A/C issues.....

[mdh]

So I have the typical econ button coming on problem, only mine isn't because of low pressure... I have over 100psi static in the lines. I get power thru the pressure switch and everything, but no power to the plug on the compressor. I have tried all the fuses, and I only have like 4 relays in my entire car... none of which appear to control the A/C compressor... I don't know what to do now. Everything works, but for some reason something is not allowing power to be sent to the compressor.

[eljay]

Any fault codes stored?

[jacobsen]

Are you overcharged?

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[mdh]

I have the ebay VAG-Com cable, and never could get it to work, so Im going to see if a local audi guy will let me borrow his to run VAG codes... but as far as OBD2 codes you can check at vatozone, nothing.

Jacobsen- I don't know... I can't get the compressor to come on to get a true reading, all I know is that static pressure is 100~psi in both lines. So there IS pressure there.

I had to rebuild a bunch of this car when I bought it, in doing so I had to evacuate the A/C system. I got it all put back together, got the A/C recharged at a shop professionally and everything was great, all the sudden one day the A/C just quit on me... ECON button came on, no A/C. The other day I had the car pulled back apart again to fix a couple minor issues and to swap the turbo out, and when I got it all back together, I started the car and after letting it run for a few minutes I decided just for giggles to turn the A/C on, it kicked on and ran like a champ, cold as ever. After a few minutes it shut off. Now it's back to not coming back on...

So I assumed I had a leak in the system causing it to be a low pressure problem, we threw manifold gauges on it and it read 100~psi on both sides. Power into and out of the pressure switch, signal and everything, ground wire runs good, just no power to the plug on the compressor... none. At all. All the fuses are good..... I don't get it. lol

[Kevin C]

If your motor has been running and parts of your AC are up to engine temperature, you should see more than 100 PSI. If the car has sat and allowed to completely cool, than you should see 100 PSI on an 85° day. If I remember right, with a warm engine I had about 140-160 PSI.

Once the compressor kicked on low was like 35 PSI, and high was in the 150 range.

100 PSI should be enough to allow the compressor to activate, so it still does sound like an electrical issue. Also, the signal to the compressor is a PWM that varies the output of the compressor.

[mdh]

Well at first the system had 120~ in both lines, we let a smidge out and its now sitting statically at about 105-110 between the two lines... it didn't change much but this was a 90-93 degree day and we did it in the evening. Car was warm the entire time.

So where does this signal come from that runs to the compressor? Is it coming from a control module of some sorts or a relay or what?

I also noticed that there is an Air Temperature Sensor or something like that, which is attached to the EVAP box under your cabin filter, could that play part if that freaks out?

[jacobsen]

You need to follow that electrical connection back and determine the condition of the line. Do you get continuity in the line?

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[ecjr173]

I had the same issue. My Econ light was on all the time. Turns out this sensor was bad. Coolant blew right through it. Blew the electrical connection right off.




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[mdh]

Jacobsen - Testing the ground wire, it reads fine. We get solid ground all the way to the plug, but the power wire, gets nothing... period. I've followed the wire back to the firewall, and nothing. There is no signal going thru that line.

ecjr173 - thank you, but we have done multiple tests with a multimeter checking the plug and the switch and have concluded that it's ok...

[old guy]

When you turn the AC to the on position does the condenser fan turn on? I'm pretty sure that if the fan doesn't turn on the AC will not engage. It could be a problem with the fan control module. At least that's true on some of the later model A4s. Not sure about an 02 model.

[jacobsen]

That's gotta be it

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[mdh]

That would make sense... I'll check that this evening after work and see, because no, they don't turn on. Nothing happens... just illuminates the econ mode.

[mdh]

So after trying to figure this out, I'm not sure what you mean by condenser fan. I have dual radiator fans, but they are side by side, behind the radiator and condenser. They are both running already before I even turn my AC on, and when I attempt to, they just stay running... I'm hoping that by tonight I can get my cheap china crap VAG cable installed right so I can connect thru VCDS and see if I can pull some codes on what is causing this, but as for now, I'm at a loss...

[5ktq]

When the engine isn't hot and the A/C is off, the fans shouldn't be running. Even if the engine is cool, when you switch on AC, they fans should kick in. If they don't, the compressor won't either. (at least on mkiv golfs... I'm pretty new to B6).

So maybe the radiator temp sensor is shot if they run all the time. I think that's generally a two stage thing on most cars. First stage is low speed / need some cooling, but not a big deal. Stage two for overheating imminent, enter warp drive. Often cars will kick off the compressor during this to help with cooling. So.. maybe your switch is in permanent near-overheating mode and has disabled the AC for that reason..? Just some things to consider, not sure if it works that way on this one. Do the fans blow like crazy or low speed.

