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Old May 26th, 2018, 11:46   #1
Maxg1850n
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Default More AC Problems

2000 jetta alh. So I just got done fixing my radiator fans and now my ac clutch engages. I go to fill it with r134 with the car running and ac one and the low side and high side both had the same pressure the whole time. I let it get up to 100 psi on both the low and high side and even with the engine at like 3500 rpm the high side wouldnt pressurize.

To me it seems like a bad ac compressor. When I recovered all the refrigerant I drew a vacuum and I know the system doesnt leak. Am I overlooking something small or is this a standard mk4 compressor failure? Thanks in advance - Max

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Old May 26th, 2018, 13:14   #2
tadawson
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Either it isn't really running, or, as noted, the compressor has failed. I would think that even a badly hurt compressor would produce some pressure differential . . . Is there any movement in any guage when you engage/stop to compressor?

If I may ask, what are you using to charge/measure? An AC manifold guage set? This may sound insulting (and if so, sorry . . .), but if so, any chance you have both valves open, effectively bypassing the compressor? Long shot, I know, but about all I can think of outside not running or failed . . .

(I assume that your AC comp has no metering valve, since it has a clutch . . . .)

- Tim

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Old May 26th, 2018, 13:25   #3
pdq import repair
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Expansion valve stuck open? Did it work before? Why did you evacuate and recover just to do the fans?
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Old May 26th, 2018, 13:31   #4
Maxg1850n
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Quote:
Originally Posted by pdq import repair View Post
Expansion valve stuck open? Did it work before? Why did you evacuate and recover just to do the fans?
Didn't work when I bought it. Evacuated the system and then learned that I had to have working fans to get the clutch it come on at all. Replaced the fans and now this.

Could you explain they expansion valve?

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Old May 26th, 2018, 16:40   #5
pdq import repair
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The expansion valve is the part that actually produces the cooling effect. It is a restriction or jet if you prefer in the freon high pressure line. The high pressure freon is let out slowly through the valve and expands which causes the freon to cool.



It is usually mounted on the evaporator hoses where they exit and enter the evaporator. It also causes the pressure differential you see in a/c systems as it restricts the high side and increases it's pressure to make the system work. If the expansion valve is stuck open the pressures would be equal both sides of the system.


They are fairly easy to get at and fairly cheap so if it is a wrong guess you might need a compressor after all, but I like to throw in an expansion valve first in case, and oftentimes as part of any a/c repair as they can get plugged easily or stuck open by small debris in the line.
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Old May 26th, 2018, 16:58   #6
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A closed expansion valve will not, however, prevent a pressure differential in the system - if anything it would ma,e it too high. An open expansion valve would tend to cause a lower differential, but the system would still take charge and cool somewhat. It's not like an expansion valve can fail in a way to dump all pressure - working or not, it's still a restriction, as is the evaporator.
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Old May 26th, 2018, 17:03   #7
Maxg1850n
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So are you saying that it could be the expansion valve?
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Originally Posted by tadawson View Post
A closed expansion valve will not, however, prevent a pressure differential in the system - if anything it would ma,e it too high. An open expansion valve would tend to cause a lower differential, but the system would still take charge and cool somewhat. It's not like an expansion valve can fail in a way to dump all pressure - working or not, it's still a restriction, as is the evaporator.
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Old May 26th, 2018, 18:33   #8
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By the way II would think it's your RCV located inside the compressor.if it fails the pressures will be close if not equal.you have to pull the head off the compressor but it can be done while it's still on the car. I

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Old May 26th, 2018, 19:10   #9
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Actually, assuming everything is working properly, you could remove the two fans and through them in a trash can and the AC Compressor will kick-in when the AC is turned ON.

There are hundreds and hundreds of VWs on the road with dead fans and the owners have no clue but their AC works just fine while on the move!........ no good at all sitting at a traffic light or in a drive-thru!

When installing R134a, beginning with a vacuum of 29 inches or more, the first can should go in under its on pressure. The next partial can will go in slow with the engine at idle up to 1500 RPMs. The system should hold 750 grams +50 (that should be on a sticker under the hood). A 12 ounce can of R134a is 340 grams. Thus, two cans plus about 15% of the 3rd can. There is a bit of leeway, plus or minus. And, high revs will cause the Refrigerant Control Valve to affect the variable displacement of the compressor to be less effective. In the following link, scroll down to "A Problem Commonly Encountered With Internally Controlled Variable Displacement Compressors (ICVDC)" and read about revving the engine > https://axleaddict.com/auto-repair/V...nt-Compressors

I noticed the Freon capacity of the 2012 Jetta (gasser) is 525grams +or- 25 grams. That's roughly a 10% swing.

Anyway, there is a possibility that the Refrigerant Control Valve (RCV) inside the AC Compressor is the culprit. I'm not fully schooled on how it works but have general knowledge of it's function and the variable displacement compressor.
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Old May 27th, 2018, 08:25   #10
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Anyway, there is a possibility that the Refrigerant Control Valve (RCV) inside the AC Compressor is the culprit. I'm not fully schooled on how it works but have general knowledge of it's function and the variable displacement compressor.[/QUOTE]

The mk4 jettas dont have variable displacement compressors


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Old May 27th, 2018, 08:37   #11
pdq import repair
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A 2000 Jetta is a simple compressor and expansion valve system. If the compressor clutch does engage it can only be one or the other.



The clutch is engaging, right?
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Old May 27th, 2018, 08:38   #12
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Yes 100%
Quote:
Originally Posted by pdq import repair View Post
A 2000 Jetta is a simple compressor and expansion valve system. If the compressor clutch does engage it can only be one or the other.



The clutch is engaging, right?
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Old May 27th, 2018, 20:37   #13
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But, the compressor does have a Refrigerant Control Valve .....

Sanden SD7H16

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Old May 27th, 2018, 20:49   #14
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And a clutch? I thought it was pretty much one or the other, but am not familiar with all the details on these older cars. If so, that would be a good place to start - pretty much all the other suggested issues would still read some pressure differential, and well as some cooling somewhere (frost on a line whatever . . .).

- Tim
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Old May 27th, 2018, 20:59   #15
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Looks like the parts from a MKIII variable displacement compressor.
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