goes away, like turning the air off. Have you scanned it right after driving it with the A/C on? I've cleared mine and drove the car with the air off and it's fine, turn the air on and it sets the code. Doesn't cause any problems though.
The comments here reminded me... on my Gen IV system, I did trigger a CEL when I wired both trinary and PCM triggers to the one relay. That is why I ended up wiring the two relays. Not much more complicated to do it with a second relay and an isolated stud to fee the cooling fan.
Sounds like either should functionally work.
I believe the computer runs diagnostics on a regular interval to check resistance on the line. When it "sees" other circuitry, the resistance will be different than expected and it triggers the CEL.
I don't think it will break the computer. It did not mine
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a/c options. not sure what to do? 
