Resolved 2G - A/C Control Unit ECU

[MarkAngelo05]

Hi..

My a/c was just working, I do not know why it stopped. Here are the symptoms,

-A/C turned on, idle raises, but compressor does not come on. The passenger side fan blips on and off the whole time, until I reach 210 then it comes on to cool the car down.
The drivers side fan never comes on now.

I tried to fill the a/c system up, but the LOW side port was just way too pressurized, so it would not let me insert any more freon, it pretty much kept most of the freon in the can.

I tried emptying the system to lower pressure, then used a new can of freon, slowly let it pressurize the system, but the a/c compressor does not kick in, nor the drivers side fan. I made sure the green A/C Light was on the whole time.

What could be the problem??? IT used to work, now I'm stuck!

Thanks!

Mark

IS the Driver's side fan supposed to come on even if the compressor clutch doesn't kick in while the GREEN LIGHT A/C Indicator is on??

Also, I'd really like to know if anybody else has experienced the passenger side fan blipping on and off.. fast small blips of power, and it moves slowly.. until the engine gets to around normal 210 degrees then it turns on.

Thanks!

Mark

------I "JUMPED" The a/c compressor clutch and got the compressor to 'kick in' BUT, the Drivers side fan still does not come on... My passenger side fan comes on when it reaches the appropriate temp to kick on....


What could be the problem??? IT used to work, now I'm stuck! Can it be the ECU? Doesn't the ECU control both fans and also controls the drivers side fan when the A/C is button is turned on and the green light is on? It also controls the a/c compressor clutch, correct???

Hi, I'm trying to diagnose my ac problem. Someone please tell me where the lowside a/c pressure switch is located. I cannot find any info in this stupid Chilton's manual.!

Thanks!

Mark Padilla

 

[luv2rallye]

The A/C light indicator comes on just when the A/C button is pressed and the blower is in any not off position and ignition switch is on - nothing else. If you still have the 2 speed factory fans and wiring, the ECU controls the passenger side hi and lo speeds and the driver's side hi. The driver's side lo fan is controlled by the automatic compressor control module which uses a FIN thermo sensor inside the car. To turn on the A/C compressor, the automatic compressor control module, dual pressure switch, A/C refrigerant temp switch, and part of the ECU must all be activated.

 

[luv2rallye]

If you mean the dual pressure switch, it's just rear of the LF headlight low beam.

 

[mitsured420]

Are you using ac guages?jump the compressor check your pressures,depending on ambient temp should be about 30-40psi low side,150-200 high side.you could be low on freon you compressor wont cycle if its low.Driver side fan cycles with comp. check relays and fuses also.

 

[MarkAngelo05]

Hi, I appreciate your replies!

I switched ECU's back to my 97 ECU, still the same problems, so its not the relays in the ECU,

I'm around 40 psi on the lowside when I "jump" the compressor, I don't have a gauge for the high side.. but as I rev the car higher, it drops lower and lower in pressure, but then raises back up to 40. THE AIR GETS PRETTY COLD TOO!! but while I'm doing that, the fans don't come on and the HOT/HIGH SIDE GETS REAL HOT!! So I had to jump the condensor low speed fan relay to turn both my drivers side and passenger side fans on during the process.

I'm thinking it may be a stuck switch?

The pressure switch at the dryer and is by the headlight is the HIGH side Pressure switch correct??

Doesn't this car have some kind of other pressure switch/cut off switch? this sux ### it gets pretty hot here...

Mark

 

[Defiant]

The AC has its own control unit on the evaporator. I don't know how to test it, but put it on the suspect list.

 

[MarkAngelo05]

Hi there, thanks defiant! I read that on the "mitchell repair information company" repair CD at the Auto hobby shop on base. However it did not tell me where the ACCU Is located... the A/C Control unit on the 2G's only has 3 leads to it Power supply output, power supply input and ground.. BUT I CANNOT LOCATE IT.. if anyone here can please tell me where it is on a 2G, that'd be great. It says it's by the BLOWER MOTOR., but I cannot see it. Isn't the blower motor right next to the evaporator???To the right of it right???

Thanks!!!


Mark

 

[luv2rallye]

Yes the blower motor is to the right of the evaporator (behind the glove box door). The ACCU is a plastic box attached to the front of the evaporator with a small connector on the top. The green/orange wire should go to +12V (which then goes to the dual pressure switch, A/C refrig temp switch, compressor clutch relay, and ECU) when it wants to turn on the A/C compressor.

 

[MarkAngelo05]

Alright, I saw that switch, it's only 3 wires on the connector, then it's got yellow wires coming out of the back of it, into the evaporator housing.. I assume that's the fin thermo sensor. How does it give info and receive info from all the other sensors?? hmm.. anyways, I'm just gonna put a voltmeter to it! If that's the problem, what is the other side connected to? ANYONE GOT A PART NUMBER FOR THAT!???!!

thanks!

