Strange Climate Problem: What's Happening?

Hello everyone,

I have the following problem with my Passat 3A5, AFN, 81 kW, TDI, with 105,000 km:
When I turn on the air conditioning, it cools normally for a short time; however, about 5 minutes later, it starts to get warm again (even though the air conditioning compressor is running).

According to climate specialists, there is enough gas present – the problem doesn't lie there.

Interestingly, the inlet pipe (which should be cold) is initially cold but later becomes lukewarm, while the outlet pipe (which should be warm) gradually becomes colder. Could it be that the compressor is somehow running 'in reverse' and circulating the refrigerant in the opposite direction?

P.S. While the climate specialists suspect the compressor, they are not entirely sure.

Greetings -sethmuc.

The compressor cannot run in reverse, and if it could, the motor would also run in reverse, as it is driven by a V-belt.

What does the error memory of the climate control system say? Have you had it read yet?

If the climate control system had a control unit, I would already have read it out (manually! unfortunately, it only has an on/off function).

Sure, I know it's impossible for the compressor to run in reverse (that's why I put it in quotes) - but that's how it seems to me, based on the symptoms.

Does anyone else have an idea? Has this kind of situation never happened before?

It's possible that either your evaporator is frozen, which is why the compressor isn't cooling (and is turned off), or the air conditioning system is overcharged, and after some time, the pressure relief switch will trip.

You can measure it again if the problem occurs again.

Hi.

Has anyone ever connected a pressure gauge setup and observed the pressure conditions at the moment of power loss?

Was the temperature measured to be overheating at that moment?

I could imagine that there is moisture in the system, which freezes in the electric valve and thus clogs the entire system.

In this case, the solution would be to empty the system, install a new dryer, evacuate it with nitrogen (1 bar overpressure), flush it, evacuate it again, and then fill it.

Best regards, Rüdi.

bastion wrote:

It is possible that either your evaporator is frozen, which is why the compressor is no longer cooling (and is switched off), or the air conditioning system is overfilled, and after some time, the pressure switch trips.

According to the original poster, the compressor is still running.

So, as I already mentioned, the compressor is still running.

During both the 'failure' and 'normal operation' phases, a service device was connected to both service ports. According to statements from two employees who operated the device (and who were from a radiator manufacturing company), this effect cannot be reproduced on the service device itself (meaning everything appears to be in order).
'Definitely, the compressor gets quite hot during operation (which is strange).'

Wouldn't a blockage be visible on the service unit? Or would the pressure relief valve not activate if there's a pressure buildup (and thus shut off the compressor)?

Hi.

In the case of a "blockage," the pressure doesn't increase, but the suction/evaporation pressure decreases until the normally-open (NO) switch is triggered.

How can you determine if there is enough refrigerant in the system?

Was it sucked in, weighed again, and then refilled?

Please provide some information.


Best regards, Rüdi.

Sure, @Rüdi.
It was extracted and then reintroduced (and, incidentally, it was discovered that only about 100 grams were missing from the original 750 grams after a few years).

Okay, I had imagined the blockage similarly to a throttle – it's clear that the pressure decreases at the back because the pump (compressor) can't pump as much as it could . That would also explain the hot compressor.

So, I inquired again with the people who took those measurements.

'There should be constant pressure within the system, maintained by the running compressor. If there were a blockage, a pressure fluctuation would have been detectable (especially concerning a full dryer). The compressor is supposed to always provide a pressure difference of approximately 2 bar, meaning it should always fluctuate slightly. In my case, the problem is that there is constant pressure in the system, so the compressor isn't actually doing much, even though it's rotating.'

What do you think about it?

Hi.

There must be a pressure difference; otherwise, the compressor will be faulty.

Are you sure that the magnetic clutch was always engaged during the downtime?

Best regards, Rüdi.

So, that guy was certain, and I couldn't detect any 'clacking' or difference in engine speed. Also, the fans were still running, which they usually turn off even when the AC is inactive. And the magnetic clutch is basically the 'main switch,' as far as I can see.

