No A/C and at my witts end over it

[53heloFE]

The A/C has not worked in the car since I purchased it last August, and along with some other common CCU problems so I replaced it. After CCU replacement the A/C still did not work but all is operational on the CCU aside from that. I chalked it up to possibly low refrigerant. I took it and had the A/C charged last month, they had to jump the system to get the compressor engaged to take the refrigerant. I watched all of this and the system is now charged and has no other mechanical problems.

I have run the troubleshooting trees in the service manual, three times now too, for both A/C doesn't engage and the one for A/C and condensor fans do not come on. And no the condensor fans do not turn on when I turn on the A/C nor does the engine idle up for the load that should be put on the engine. I have checked and rechecked wirers per the troubleshooting trees and everything that is suppose to have voltage does and everything that is suppose to have continuity does. The compressor engages when the proper wires are grounded. I even ran the tests from the CCU with no indicated failures.:frown:

I have replaced the fan control unit with no luck, replaced the relay and swapped relays around just in case but to no avail. Even the condensor fans will run if I put voltage to them. I checked power accross the relay box and bypassed the relay at the relay box and the compressor and fans came on.

Does anyone have any suggestion that might not be in the manual that I can try, or something that is a little different than the manual. I am at a total loss as to why this thing will not turn on.

Much thanks to BrianK for all of the help he has given me, for taking my CCU and testing it on his bech and in his car.

Maybe I am not rubbing my belly and patting my head in the right direction:biggrin:

 

[Zennsx]

Possibly your low on freon? Clutch for AC wont engage if undercharged.

 

[drew]

You should monitor the pressure in your system as a reasonable start.

There is also a triple switch in the front compartment (near cruise control?). Monitor the inputs and outputs from the switch...I've had them go out in other cars.

Drew

 

[Briank]

We know your CCU is good so start over at the CCU and confirm the AC request signal is working. 0 is on and 12v is off. Grey/black pin 2 or at pin 4 at the cooling fan control unit.

 

[D'Ecosse]

Looks to me like your Triple Pressure switch is inhibiting things - that is the primary interlock for both condensor fans & compressor clutch. I would not suspect a problem with the switch or wiring, more likely fundamentally that you have no Freon - there is probably a gross leak somewhere.
You could test by grounding the input to the fan control module & see if the condensor fans run & A/C compressor clutch pulls in (don't run the engine, ignition only). To do this, disconnect the plug from the pressure switch & connect a jumper between the BRN/BLK & BLK wire terminals.

 

[Zennsx]

Take the cap off the charging schrader valve(low suction line) and depress the pin momentarily,( like you would let the air out of a tire ). You probably have little or nothing in there.

 

[53heloFE]

You should monitor the pressure in your system as a reasonable start.

There is also a triple switch in the front compartment (near cruise control?). Monitor the inputs and outputs from the switch...I've had them go out in other cars.

Drew

Drew,

How can I go about monitoring the inputs and outputs of the triple pressure switch? Should I be looking for continuity on the brown or the black with it connected to the pressure switch?

 

[53heloFE]

Take the cap off the charging schrader valve(low suction line) and depress the pin momentarily,( like you would let the air out of a tire ). You probably have little or nothing in there.

I have pressure on the low and high side. I had the system evacuated and leak checked, and then serviced up. I thought it was originally just low and wanted to make sure everything was tight before having it serviced. The mechanical part of the system passed and held vacume. Though we had to trick the compressor into running so that we could get the freon in the system.

 

[MiamieNeSeX]

How did they shop bypass and charge the system? It might just be the high pressure switch.


Armando

 

[D'Ecosse]

Drew,

How can I go about monitoring the inputs and outputs of the triple pressure switch? Should I be looking for continuity on the brown or the black with it connected to the pressure switch?

Not Drew, but I think I already answered this before you asked it ......

You could test by grounding the input to the fan control module & see if the condensor fans run & A/C compressor clutch pulls in (don't run the engine, ignition only). To do this, disconnect the plug from the pressure switch & connect a jumper between the BRN/BLK & BLK wire terminals.

Conversely you can check for continuity between the corresponding terminals of the switch.

 

[53heloFE]

Looks to me like your Triple Pressure switch is inhibiting things - that is the primary interlock for both condensor fans & compressor clutch. I would not suspect a problem with the switch or wiring, more likely fundamentally that you have no Freon - there is probably a gross leak somewhere.
You could test by grounding the input to the fan control module & see if the condensor fans run & A/C compressor clutch pulls in (don't run the engine, ignition only). To do this, disconnect the plug from the pressure switch & connect a jumper between the BRN/BLK & BLK wire terminals.

I have plenty of freon in the system, but it should not be over charged though since iI know this will cause the system to not work also.

Per the manual if I disconnect the pressure switch and jump the BRN/BLK to the BLK it says to move on to the next step if the clutch does not engage and I have continuity in the wires. So according to the manual if the clutch engages then the pressure swith is bad.

