A/C Diagnosis? High pressure on both High & Low side.

[never_comment]

I have been troubleshooting this problem on my 2007 Audi A4 B7 (160k miles) for a couple weeks and have hit a dead end.

Problem: If I idle too long like at a light too long the A/C starts blowing hot humid air. Otherwise at speed the A/C works fine (not great, but fine).

Troubleshoot:

• I found this fault using VCDS: "00819 - High Pressure Sensor (G65) 06-00 - Signal too High"
• Replaced G65 High Pressure Sensor hoping for an easy fix.
• Measured the low pressure side with a recharge can gage and saw ~100psi on the low side when idling.
• Compressor Works/Idle Pulley seems to work (hard to tell)
• Took log using VCDS of my car and friend's working car (A4 B7) located at this link and saw obvious differences in the HVAC during idle: https://docs.google.com/spreadsheets...it?usp=sharing

From what I can tell from the logs, the pressure on my car is defiantly gets too high then shuts off the air conditioner. This happens over and over and over at idle but not at any speed. You can hear and feel it in the car when the A/C turns on and off, it is like a heavy load is being taken on and off the motor and the car shakes more than normal. The 'good a/c' car does not do this at all. The A/C unit has never been touched previously (no recharges). I have not been able to find someone with a similar problem on this or other Audi forums. Any direction/help would be greatly appreciated.

[Brillo]

You may be overcharged with refrigerant and/or your condenser fan(s) may not be functioning as it should when the car is stationary. When moving, the flow of air increases greatly, properly cooling the condenser coils. Also, is the heater fan inside the car pushing a lot of air when on full blast? Check this by measuring the vent temperature on full blast when moving down the road (not on recirculate mode)? As a very general rule of thumb to check overcharging or malfunctioning airflow over the evaporator coils drive down the road with the system on full blast (not on recirculate mode), stop the car and immediately pop the hood, hop out and feel the temperature of the evaporator outlet pipe at a point closest to the firewall. If it is cold to the touch you are possibly overcharged or not not getting enough airflow over the evaporator coils. You might also have significant air contamination in the system. Personally, AC is one thing I usually don't mess with. I would urge you to have the system checked by a professional. Prolonged overpressure will kill your compressor and then you're out a lot of money!!

[never_comment]

You may be overcharged with refrigerant and/or your condenser fan(s)...

Everything you said but being overcharged sounds like a possibility. There has been no A/C work performed on it, so the system has never been added to. I will report back.

Sent from my Pixel XL using Audizine mobile app

[never_comment]

You may be overcharged with refrigerant and/or your condenser fan(s)...

Checked the temp of the outlet pipe at the firewall and it was not cold immediately after driving (inlet pipe was very cold, but I guess that is expected).

How would one check the fans across the condenser? At this point that makes the most sense, since the system works at any driving speed and stops working when stopped for more than 30 seconds or so.

[Gin+]

The lazy approach would be if you sit in the driver seat with the window down and press the econ button you should hear the fan switch off. That said, you should also hear it turn on when you turn off econ mode.

[roboto_1337]

Take it to s shop and have them evac the system and see how much r132a you have. If your at least 80% full it sound like you have the same problem I had.

Replaced compressor, drier, orifice tube, flushed and recharged. Works like new.


Sent from my iPhone using Audizine

[Brillo]

Checked the temp of the outlet pipe at the firewall and it was not cold immediately after driving (inlet pipe was very cold, but I guess that is expected).

How would one check the fans across the condenser? At this point that makes the most sense, since the system works at any driving speed and stops working when stopped for more than 30 seconds or so.

OK, good. The outlet pipe not being cold would verify what you said about the system not being overcharged. I don't know how to check the function of the condenser fans and the logic system that controls them. There is a recent thread called "AC is out" that you should check out. Veteran member Fly300kts has commented on the fan problem. It might be helpful for you to read that if you haven't already done so.

[never_comment]

I have found this to be very helpful though not for the exact car. Describes my symptoms to a 'T'. Looks like my condenser fan(s) is out. I need to find out how to fix that. The author makes me believe that if I don't do it quick my compressor is about to go.

http://forums.tdiclub.com/showthread.php?t=242699

[never_comment]

Is it possible to change out the radiator/coolant/condenser fans without putting it in 'service position.'

This guy does it on a A4 B6 with only removing the front bumper and headlights. If I can get away with that, it definitely seems worth it:

https://www.youtube.com/watch?v=wAJCTjW2BvA

Anyone with experience?

[never_comment]

So I thought my issue was my radiator/coolant fans which were both not running (though they spun freely). I cut insulation away on each lead wire to create Test Points. I measured 0V while running and 0 Ohms when off. My thought was if the motors have 0 resistance than they are hosed and will not have a voltage to measure across them. Boy was I wrong.

So I cut one lead wire to Passenger Side Fan/Motor so that I could measure the voltage that the control module was sending out. When I turned the AC ON Full, the Driver Side Fan/Motor started to spin (Hazzah!) and the PS Fan/Motor measured 7-10V across cut wire. So my theory now is that the PS Fan was causing an over-current and the control module was shutting them both down. My only issue with this theory is that I would expect to see a fault on the VCDS. Any ideas? Should that throw a fault? Any more testing I can do?

Here is a electrical diagram and summary of what I measured:

http://imgur.com/a/hao2X

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