MK4 Air Conditioning Recharge?

[vasillalov]

Hi all,
I own a 1999.5 MK4 Jetta GL. I am begining to think that the air conditioning system needs to be recharged. There are no leaks as far as I know because the AC works as it blows cool air and dehumidifies the air.

The Bentley sais that when the AC is engaged with the fan on 4 and the engine running @ 1500 rpms, then the temperature should drop to 10 degrees Celcius at the dashboard vents WITHIN 1 MINUTE!

In my case this does not happen at all. While cool air indeed starts to blow, it might take it good 10 minutes of operation for the air to be well chilled.

This makes me think that my AC system needs to be recharged.

Now the Bentley also sais that our AC systems require R134a refrigerant AND some synthetic AC compressor oil. This is my primary concern! I know I can recharge my AC at any AC shop since but what about this compressor oil?

Is it the same as the engine coolant (G12): don't mix it with the one for american cars? Or is it designed to meet certain environment standards and it is interchangeable with any compressor oil?

Any thoughts and knowledge will be greatly appreciated!

[digitalhippie]

Here's the issue. Over time, air/moisture do make their way into the A/C system. So even if you don't have an outright leak, contaminants have probably made their way into the system. Just recharging it isn't enough... in fact, your pressure levels are probably ok. The system needs to be purged (with nitrogen) then completely refilled with R134a (which usually comes with the oil in it, its just a standard AC compressor lube, nothing special about it).

[vasillalov]

Quote, originally posted by digitalhippie »

Here's the issue. Over time, air/moisture do make their way into the A/C system. So even if you don't have an outright leak, contaminants have probably made their way into the system. Just recharging it isn't enough... in fact, your pressure levels are probably ok. The system needs to be purged (with nitrogen) then completely refilled with R134a (which usually comes with the oil in it, its just a standard AC compressor lube, nothing special about it).

Yes I was assuming that this is the case since I don't think that there are any leaks whatsoever. So basically, any Auto AC shop can purge the system with nitrogen (as also directed in the Bentley) and then charge the whole system?

Well here is what the Bentley sais about R134a and the compressor oil:

Refrigrant capacities depending on AC Compressor brand:

Lubricant capacities depending on AC compressor brand:

The fact that the Bentley speciffically shows a lubricant part number, makes me think that the AC oil is VW/AUDI speciffic and should not be mixed with other AC oils.

[BORA 18T]

You have to remmember that the ambient temperatures (outdoor temp.) has a large effect on that 10 celcius. If it's 90 degrees in one car and 70 degrees out in another car the supply air temp coming out of the vents will be different. The pressures will run differently and everything due to temp changes. Usually a standard AC system will run at about 18-22 degree temp difference from the average temp in the space to the supply air temp. If you have refrigerant in the system then there is no way that air or moisture will get in there period. Note... As long as no one has ever messed around with your AC system. All the refrigerant would have to leak out for the air and moisture to enter. air and moisture isn't the problem. If you can find the condenser coil outside the car, I would take a look at that to make sure it's clean. If it's dirty then that will effect the performance of the AC. A good way to kinda see if the AC is working good without checking pressures is to run the AC (as long as it's like 70+ outside)
and see if you end up with water on the floor underneath the car. I wouldn't worry about the oil in the system unless you have a leak. in which most cases you just need to add refrigerant and not oil because most of the oil stays with the compressor. only some migrates thru the system. If you have any more questions IM me and I can help you out. I know about this stuff because I do it for a living. I'm a heating and AC service technician.

[digitalhippie]

That's funny, I actually have a background in HVAC systems too... and the way I learned it, rubber fittings leak. Rubber is permeable. Air/moisture make their way into the hydraulic brake system for the same reason they make it into the A/C.

But hey, that's my $0.02

I know on my 01, it needed to be purged and refilled last summer. The A/C system's perfomance had faded (as Vasil described). Condenser coil was getting proper airflow, so that wasn't the issue. The system was checked for leaks (using UV die) and none were found.

Also, Vasil... the PAG oil is the same. VW has a part number because they sell you the "vw stuff" when you bring it to them for a recharge.


Modified by digitalhippie at 12:07 PM 5-22-2005

[vasillalov]

BORA 18T,
Interesting info..

About the water solubility (From The Bentley):

I am sure you are aware that the AC system works by converting liquid to gas and back in order to achieve thermal transfer. So an AC system in fact can absorb a lot of moisture for as long as the leak is in the low pressure part (the one with the gas).

So the refrigerant oil is the same for all R134a systems including the ones for VW, correct? Also, what brand of R134a do you recommend? I plan on purchasing my own R134a and taking it to a shop just to get the system tested, purged and charged...

Thanks for your input!

[digitalhippie]

National Refrigerants always worked for me

[BORA 18T]

Yes I see your guys points but you have to remmember that in the case of R134a it is running in a positive pressure. Even the suction pressure is well above atmospheric pressure which is 14.7psia at sea level. The suction side is the low pressure vapor side. If there is a leak in a rubber seal or a leak of any sort, the refrigerant will leak out due to the higher pressure than atmosphere. In certain cases where It's a low temp application it's possible for 134a to run in a vacuum where atmospheric pressure is greater than the system pressure in which then the refrigerant will suck in the moisture into the system. My final thought ... yes it's possible for refrigerant to absorb moisture but thats only under certain circumstances where in the case stated above or if someone introduced it into the system. as far as the oil I don't know if it's the same for ac systems as for vw. vw does some weird stuff. to be honest I'm not aware of vehicle ac compressors oil types. I wouldn't worry about the brand of 134a. They all have the same chemical makeup. as long as it's virgin refrigerant i don't think it matters. On a side note no matter what you do there will always be moisture in a system. It just makes a difference when theres alot. the measurement is microns. To totally remove moisure from a system you would have to achieve a perfect vacuum. this isn't possible. therefore the allowable level of moisture in the ac field is 500 microns or less to be safe.


Modified by BORA 18T at 7:36 PM 5-22-2005