I have tried this with the engine running, engine running A/C off, engine running A/C on and the clutch still does not engage with those two wires jumpered.

 

[53heloFE]

We know your CCU is good so start over at the CCU and confirm the AC request signal is working. 0 is on and 12v is off. Grey/black pin 2 or at pin 4 at the cooling fan control unit.

Brian

I measured the voltage at the fan control unit for the grey/black, blue/black, blue/red and red/blue on the ECU both with the A/C on and off. The voltage on the volt meter never went to 0 on any of the wires, it stayed battery voltage the whole time

I even shook the connectors to see if that might be the problem but it never changed any result.

 

[53heloFE]

How did they shop bypass and charge the system? It might just be the high pressure switch.


Armando

They put battery voltage to the clutch and ran the compressor that way. Just to make sure it was not too high I just hooked up my pressure gage to the low side and jumped the relay to get the compressor to run. It did not show too much pressure, if anything maybe just a bit low. For the low pressure switch to kick in and cut out the system it has to be near empty and it is nowhere near that low.

 

[53heloFE]

Not Drew, but I think I already answered this before you asked it ......


Conversely you can check for continuity between the corresponding terminals of the switch.

I thought you two were talking about different checks for the triple pressure switch. I have continuity in the brn/blk and the blk to their respective connections. I was thinking maybe checking the switch to ground to see if it is open or closed. I just don't know what pin on the switch its self should be open or closed for a properly filled system.

I have grounded the fan control and the compressor runs, but that does not make the fans come on.

 

[Zennsx]

They put battery voltage to the clutch and ran the compressor that way. Just to make sure it was not too high I just hooked up my pressure gage to the low side and jumped the relay to get the compressor to run. It did not show too much pressure, if anything maybe just a bit low. For the low pressure switch to kick in and cut out the system it has to be near empty and it is nowhere near that low.

While recharging my system the compressor wouldn't come on until I hit something like 19 ounces , If my memory serves me correctly.

 

[53heloFE]

I REALLY appreciate everyones inputs to me on this. I am at such a loss I will pretty much go out and try anything suggested that might help me figure out why the A/C will not work. I think I have run out and checked just about everything you fine folks have posted.

I just ran the idle checks in the manual and they passed. So I was checking voltages on the yellow/black and orange black from the fan control unit and never had a change in voltage with A/C on or off.

I wonder if it is my ECU that is causing the problem? That is a pretty expensive part for me to just order one without knowing though, or being able to put a known good one in to see if that fixes it or not. Anyone know where I could borrow and ECU to test?

 

[D'Ecosse]

......I was thinking maybe checking the switch to ground to see if it is open or closed. I just don't know what pin on the switch its self should be open or closed for a properly filled system.........

What I meant above was - to test if the switch is what is causing the interlock for the system not running, disconnect the plug from the Triple Switch & short a jumper link across the terminals to which the BRN/BLK & the BLK wires connect then re-test.

To check the condition of the switch, remove the connector from the switch - identify the terminals that the BRN/BLK & BLK wires would be connected to with the plug in place - check for continuity between those pins. It should be short circuit (virtually zero ohms). If open, then you have a freon pressure problem or a bad switch.

.... So I was checking voltages on the yellow/black and orange black from the fan control unit .....

Huh??? YEL/BLK & ORN/BLK on FCU???????

I have grounded the fan control and the compressor runs, but that does not make the fans come on.

When you say "grounded the fan control" are you talking about the input from the pressure switch (BRN/BLK) or the outputs to the condensor relay (ORN/BLU) & CCU (BLU/BLK)
Disconnect the FCU plug
Ground each of the outputs ORN/BLU & BLU/BLK which should respectively activate the condensor fans (both) & the compressor clutch - can you report on whether this does? (Use a wire link to direct short between the pin of the plug & true ground - chassis)
Ensure your CCU is turned on with ignition & the demand is set for A/C at 60 during this test ....

 

[53heloFE]

What I meant above was - to test if the switch is what is causing the interlock for the system not running, disconnect the plug from the Triple Switch & short a jumper link across the terminals to which the BRN/BLK & the BLK wires connect then re-test.

To check the condition of the switch, remove the connector from the switch - identify the terminals that the BRN/BLK & BLK wires would be connected to with the plug in place - check for continuity between those pins. It should be short circuit (virtually zero ohms). If open, then you have a freon pressure problem or a bad switch.




Huh??? YEL/BLK & ORN/BLK on FCU???????



When you say "grounded the fan control" are you talking about the input from the pressure switch (BRN/BLK) or the outputs to the condensor relay (ORN/BLU) & CCU (BLU/BLK)
Disconnect the FCU plug
Ground each of the outputs ORN/BLU & BLU/BLK which should respectively activate the condensor fans (both) & the compressor clutch - can you report on whether this does? (Use a wire link to direct short between the pin of the plug & true ground - chassis)
Ensure your CCU is turned on with ignition & the demand is set for A/C at 60 during this test ....

I haven't figured out how to do the multiple quotes in one reply man so I will start from the top.