I'm getting increasingly frustrated with this issue. Yesterday, I tried to reproduce the problem again and wanted to check the wiring by 'touch' and verify the compressor activity. To do this, I initially drove around outside because the car is parked in an underground garage with a temperature of about 14-15°C. I wanted a car that had been heated by the sun, rather than creating an illusion of a properly functioning air conditioning system due to the cool air supply.
Interestingly, the cooling system was working - although the performance varied from excellent to weak (subjectively felt) - it was still present.
As expected, the thinner pipe (HD pipe) was cold, while the thicker pipe (ND pipe) was not. And it wasn't just a little cold; it was extremely cold. That's certainly strange.

If the thin high-pressure line feels icy cold, there must be a restriction or blockage somewhere. Continue feeling along the line in the direction opposite to the refrigerant flow until you find a warm spot; there should be a narrowing or blockage there.

Starting from the compressor, the high-pressure line goes to the condenser. This heat is blown away by the fan. After the condenser, the temperature should be from outside temperature to lukewarm. To the right of the dome cover, towards the water tank, there is a threaded connection where the expansion valve is located. After this connection, it should feel very cold. From there, the low-pressure side leads into the interior to the evaporator. After the evaporator, the thicker low-pressure line should still feel cold. This line leads to the dryer located under the right bumper, and then back to the compressor. Good luck finding the problem!

T3Surfer wrote:

If the thin high-pressure line feels ice cold, there must be a bottleneck or blockage somewhere. Continue feeling along the line in the direction opposite the cooling circuit until you find a warm spot; there should be a constriction or blockage there! Coming from the compressor, the high-pressure line goes to the condenser. This heat is blown away by the fan. After the condenser, the temperature should be from outside temperature to lukewarm. To the right of the dome cover, towards the water tank, there is a threaded connection where the THROTTLE VALVE is located. After this connection, it should feel ice cold! From there, the low-pressure side leads into the interior to the evaporator! After the evaporator, the thicker line should still feel cold. This line leads to the dryer located under the right bumper, and then back to the compressor. Good luck finding the problem!

Your description is appreciated, but it's incorrect!

Coming from the compressor is the so-called hot gas line, which, as the name suggests, must be very hot. This line goes to the top of the condenser (also known as the evaporator). From there, the so-called liquid line runs down to the dryer (which should be slightly warm to the touch), and then from there, through the expansion valve (electronic valve) to the evaporator. At the evaporator, the refrigerant experiences a pressure drop and evaporates, and then it flows back to the compressor through the so-called suction line.

If the (thin) refrigerant line is already cold before the expansion valve, it indicates a blockage. Most likely, the dryer is the culprit. Restart the system and then check the dryer again. If the dryer is cold, the problem is likely located there.

With a magnetic coupling, you might not necessarily hear a "click." You need to check if the inner part is rotating with the outer part. If only the pulley is rotating, then the compressor has likely been shut off, which would make sense. In the event of a blockage, the ND switch would shut down the entire system.

The dryer is located on the right front side, behind the bumper, directly next to the horn. You can reach it from underneath.

Best regards, Rüdi.

Thanks for the tip - I'll inspect the entire system again.

I'd also like to add that it seems these 'climate experts' aren't really experts – they were talking about 750g of R134a, while, amusingly, the repair manual specifies 1150 (1200)g, depending on the compressor model.

sethmuc wrote:

I'd like to add that apparently, the so-called "climate experts" aren't really experts - they mentioned 750g of R134a, while, amusingly, the repair manual specifies 1150 (1200)g, depending on the compressor model.

The exact filling weight is 1150g ± 50g.

"Rüdi, In the Passat, the air conditioning system uses a throttling system, where the dryer is located on the low-pressure (LP) side. In the Golf, for example, it uses an expansion valve system, where the dryer is located on the high-pressure (HP) side. These are the differences. In older Passat 35I models with the transversely mounted engine, it's an expansion valve system. In the 3B Passat with the inline engine, it's a throttling system."