[mdh]

Would that not make my tempterature gauge on my dash show that it's hot then though? It warms up gradually just like normal and reads middle of the gauge after it's warm just like it always has... It's definitely something to check out, but I would figure that it would show some fluctuation in the temp gauge on my dash right?

Also the fans seem to never kick into warp speed... just stay at a normal relatively low speed.

[jacobsen]

Would that not make my tempterature gauge on my dash show that it's hot then though? It warms up gradually just like normal and reads middle of the gauge after it's warm just like it always has... It's definitely something to check out, but I would figure that it would show some fluctuation in the temp gauge on my dash right?

No

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[mdh]

So then that is a different coolant temp sensor that's connected to the gauge on my dash? The radiator temp sensor is different?

[5ktq]

Yeah. There's a green one at the back of the engine (4 pin). That one is for ECU and the instrument panel, afaik.

There's a 2 pin one on the lower rad hose , on the quick coupler, that one must be for fans.

[mdh]

Well the one on the waterneck behind the head is brand new, the one on the lower radiator hose could be faulty I guess... It is original. I may pick one up today and see if that does the trick....

Do people ever have gunk build up on that sensor causing it to have issues or anything? Being that it sits kinda at the bottom of the loop where sediment if any in the system could gather?

[diagnosticator]

Well the one on the waterneck behind the head is brand new, the one on the lower radiator hose could be faulty I guess... It is original. I may pick one up today and see if that does the trick....

Do people ever have gunk build up on that sensor causing it to have issues or anything? Being that it sits kinda at the bottom of the loop where sediment if any in the system could gather?

Coolant flow velocity does not allow sediment to collect around the temp sensor in the lower rad hose.

[mdh]

Well that would make sense, I unplug that sensor to drain the system because its the easiest and works the best, and never had anything but bright pink coolant come out. Maybe I messed the sensor up when I did so... Idk.

[diagnosticator]

Yeah. There's a green one at the back of the engine (4 pin). That one is for ECU and the instrument panel, afaik.

There's a 2 pin one on the lower rad hose , on the quick coupler, that one must be for fans.

You are mostly correct, the lower rad hose sensor output is used by the ECU to run the driver's side rad cooling fan when the coolant leaving the radiator is to hot, needing more cooling fan air flow to cool the coolant more. The ECU sends a PWM voltage to the fan control module to command the fan ON, and vary the fan speed as needed according to the coolant temp sensed by the sensor in the lower rad hose. The rad fan can run under variable speed depending on engine load and ambient air temps, or for lower load and engine speed regular driving, slow speed of the fan will cool the coolant enough for the ECU to turn the rad fan OFF after the coolant is below the fan ON temp.

The AC condenser cooling fan is the smaller fan on the passenger side, and runs slow when the AC is in AUTO or Manual mode. The AC fan does not run with the AC in ECON mode. The AC condenser cooling fan is controlled by the HVAC controller in the dash.

The fan control module has two separate fan speed control modules inside, one for the the rad fan, the other for the condenser fan. The two fan speed controllers are independent of each other, contained in the same housing and share some electronics, but command and control is separate for the two fans.

[diagnosticator]

So after trying to figure this out, I'm not sure what you mean by condenser fan. I have dual radiator fans, but they are side by side, behind the radiator and condenser. They are both running already before I even turn my AC on, and when I attempt to, they just stay running... I'm hoping that by tonight I can get my cheap china crap VAG cable installed right so I can connect thru VCDS and see if I can pull some codes on what is causing this, but as for now, I'm at a loss...

The driver's side rad cooling fan should not be running after staring the engine. If it is, then there is something wrong with the cooling system as monitored by the ECU. If a cooling system DTC is stored, results with the rad fan starting up and running at high fan speed when the engine is first started from cold, then slows down as the ECU senses the coolant temp is in control, and not overheating. After the engine is up to operating temps, the ECU does not command high fan speed at start up again. If there is a cooling system DTC stored, then the engine ECU sends an AC compressor OFF signal to the HVAC controller that places the compressor in the zero output mode, and turns ON the ECON mode light. ECON mode cannot be deselected if there is a cooling system fault DTC stored, or if the compressor is locked out in ECON mode due to under or over-pressure in the AC system.

The AC condenser cooling fan should start up and run at slow speed after starting the engine, with the AC in AUTO or Manual mode. The condenser cooling fan will not run with the compressor OFF in ECON mode.

[diagnosticator]

Jacobsen - Testing the ground wire, it reads fine. We get solid ground all the way to the plug, but the power wire, gets nothing... period. I've followed the wire back to the firewall, and nothing. There is no signal going thru that line.

ecjr173 - thank you, but we have done multiple tests with a multimeter checking the plug and the switch and have concluded that it's ok...

The AC pressure "switch" is not an actual ON/OFF switch, it is a variable resistance pressure sensor.