Mark

 

[luv2rallye]

Yes the 2 wires out the back go to the FIN thermo sensor inside the evaporator. If you get +12V on the green/orange (ACCU power output) when you turn on the A/C and blower, then the ACCU is working. That 12V then goes in series first to the dual pressure switch (also to the drivers side fan relay lo) and from there to the A/C refrig temp switch so you can see if you have +12V after each of these to see if they are working. If so then either the A/C compressor relay is bad or the ECU is not turning that relay on (by providing ground). Note the ECU also requires the engine coolant temp sensor to be working.

If the green/orange does not have +12V when it's supposed to, make sure there is +12V on the blue/black (should be since your A/C light went on). If so, make sure the black wire connects to ground and then measure the resistance of the FIN thermo sensor (should be around 5k ohms at 68F). If ok the ACCU is bad.

 

[MarkAngelo05]

Hey Luv2rally, (wish i knew your name) ,

well, thanks for even more information! I have tested my relays and all of them are in working condition. When I pull out the FAR RIGHT Relay, I think is Condensor fan relay, and push the A/C Switch ON, the passengerside fan comes on, and If I pull the pressure switch , the fan turns off, and also when I pull the temp switch on the compressor itself, the fan turns off.. OR IF I PLUG THE FAR RIGHT RELAY(condensor fan relay) back in, the fan just stops working... so if that accu activates the compressor relay, what else does it activate?? the condensor fan aswell?? because my condensor fan does not come on unless I trip the relay itself...

Thanks for the info, I will be checking the accu SOON!!

mark

 

[luv2rallye]

Well when the +12V goes thru the A/C refrig temp switch, it goes to the ECU as well as the compressor relay. So the ECU knows that the A/C should be running and it then controls the passemger side fan accordingly. The fact that that fan stops when you pull the pressure or temp switches prove it. It sounds like your ACCU is ok then.

Do you still have the stock fans and wiring? If so, it sounds more like either the drivers side (condenser) fan lo winding is bad, or the condenser fan relay lo is bad, or there's bad wiring in these areas. With AC on, see if you have +12V on the condenser fan connector pin 1 (blue wire). If you pm me an email address that accepts attachments, I'll send you the wiring diagram.

Gary

 

[MarkAngelo05]

YOU'RE EXTREMELY HELPFUL! , you need another STAR!
Thanks for all the help bro! Well, I think it may be the wiring aswell. WHen I unplugged the accu, while the a/c switch was on, and the FAR RIGHT RELAY UNPLUGGED, the passenger side fan would not work, but after I plugged the accu back in, it started right up! so where does this ACCU Positive 12+ output go to? because I know if I connect the Compressor RELAY
-- --
| | <--------- the bottom right part of the pin

directly straight to the POSITIVE BATTERY LEAD, WHILE ALL THE RELAYS ARE IN, BOTH FANS TURN ON AND THE COMPRESSOR KICKS IN! BUT I go to turn off the a/c button inside, and nothin happens, they STAY ON!! It's mind boggling man.. all these wires and relays.. The diagram I got from that computer repair manual is worthless because its w/ the 12pin accu that comes in the non turbo models.

Okay, so what confuses me is that I thought the RELAYS WERE TRIGGERED BY A GROUND!!!?? Grounding the bottom left pin will trigger the relay for all the relays, but for the compressor relay, grounding the bottom left pin does not work.. When I connect ONLY THE bottom RIGHT pin to a 12+ source, is when it works (without grounding the bottom left pin). That is what got me confused.

So bottom line, the ACCU POSITIVE OUTPUT MUST TRIGGER which relays?? it seems like if it just triggered the Compressor relay, it would be good because just by manually doing so turns on all the a/c systems (both fans and compressor).

 

[luv2rallye]

YOU'RE EXTREMELY HELPFUL! , you need another STAR!)

I've never seen them give more stars to wisemen but you could try posting in the Reputation Recommendations forum (http://www.dsmtuners.com/forums/forumdisplay.php?f=101) to see what they will do - perhaps add to my reputation points - tee hee.

So bottom line, the ACCU POSITIVE OUTPUT MUST TRIGGER which relays?? it seems like if it just triggered the Compressor relay, it would be good because just by manually doing so turns on all the a/c systems (both fans and compressor).

It's more complicated since the ECU is involved which also controls the fans. I described where the output goes in posts 13 & 15 but you'll have to see for yourself so I'll email you the diagrams.

 

[MarkAngelo05]

Hi!

After various wire testing and diagnostics, I have finally found my culprit!!! It is a BLOWN ACCU. (A/C Control Unit), located on the evaporator housing! At first, it appeared not to be the problem because with the A/C condenser fan relay unplugged, it would deliver enough current to the ECU to raise the idle and turn on the Passenger side fan! But when I plugged that relay in, voltage would drop to 10.00 volts which was just not enough at all!

