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

 

[miguelmcv]

Bringing this back from the dead. Before I test voltage on the ACCU, does anyone know the answer to this question?

I have power to one pin on the relay connector, but not on any of the others to turn the compressor on. If we jump the connector the compressor kicks on and blows cold air. I have thought of just wiring in a switch like above but would much rather fix it correctly. Any ideas before I start testing the things stated in this thread? Somewhere I should start perhaps?

OK, The current passes to the refrigerant Temperature sensor, then passes to the relay and triggers the Compressor, If the Refrigerant Temperature Sensor is bad or is not hooked up, it will not trigger the relay to turn ON the compressor, If you are saying that the relay doesn't get current, then check you Refrigerant Temperature Sensor, (post #40 shows the RTS).
Make a jump wire from the wiring on the RTS Connector and see if the compressor kicks, If it kicks, replace the RTS,..
There is a post in this thread saying the RTS is not replaceable, IT IS REPLACEABLE , I replaced mine with a good used one, However, I don't know if it is available by it self, or you need to buy the complete compressor, But at least we know we can replace RTS by it self with a used one.

 

[chrysler kid]

I've also been wrestling with the MB946485 controller for a few days now. I hope this helps someone else out. After pouring over the wiring diagrams for the controller for a while and playing with a multimeter for a few hours, we now know the following:

1. MB946485 is a controller for DSM air conditioners that were manufactured with the two-step econ/regular button. I don't believe DSM's with the one step use this controller, as they use the newer type controller instead. (If anyone has ever seen otherwise let me know). The MB946485 has two inputs (blue, and blue/black wire), one for economy A/C, and one for regular. One wire is set to +12v for economy mode, and both are +12 for normal mode.

2. The adjustable dial on the MB946485 seems to control the temperature differential between regular and economy modes. (Based on my limited understanding of reading circuits) See: 2g Eclipse Tech Info Manual Pages 7-36 and 7-38

3. MB946485 has TWO temperature sensor inputs, one for air temperature, and one for fin temperature. The fin temperature test from the shop manual works, but I cannot find one for the air temperature sensor. They do output separate readings, and are quite a bit off. The tech manual is the only proper documentation that I can find on this. My car has both sensors, and they both lead into the cooling unit, and are sealed with RTV.

4. The four yellow wires on the left hand side of the harness represent the two temperature sensors. The two wires that are closes together represent one sensor.

5. There are two grounds on the harness (black wires)

6. The red wire on the harness provides power to the unit.

7. The green wire with the orange stripe is for output of both the A/C fan relay, and the loop that goes in the following order: Dual Pressure Switch > A/C Temp Sensor (compressor) > ECU. If you have a sensor that is not reading ON, then the A/C clutch will not engage. The A/C clutch binary value in DSMLink will be set to 0. With this controller, however, the A/C fan relay will be turned on regardless of whether the A/C clutch is engaging.

8. If you wish to test the circuit without the MB946485, simply unplug the harness and take a paper clip and plug it into the red and green/orange wires. The two temperature sensors will be bypassed and allow you to check out other sensors.

9. The MB946485 is a STURDY animal. Mine was acting a little strange, so I pulled the casing apart and found some corrosion between two of the solder pads. I cleaned the traced and pads up with acetone, and the controller ran like it was brand new.


I've now tested everything in my A/C loop with the exception of the compressor temperature sensor. Anyone have any good ideas on how to test or replace that sensor that doesn't involve taking half my car apart? I'm about to drop my t-case and look at it from the bottom, as there isn't much room in the upper part of my engine bay.

Good luck!
Matt

I live in Texas and I've verified my high and low side pressures are correct but my compressor cycles every 30 seconds or so inconsistently.

I plan to jump the wires to bypass the temp sensors. With a black dash and black leather the temp sensors are not adequate in determining cabin temperature .

I would assume the temperature switches are for comfort and safety, but extreme conditions cause issues with under dash readings compared to actual cabin temps.

 

[MattHDSM]

I hate to revive such an old thread, but it seems like my issue and solution is closely related to what has been discussed in this thread and could help someone else down the line as these parts start to get older and die more often.