[mdh]

Your wealth of knowledge amazes me. Thank you. I will be checking into this deeper this evening, when I go to leave work. My car will be cool so I will see what it does from a fresh start.

From what you're telling me though, the passenger side fan should not run unless the AC compressor is on? Meaning if my car is in "Econ" mode, that fan should not run? Because, the night before last when I got home from work and popped my hood, granted, the car was at operating temp, both fans were running at a lower speed. Not like really low, but not in their "warp" speed as we called it earlier. Just at a normal speed.

Given that this is the case, and something is wrong with the cooling system, where should I look to find the culprit? I feel like I've looked at everything everywhere.

[mdh]

So this morning I checked from a cold start my fans did not run. Neither of them. It idled, warmed up and everything with no fans running. Tried turning my AC on, nothing, no fan, no compressor, ECON button.

[mdh]

So I got my china vag-com cable to work with VCDSlite and purchased the registration for the program... freakin $100..... anyways. Until I get my activation code, I can't read what the other fault is but there are 2 faults in my "AUTO HVAC"... one is an Air Quality Sensor. Cant that play part? There is another code but it's not letting me view it until I get my activation code from Ross-Tech.

[5ktq]

The shareware version still says the code, ie. 17544, and then says - not registered - so it doesn't tell you what it is directly.

But you can punch that code into google and find out what it is.

[mdh]

Thank you sir. Hahaha I'm about to run do that then.

[mdh]

So I got my VCDS activated and everything, came up with a High Pressure Switch code and an Air Quality Sensor...

[Kevin C]

So I got my VCDS activated and everything, came up with a High Pressure Switch code and an Air Quality Sensor...

My take is that you're either over-charged or have blocked flow to the condenser or the pressure sensor is giving you a false reading. Does a one time event with a code permantly disable the AC until the code is cleared? A blockage on the high side could cause the same issue.

[BumblebVR6]

So I got my VCDS activated and everything, came up with a High Pressure Switch code and an Air Quality Sensor...

My $$ is on the high pressure switch. Just had the exact same issue/code pop up. Sure enough, the switch was already leaking freon thru it. Replaced w/ a new sensor (3R0 959 126), cleared code, and started the car. Blew hot air at first, no more ECON light. System was low on freon so I recharged and bam! Back in business. Most likely your issue since you have a code for the switch. Mine was original, 11 years old.

[jacobsen]

So you have to release the gas from the system in order to change the pressure switch? Op take it to a shop if need be, don't pollute.

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[mdh]

The code says "Short to Ground" on the high pressure switch. Tested the ground with a meter, read fine... gonna maybe attempt to just run a temporary ground to the frame and see if that fixes it, if not, replacing the sensor... :/

I doubt I overpressured it, it was done at a shop professionally and worked for 6-8 months.... then one day stopped... then after I pulled the car apart to fix some other issues and got it back together it came back on briefly then stopped again. lol Faulty switch or bad ground I'm sure...

[BumblebVR6]

So you have to release the gas from the system in order to change the pressure switch? Op take it to a shop if need be, don't pollute.

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Negative. The connection port on the condenser has a schrader built in which is depressed once the switch is threaded onto it.

[jacobsen]

Negative. The connection port on the condenser has a schrader built in which is depressed once the switch is threaded onto it.

Awesome

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[rocket1420]

The code says "Short to Ground" on the high pressure switch. Tested the ground with a meter, read fine... gonna maybe attempt to just run a temporary ground to the frame and see if that fixes it, if not, replacing the sensor... :/

I doubt I overpressured it, it was done at a shop professionally and worked for 6-8 months.... then one day stopped... then after I pulled the car apart to fix some other issues and got it back together it came back on briefly then stopped again. lol Faulty switch or bad ground I'm sure...

Before you change some parts, clear the codes and see what happens.

[Kevin C]

The code says "Short to Ground" on the high pressure switch. Tested the ground with a meter, read fine... gonna maybe attempt to just run a temporary ground to the frame and see if that fixes it, if not, replacing the sensor... :/

I doubt I overpressured it, it was done at a shop professionally and worked for 6-8 months.... then one day stopped... then after I pulled the car apart to fix some other issues and got it back together it came back on briefly then stopped again. lol Faulty switch or bad ground I'm sure...

When you ohm out the high pressure sensor, what does it read?

[mdh]

When you ohm out the high pressure sensor, what does it read?

Well the issue with that is that it's not actually a typical high pressure sensor, it's a variable resistance switch. So I'm not sure now...

[5ktq]

Yeah, the sensor puts out some sort of digital output relative to the pressure (varying duty or frequency of pulses, would be my guess, I've never scoped one).

The "Short to Ground" is in reference to the output signal, now whether that means the output pin is actually short to ground or if it's just low (no output). You'd think then you'd get "signal too low" but the codes are weird sometimes.