Wild AC problems

2000 Jetta TDI. So a few weeks ago I tried my ac in my new to me Jetta. The clutch wouldnt engage and the radiator fans wouldnt come on so I checked for low side pressure. I was a little low so I evacuated the system.

Then today rolls around... I pulled a 30 pound vacuum and it held for 30+ minutes. I go to charge the ac system and I only get about 8 oz of the 26 I needed to. The clutch still wouldnt come on and neither would the fans. I finally decided to check to see if my fans worked and discovered that only the high speed on the small fan worked. I ordered new fans because I'm going to need them anyway come full on summer. I also put power to the clutch and it engaged.

My question: will putting in the new fans fix them not coming on or am I looking at replacing a fan control module and an ac pressure switch?

Thanks in advance - Max

UPDATE
I replaced both fans and the ac works fine now

Have you checked the high pressure switch on the line?

Well I looked at it... Its a 3 pin, what should I check for?

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Whether it is functional? I had one on my wife’s Tdi that had some corrosion on one of the pins and the ac wouldn’t engage. After I found this I just replaced that switch and it fired right up.

Can I check its functionality with a multimeter? Also non of the pins are corroded

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I believe that if that switch goes bad/faulty, the system automatically senses high pressure and shuts the system down, no matter what the pressure is.

Can I check if its bad somehow so should i just replace it if the fans dont solve the problem

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Maxg1850n said:

....... I go to charge the ac system and I only get about 8 oz of the 26 I needed to.

Click to expand...

If I'm understanding this correcdtly it looks like your saying it only has 8 oz in it. If that's the case then the Fan control module will probably see there isn't enough freon via the Pressure sensor (not a switch), and as a result not turn on the compresser. So you need to get a complete charge in there.

Are you using cans? Did they freeze up during filling?

I was using 12oz can that didnt freeze. The fcm was hanging and not on a mount so that could be bad too

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Maxg1850n said:

Can I check if its bad somehow so should i just replace it if the fans dont solve the problem

Click to expand...

FYI. Fans that don't run on low speed wont solve your AC problem, but you should certainly replace them.

How to check a sensor. Check the three wires. Check power, check ground, check signal return.

One wire is 12V power, coming from fuse #5.

One wire is ground. Check ground, by back probing (this means with the circuit on and working) and making sure there is no voltage on it, or use some type of test light to make sure it will handle amperage. I sometimes use a headlight bulb for this, but will always check for voltage on the ground as well.

check signal return. Signal return is a square wave output where pressure corresponds to pulse witdh on the square wave. There is a document floating around here that shows how to check it with a meter, but I've goofed around with that and its clear as mud, so I look at it with an oscilloscope.

Maxg1850n said:

I was using 12oz can that didnt freeze. The fcm was hanging and not on a mount so that could be bad too

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Click to expand...

The pressure sensor not only serves to inhibit compressor engagement at high pressure, it also inhibits compressor engagement at low pressure. So you'll need to get a complete charge in there before you move further.

Understand that freon "carries" the oil through the system, and if there is no freon and the compressor comes on the compressor will fail. So fan control module has logic in it to prevent compressor failure if freon is low.

So then how do I go about getting all 26 oz in if the compressor isnt on to suck it down?

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You can jump the switch or preferably take it to a shop.

You put the can in a bucket of hot water. Should be able to get most of the charge in that way with the pump off.

I dont have a scope but discovered that fuse number 5 was blown... Could this be the issue?

CoolAirVw said:

FYI. Fans that don't run on low speed wont solve your AC problem, but you should certainly replace them.

How to check a sensor. Check the three wires. Check power, check ground, check signal return.

One wire is 12V power, coming from fuse #5.

One wire is ground. Check ground, by back probing (this means with the circuit on and working) and making sure there is no voltage on it, or use some type of test light to make sure it will handle amperage. I sometimes use a headlight bulb for this, but will always check for voltage on the ground as well.

check signal return. Signal return is a square wave output where pressure corresponds to pulse witdh on the square wave. There is a document floating around here that shows how to check it with a meter, but I've goofed around with that and its clear as mud, so I look at it with an oscilloscope.

Click to expand...

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POWERSTROKE said:

You can jump the switch or preferably take it to a shop.

Click to expand...

Maybe on a 99 that has a switch, but later cars have a sensor. (read my post above). You cant "jump" the sensor, in any way I know of.

Maxg1850n said:

I dont have a scope but discovered that fuse number 5 was blown... Could this be the issue?


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Click to expand...

Put a fuse in it and see.

That will definitely make the AC inop, but whether you have other issues or not wont be known till you put a fuse in. Obviously you still need to get a full charge in it.

CoolAirVw said:

Put a fuse in it and see.

That will definitely make the AC inop, but whether you have other issues or not wont be known till you put a fuse in. Obviously you still need to get a full charge in it.

Click to expand...

Fuse 5 didnt fix it but I found a 14 page pdf that outlines pretty much any problem possible.

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Maxg1850n said:

Fuse 5 didnt fix it but I found a 14 page pdf that outlines pretty much any problem possible.
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Click to expand...

that's probably what I mentioned above.

I suppose if you cant get full charge in you could jumper the compressor on to do so. Don't forget to check the other fuses that relate to the AC.

I've seen a few of the switches on the dash fail. Does the AC light on the button come on when you push the button?

Look at the fuse block on top of the battery. There are three 30A fuses in the upper right corner. The fuse on the left is #S180. I have seen a few instances where this fuse will overheat without blowing and melt the plastic base, deforming the contacts.

I checked that and they all look good

1854sailor said:

Look at the fuse block on top of the battery. There are three 30A fuses in the upper right corner. The fuse on the left is #S180. I have seen a few instances where this fuse will overheat without blowing and melt the plastic base, deforming the contacts.

Click to expand...

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Update: I replaced both fans and now the clutch engages. All thats left to do is put the remaining 18ish ounces of r134 in

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