If your A/C Control Unit (ACCU) is dead (and your A/C is deleted) and you still want to use the A/C switch or defrost setting to turn on the condenser fan, you can jump the blue/black and green/orange pins of the ACCU pigtail to bypass the ACCU itself to power the condenser fan LO relay. For the sake of clarity, on my factory wiring, doing this only draws 200mA (at battery voltage) and from what I can tell does not pose a fire hazard based on my experience so far, but anybody considering doing this should check how much current is being drawn in their setup and make an educated decision themselves.

If anybody has a working ACCU, I would love to know the current and voltage output (from the green/orange wire) to see what is actually supposed to be triggering the condenser fan LO relay.

 

[waltah]

A few words about the compressor temp. sensor: It is a switch -- closed for normal operation but open to shut off A/C if compressor overheats. Access is impractical with the compressor on the car -- it's on the rear of the car (i.e. left) side of the engine under the intake manifold and as I recall it's very difficult to even get a hand along the top of the compressor to feel that the connector is in place. The switch can be replaced only with the compressor out of the engine or maybe with the intake manifold and probably other stuff removed.

It's pretty easy to test though. There should be continuity from one of the coil pins on the compressor relay (pin 3 actually) to the pin with the white/green wire on the dual pressure switch on the A/C filter/dryer.

The most common failure of the compressor temp switch is a wiring fault. The flat plug pushes down onto the connector on the compressor; it is easy to smash this when installing the compressor. Or it can just come loose if the wiring is tugged or ???

If this unit or wiring fails I personally would consider just jumpering it if the car is not driven hard or in extreme climate. I don't know of a single other Mitsubishi in those years that has this switch -- the refrigerant pressure switch (dual or sometimes triple pressure switch protects against most high temp situations in the A/C system. Yeah, if you're used to cruising at 120 downwind in Texas in the summer it's an essential safety backup but for most of us I have my doubts.

There are multiple different control units used in these cars. MB946485 is the original in GST and I think GSX. It uses two sensors -- one for the incoming air temp and one for the fin temp at the outlet of the evaporator. Another is MR227707. The 'R' tells you this is a replacement design; though it'll function in the same cars it uses only one of the two sensors -- the other has no connection on the circuit board. Either of these may be found in the GST and GSX cars. There are others, original in cars with only one sensor but also replaceable by the MR227707.

 

[waltah]

I live in Texas and I've verified my high and low side pressures are correct but my compressor cycles every 30 seconds or so inconsistently.

I plan to jump the wires to bypass the temp sensors. With a black dash and black leather the temp sensors are not adequate in determining cabin temperature .

I would assume the temperature switches are for comfort and safety, but extreme conditions cause issues with under dash readings compared to actual cabin temps.

The two temperature sensors on GST/GSX and some other models look at evaporator air intake temperature and fin temperature at the exit from the evaporator coils, i.e., icing. Cars with only one sensor have the icing one. Also the replacement ('MR') controllers may use only the icing sensor.

Icing of the evaporator isn't a safety problem but it will rapidly disable the A/C system as no air will be able to get through. So when the fin temp at outlet gets close to freezing, that sensor triggers the controller to turn the compressor off.

Compressor cycling at irregular intervals of 30 seconds +/- sounds like normal operation. In mild dry weather this will be done by the intake air sensor; in very damp weather by the icing one. This cycling is generally at intervals of 10 seconds or more for intake temp or 10 minutes or more for icing.

You drive off on a hot damp day, A/C is fine at first but after 20 minutes it seems really weak. You park, do your weekly shopping, come back there's a puddle of fresh water under the passenger side of the firewall. Drive off, A/C is blowing cold again. That's icing. The cause is either failure of that sensor or it was improperly installed when the evaporator was pulled due to dirt clogging or a leak. This sensor is often jammed into the fins on the outlet side but do this exactly as the book indicates.

Cycling of the compressor is abnormal when it's caused by low or high pressure at the dual pressure switch on the filter/dryer. Low pressure there indicates low refrigerant. Since the system oil is circulated by the refrigerant, operation with a low charge would destroy the compressor. The switch also opens on very high pressure which would indicate an overcharge condition -- risk of blowing something due to over pressure. These conditions can be detected by connecting a gauge to the high pressure side and watching it -- should be between 35 and about 150 PSI. Under 25 or over 200 or so, Sum Ting Wong.

The dual pressure switch is a safety feature -- never jumper it except for a quick test.

Cycling caused by dual pressure switch action is faster -- often just a couple-few seconds. But go by the actual pressure.