I disconnected the pressure switch and checked continuity from the brn/blk and blk terminals of the switch its self and that is good. So that contact is closed and should rule out it being the switch or a pressure problem right.

Thanks for correcting me on the org/blk thing I meant org/blu. Also there is a blu/red. Both of which will turn the condensor fans on if I ground them out along with the blu/blk turning on the compressor. I did this with the connector disconnected and the results were the same CCU on or off.

Last night I was testing to see if voltages were changing on some of the other wires with the A/C on or off. It seems as though what is suppose to tell the system to turn on is not working somewhere in the system. Like BrianK said, we know my CCU is good, it worked in his car.

I iwsh I had more than the simplified wiring diagram that is in the service manual.

 

[Briank]

Brian

I measured the voltage at the fan control unit for the grey/black, blue/black, blue/red and red/blue on the ECU both with the A/C on and off. The voltage on the volt meter never went to 0 on any of the wires, it stayed battery voltage the whole time

I even shook the connectors to see if that might be the problem but it never changed any result.

I guess you need to go back to the CCU pin 2 Black/gray see if the AC request signal is there.

 

[53heloFE]

I guess you need to go back to the CCU pin 2 Black/gray see if the AC request signal is there.

Ok I will try that. How do I do that again???

 

[Zennsx]

Did you check yor evaporator temp sensor? Page 22-68 of service manual.

 

[Briank]

Ok I will try that. How do I do that again???

With the ccu in the car and connected you need to back probe the black/grey wire pin 2 on the big connector and mesure the voltage to ground. I assume your meter probe will not fit in the back of the connector so you will have to use a piece of wire to poke in the back of the connector.

Not the best picture but it should help you locate pin 2.

 

[D'Ecosse]

T.... I meant org/blu. Also there is a blu/red. Both of which will turn the condenser fans on if I ground them out along with the blu/blk turning on the compressor. I did this with the connector disconnected and the results were the same CCU on or off. .

The BLU/RED is actually the engine compartment fan; the ORN/BLU is for the condenser fans; (I assume you are just hearing the fans turning on?)

I just found another portion of the Triple switch - the contacts between BLK & RED/ORN should be OPEN - if these are closed (short circuit) then that is the low pressure signal which should inhibit the ECM.
However, just disconnecting the plug from the triple switch & shorting out the BRN/BLK to ground should eliminate this anyway.

According to the logic diagram on page 22-8 of my manual when the Triple Pressure Switch is closed (i.e. BRN/BLK wire shorted to ground) then the ECM output (BLU/BLK) should also go to OV (ground potential) & the compressor should run. (When the blu/blk O/P is "high" the compressor should be off)

So - if I read your statement in the quote correctly, the compressor runs when you ground the ECM O/P from the FCU; therefor, if it does NOT run when you have grounded the BRN/BLK input to the FCU (with the A/C demand on - (GRY/BLK must be "low") then the FCU must be bad.

Verify that when you demand A/C (selected on CCU & temp at 60), & ignition is on, you should have "LOW" at GRY/BLK; you also should have a "LOW" at the BRN/BLK - these input conditions should give "LOW" output on both the ORN/BLU & BLU/BLK outputs.

Somehow I still feel you are not getting the 'go' from the TPS i.e. the BRN/BLK is not at "LOW".

If your GRY/BLK is not at 0V however that takes you back into your CCU (which was verified good, correct?)

Edit Looking at this again this morning, it could be your radiator fan water temp control sensor? Have you noticed, does your radiator fan work normally? You could try blowing on the water temp sensor with a heat gun & see if it kicks in, first on low speed, then on high as it gets hotter. Measure the voltage across the LT GRN & BLU/WHT wires at input to the FCU - it should be increasing as it gets hotter. If that responds normally, then that probably rules out that input to the FCU as being the culprit.
If your radiator fan is running all the time, it also probably says that sensor is either disconnected or bad.

 

[53heloFE]

Just a quick update. I have been sick so I have not been up to working on the car all week. The only thing I did was send out my "new" fan control unit to be tested in anothers NSX. I will keep the board updated after I complete some more of the tests posted for me to try.

 

[53heloFE]

Brian,

I used a jumper like you said from the back of the CCU connector and measured voltage from there with the a/c on and off illuminated on the display with no change in voltage, it remained battery voltage the whole time. If I connected the jumper to ground the condensor fans would come on and the compressor would engage.

I was thinking perhaps my connector is bad so I used a good light to see if there is any trash in the plug keeping the signal from getting past the connector but it looked ok. I pushed the back of the pin to make sure it is seated in the connector and also wiggled the wire around with the a/c on to try and get it to kick in but that did not help either.

Where do I do next

With the ccu in the car and connected you need to back probe the black/grey wire pin 2 on the big connector and mesure the voltage to ground. I assume your meter probe will not fit in the back of the connector so you will have to use a piece of wire to poke in the back of the connector.

Not the best picture but it should help you locate pin 2.