Its input was a good 12V, and the output was a mere 10.65 volts which was not enough to trigger the relays that are involved in the system. What I did to test my theory was jump the +12V input wire and the 12 volt output wire, which triggered my ECU and relays. BINGO! A/C Compressor kicked in, both fans turned on, and all was well. I'm heading over to my buddy's house to dismantle his evaporator housing so I can get the accu/fin thermo sensor because he does not have a complete a/c system!

Thanks so much for everyone's input, ESPECIALLY Gary's(luv2rally)!!!

here's a picture of the A/C Control Unit!!! It appears to have a blown transistor, circled in red!!!

You must be logged in to view this image or video.

Take care!

Mark Padilla

 

[luv2rallye]

You're welcome, glad to help and happy to hear you found the problem. Did the diagrams I sent you help with your final testing theory?
- Gary

 

[MarkAngelo05]

Hey Gary!

Yes, the diagrams you sent me sure did help! I wish I had printed out the correct ones at first, but THE ONES YOU SENT ME ARE VERY DETAILED... At first I thought that I fried one of the wires in the fuse/relay box, because they tested kind of awkward,but I traced it all down to the accu and retested, so pretty much anything less than 12v output from the accu is BAD!! or anything less than the INPUT voltage is BAD! I was just thinking of splicing the 12v input to the output wire, BUT I wouldn't want my evaporator core freezing to death.... It would still cycle on and off because the ECU has the final call on the whole a/c thing...
Thanks again!

Mark

 

[Defiant]

Yeh, that's swell. See Post #9.

 

[MarkAngelo05]

Thank you too Defiant! I had such a hard time looking for the a/c control unit at first because I just thought it would be a larger unit! kinda like a SMALLER ECU with a bunch of wires going to it, BECAUSE I HAD THE WRONG DIAGRAMS AT FIRST, but when I saw the 3 wire plug and 2 wires coming out of it, I was thinking maybe that was it, I saw a tab and popped it open and saw it was a circuit board...guess that's the most simple a/c control unit...

well, I ended up ripping the a/c control unit out of the donor car and the FIN THERMO SENSOR GOT STUCK ON THE EVAPORATOR... all I did was take the circuit board out and solder my sensor on the working one, so it's all good and my a/c is COLDER THAN ITS EVER BEEN!!!

Take care!

Mark Padilla

 

[roni-wan]

Hi!!

Bringing back the thread, i have similar problems with my a/c

when I turn it on the a/c fan(driver side) kicks in but compressor and passenger side fan doesn´t

Was thinking I also have a bad ACCU so took it off and seems fine but don´t know which wires are input and output

Hope someone could help

 

[RedTurboEclipse]

Wow this thread was very informative.

I will bring it back up because I have a situation. typing "a/c" in the search title only doesn't come up with anything, so I searched for "fan" and filtered the ones that had to do with the a/c.

This is the situation, we are trying to fix the AC on a 95 Eagle Talon TSi with 6-bolt swap. I don't know too much about our HVAC system, but all the a/c components seem to be in the engine bay. Lines, compressor, etc. We also just refilled it.

Now when I turn the a/c on via the switch inside the car, nothing happens. The light on the button does turn on. However I don't hear the compressor kick in or a/c fan turn on. (<-actually I forgot about the a/c fan turning on, never double checked). It is blowing normal air though because we turn up the fan setting to full blast, but don't know if thats th a/c fan or the other fan.

You know when you turn on the a/c, you hear the audible sound of the compressor and you feel the car's performance drop. In this case, car is like normal, no cold air.

I don't know where to start first. a/c shop who refilled the a/c said compressor is fine (don't know what kind of checks he did to verify that), fuses are fine, ac is refilled, don't know where to start.

 

[rkmillerjr]

95' GSX - A/C does not work. Dealership diagnosed that my A/C does not work because the A/C ECU (Control Unit) located behind the glove box needs replaced. Tried to order a new one. Mitsubishi Corp. does NOT have the part available anymore! They suggested that I check with salvage yards. I have, and none (I've checked with 8 so far) of them seem to have a clue of what part I'm talking about. Does anyone have any idea if this part really exist?? If so, any leads you could provide where I can locate this part would be appreciated!

 

[roni-wan]

Same problem here but still no luck finding that part

 

[aceofriches]

The pull and save yard here has a few DSM's... if you want I can find you one next time im there (this week) and mail it... ill only charge for what ther junkyard charges plus shipping... im not makin any money--- anything to help a fellow DSMer

 

[roni-wan]

The pull and save yard here has a few DSM's... if you want I can find you one next time im there (this week) and mail it... ill only charge for what ther junkyard charges plus shipping... im not makin any money--- anything to help a fellow DSMer

That would be very nice from you