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93 vr4: a/c functional but wont kick on, tried many thing

4K views 18 replies 9 participants last post by  stealthtuner83 
#1 ·
see this post for what ive tried and the backstory:
http://www.3si.org/forum/f1/c-control-unit-computer-location-part-659186/index4.html

I just bought this car:

http://www.3si.org/forum/f10/93-vr4-...des-8k-648593/

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this is off a 1993 mitsubishi 3000gt vr-4
the car has a digital touchscreen climate control system.

the compressor was tested and fine. mitsu said it was a short or more like the a/c computer. a mechanic searched for a short and said he thinks its the a/c control unit.

i went on to replace this and it didnt change anything.
ok so i switched out the a/c control module/unit (brainbox for the dcc): Digital Climate Control Computers | 3S Warehouse

it didnt fix it. maybe its just in my head but the air coming out seemed cooler, but not cold. i dont think the compressor is kicking on at all. i dont know where its located in that messed of components i can barely see and i dont hear it (to my knowledge) click on and engage.

short version:

took the car to mitsubishi. they did r12-r134 conversion, did an evac and fill, tested for leaks and tested compressor. wouldnt engage from the dcc. they put voltage into the relay and it would work perfectly. the signal just isnt getting to the compressor.

they said ecm. which im not too familiar with but i dont see how that could be. i hear this controls all components in the car, not just a/c. now granted, the car was a project, it was built from the ground up, started as a shell and the engine, tranny and most components were new. i cant say the cruise control, active aero, tunable exhaust, or sport suspension work. but cruise control makes a light come up on the dash when i press the switch, asc on, but there is no switch on the steering wheel.

im just trying to give a general idea about the car. i think what he meant was the a/c control unit/module, ecu, comuter, brainbox, whatever you want to call it. i mean this directly controls the a/c.

when i press on the button on the dcc, the symbol comes up, everything works properly from the dcc, except the a/c doesnt actually come on when the symbol is there.

we know the compressor is good
there are no leaks
dcc appears to work fine
a/c control unit (brain box) was replaced (used unit, but from decent shop)
compressor engages when given voltage to the relay

so i am going to try this next.
it fits the symptoms, its cheap, and idk what else to do:

AC Compressor Lock Module | 3S Warehouse

this tells the clutch to engage the a/c.

i replaced this....
there was no ac compressor lock module. it was just the wiring harness dangling there.



so the harness was just dandling there. the plastic piece it sets in thats under the GC is not there at all.

obviously this should be the issue with the ac.

i just tried to test it and couldnt tell that it was working. to me it seems like it wasnt.

but that was with everything shown removed. so there air was barely going out of the vents at all. it was mostly blowing around by the glove boc. but it didnt feel cool or cold to me. maybe barely cool.
i know a mechanic would check everything from a flow chart. but i cant afford hundreds on diagnostics, and cant do it myself.

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then a ac repair man come over to work on our home ac. he said he used to have a 3000gt so he seemed like the perfect person to look. he told my dad hes take a quick look for free. he check the voltage and wiring under the glove compartment and the new clutch controller i put in. he said everything was functioning properly. all parts of the ac were doing what they should but the air is just not cold.

fans engage, light for ac is on in the dcc. at mitsubishi 2 months ago when they filled the frion they said it worked fine manually turned on when given voltage from the relay. that the ac works fine it just isnt getting the signal to kick on. and that they problem was not after the relay but before it .

so then this new ac repair guy seemd to say the opposite. he checked the relays in fuses in the box. 2 were removed (i think for the fans) bc the car has aftermarket cooling fans and radiator. so the relay may have been bypassed or connected differently. they kick on and off automaticallt just fine.

anyways the ac repair guy said the problem is from the relay to the ac compressor. i tried to confirm and he said yes i believe but this doesnt make sense to me.

if there is a problem from the relay to the compressor then how come mitsubishi can send voltage to the relay to the ac compressor to kick on and blow cold air? but it wont do it automatically.

this seems to make it sound like form the relay to the dcc there is a problem .

what do you guys think. im running out of ideas. i checked the relay, changed some fuses, and tightened it down and checked the ground. outside of that idk what to do with a mess or wires taped together and wrapped up.

please help.
 
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#2 ·
bump it.
 
#4 ·
that is some very good information. it sounds like something like this could keep it from working.

but... how do i diganose that this is the problem? i dont have a part number. a how to remove and install could help bc then i could get the mitsu name. photo sensor maybe.

input?
 
#5 ·
photo sensor:
but... how do i diganose that this is the problem? i dont have a part number. a how to remove and install could help bc then i could get the mitsu name. photo sensor maybe. pics?
 
#7 ·
pressure switch? does it go by another name? bc i have heard about it on 3si yet, through the service manual or from the mechanics. location? function?

photo sensor: can anyone show me a pic or a illustration with a location from a manual? does anyone think this could likely be it ?
 
#9 ·
What are the high and low side pressure readings?

If there is no pressure, there is a leak. If there is low pressure, there is a leak.

On my 1998, I jumped the A/C relay and while sucking in r134 to get the compressor going. Once pressure increased, the compressor worked without needing to be jumped.
 
#10 ·
the car has been to mitsubishi already, they dyed it, did a leak test and got the system running through the relay no leaks whatsoever. it just doesnt kick on by itself.
 
#11 ·
bump!!
 
#14 ·
I had similar a/c issues to those described above and tried several different things with no help including a trip to the dealership. Finally I worked through the troubleshooting list posted on stealth316.com and it turned out to be a bad relay, which took all of 30 seconds to swap out and fix. Diagrams and instructions for testing the relays are on the site.

Regarding the other questions, I believe the cars come with either a sensor or plastic cap, not both, so no, you do not need a cap over your sensor.
 
#16 ·
where is the revolution sensor. Diagram/photo?

does anything think its the photo sensor? diagram/photo?

i replaced one of the relays for the ac. didnt do anything. could be another one buti did check them out to the best of my abilities.

i suck at wiring and wiring diagrams. i think it would be a good idea. i replaced the module that makes the ac clutch kick on. nothing. hard to say what it is. but i had an AC service person (for our home ac) look at it, who had a 3000gt. he said everything was operating properly. we had the glove box etc out and he could see and hear what was kicking out. said the compressor didnt engage and the air wasnt cold but everything else was fine.

again you can manually engage the ac and it works fine but thats with voltage thru the relay.
 
#18 ·
yea that might be a good troubleshooter. alot of steps but i could try.

any thoughts on the problem?
 
#19 ·
bump..
 
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