AC Help: Troubleshooting & Repair Experts

Hello,

I have a 1997 Passat 3B with an AFN engine and Climatronic.

My air conditioner has been malfunctioning since last summer. It's simply not cooling anymore.

That's why I had the air conditioning system serviced three weeks ago (including vacuuming, evacuation, and refilling). No improvement. Instead, the diagnosis was 'faulty air conditioning compressor.'

I had another (pressure) test performed at a BOSCH service center. The mechanics there also assured me that the compressor needed to be replaced.

Last week, I had everything vacuumed out again, replaced the air conditioning compressor and the dryer, added 250 cc of fresh oil, evacuated the refrigerant circuit, and refilled it with 700 grams of refrigerant.

And yet, there is still no cooling capacity. However, the pressures are now okay (with the air conditioning compressor at full load and an outside temperature of 21°C: 14 bar on the high-pressure side; 1.4 bar on the low-pressure side). The refrigerant pipes, however, remain warm (like the air temperature). How can this be? Pressure and refrigerant are present, but there is no temperature drop?

The CLIMAtronic system does not indicate any errors, and the temperature control flap is also being correctly adjusted (set to 'LO' for maximum cooling).

My workshop was at a loss and couldn't offer me an appointment any sooner than after Easter. What will this probably cost me?!


Perhaps someone here is familiar with this problem or has other suggestions. If anyone has any ideas, please let me know!

Is the compressor running?

You can tell by the rotating inner part of the pulley on the compressor. Does it also always make a 'click-click' sound when you turn it on and off?

If it pumps , there must automatically be a cooling of the liquid after the expansion valve (which is brass-colored on the right side of the injection molding machine, where the refrigerant is filled). Or, I suspect, that valve itself is defective.

Keep us updated. I've never heard of such errors before.

Yes, the compressor is definitely working. It's building up the pressure, which was measurable in the high-pressure line (14 bar).

Of course, there's also a clicking sound when I switch from ECON mode to AUTO mode (with air conditioning). The magnetic clutch engages then, which is understandable.

But if the throttle valve (the Passat uses this instead of an expansion valve) were broken, shouldn't the pressure behind the valve have dropped less rapidly (at 1.4 bar)? After all, that's the function of the valve itself, or am I mistaken?

I can only explain it by assuming we're measuring the pressure from something else in the pipes, perhaps air. Did the workshop perhaps cut corners when evacuating and refilling the system? There can't be any refrigerant in there if there's no noticeable temperature drop when the pressure decreases rapidly. That's physically impossible, right?

The air conditioner does cool, but only to a minimal extent, such that it only results in a 1°C temperature difference between the outlet temperature of the ventilation nozzle and the outside temperature.

The component immediately behind the throttle valve and the evaporator itself become quite cold, but only to about +5°C. The ND pipeline starting from the evaporator outlet immediately loses its temperature after just 5 cm.


The following is what I have tried:

'For the test, I removed the pollen filter, disconnected the cable from the fan, set it to fresh air and 'LO' mode, and drove off. It consistently ran at 55 km/h with 2000 RPM. At that speed, the air conditioning compressor was working at full load. Due to the small amount of airflow through the ventilation system, a constant draft of +6°C came out of my open ventilation vent. This means the evaporator was able to cool the 20°C outside air.'

However, when I plugged the fan back in, the temperature of the air coming out of the nozzle decreased proportionally to the fan speed, until at level 3, there was no cooling effect whatsoever.

The flaps (temperature, etc.) are also working perfectly. I checked the adjustment, and the diagnostic system for the climate control shows that the actual values of the flaps match the desired values, except for the outlet temperature of the center ventilation nozzles.

Set Point: 4°C
Actual temperature with wind chill: 6°C.
Actual value at fan speed 3: 19°C.

So, it can't be a problem with the electrical system.


Now I'm wondering what's causing this inadequate cooling performance. I pressed the OK buttons on both the low-pressure (LP) and high-pressure (HP) sides, the system was evacuated, and 700 grams of refrigerant was added.

Could it be that an excessive amount of refrigerant oil in the system is so severely hindering the heat exchange? The workshop's equipment could only extract a small amount of refrigerant (they said that not everything could be extracted), and the AT compressor contained a full 250 cc (which is sufficient for the entire system).

Based on logic, and without any personal experience, it appears that the mass flow of the refrigerant is too low. It's possible that the throttling valve is restricting the flow too much because it's somehow blocked. A pressure drop would also be present even with the throttling valve completely closed. The coolant flow seems to be only sufficient to cool a very small amount of fresh air. The temperature profile within the coolant circuit suggests that the blockage is not located elsewhere.

Hi,

I would try replacing the throttle body. If your compressor was faulty, there's a 100% chance that there are still metal shavings in the throttle body, and it also tends to get dirty over time.

I will have the refrigerant extracted again on Tuesday. I also think it's likely just the throttle valve. I will then clean it and, if necessary, replace it.

If it were truly clogged with debris from the defective compressor, wouldn't the system need to be cleaned?

Most likely, there are still more dirt particles remaining in the system, which could clog the restrictor again soon.

Does anyone know how to do this, and is it necessary to replace the dryer again when reopening the refrigerant circuit, or can it be done without replacing it?

Once, while I was at the workshop because of a faulty compressor, someone told me that the system could never be completely cleaned of debris, which would inevitably damage the new compressor as well. I was advised to have the entire system replaced.
I took that to heart and completely replaced or sold the car.

Based on your description, it seems the valve is the most likely culprit. Try removing it and cleaning or replacing it.

The dryer filter should only be left open for 10 minutes before being replaced. Replacements are available as accessories.

Regarding the chips. Before I would replace the entire system (which would be extremely expensive), I would try it like this one more time.

It was really the throttle valve!


Today, I had the system drained again, and then I removed the restrictor myself.

A cylindrical block of fused metal shavings appeared. It was completely solid! I tapped it a few times and tried to free the throttle from the material, but with no success.

I then cleaned the nozzles with cotton swabs and installed a new restrictor.

After another evacuation and refill of the system, the full cooling capacity was restored! (4°C from the ventilation outlet at maximum cooling capacity, with an outside temperature of 20°C).


Hopefully, this will last for a while.


P.S.: I didn't think the valve could be so tightly closed. However, it seems to have completely blocked the flow. Not a single drop made it into the low-pressure section.


THANK YOU VERY MUCH AGAIN FOR THE HELP FROM THIS FORUM!