So I was in a traffic jam moving slowly when I hear a loud bang and saw mist coming out from the engine and the AC immediately ceased cooling.

I went to the garage and they told me an overpressure occured and I need to buy a new high/low pressure switch and diagnose the system

My question is, why would an electrical fail at all in one random moment, and especially why is it connected to the rest of the AC pipeline.

attached is a photo of the damage. Should I inspect or replace something else while I'm waiting for the part?

33 minutes ago, PIXIP said:

My question is, why would an electrical fail at all in one random moment, and especially why is it connected to the rest of the AC pipeline.

For a pressure switch to function, it must be in contact in some way with the fluid whose pressure it is reacting to. This means that if the pressure is high enough, or the part in contact is weaker than it should be, or has a seal failure, the refrigerant will escape when the pressure switch fails. 

 

It may look something slightly like this in general terms:

How a Pressure Switch Works ~ Learning Instrumentation And Control Engineering (instrumentationtoolbox.com)

Edited 12 July, 20233 yr by Pete1

What i can tell you is that you can turn that switch out of that dryer cardridge without opening the AC system. There is a valve in the dryer, so turn the switch out quick, for a short moment it will blow out some of the R134a, dont breath it in !!!

 

I have build in a lot of OEM ACs in 6N Polos and i always used to coat the O-Rings with AC Oil before mounting them. Just an advise.

 

My fault two years ago was that expansion-valve was faulty, i changed it and i used all four O-Rings new, coated them all with AC Oil before i put everything together. Back then the AC System was open, so refill costs a lot, also that new dryer with that pressure switch. So i hope for you just the switch was faulty.

 

plz give us feedback what it was in the end.

Edited 12 July, 20233 yr by Christian6N

Thank you both for the information! Should I try to replace just the switch as a first step? Is there a way to test the system with gas after I replace it?

i would change it at first, then you see if the ac is still working or maybe empty cos of that incident.

Maybe that switch was just faulty, or as i always use to think about..... this parts, in case it is original, is at least 24 years old or older cos the 6N1 was made untill 1999. so that can always happen to such old parts. even when its so very hot in the enginebay, especially in summer, in a traffic jam and with ac on.... 

 

When it wont work after that, u need an ac specialist...

But 1st give a new switch a chance.

i keep my fingers crossed for you.

 

cheers

 

Christian

Thank you! I already ordered the part.

And yes it's a 1999 Polo indeed. 

Unfortunately, I ordered an aftermarket part, and when trying to replace it noticed that the inner threads diameter is too small! it won't fit

In the photo the one on the left is the original broken one
 

any progress?

Yes! It was resolved successfully!

I ordered another part (a second replacement) from a Golf owner on eBay, but when it arrived I had trouble screwing it in without lifting up the vehicle.

After getting it to a AC mechanic, he was able to install it and ran a vacuum test on the system and filled it with a believe 500g of R134 refrigerant. 24 hours later and it still works great.  

Cool, but it shall go down to 6 or 7 degrees, 14 is not enough.

And the ac contents 750g of R134a, maybe thats the reason it brings "only" 14 degrees.

 

Oh good info! Does it depend on ambient temperature?

I'll swing by the agrage tomorrow and ask about the quantity 

15 hours ago, Christian6N said:

Cool, but it shall go down to 6 or 7 degrees, 14 is not enough.

And the ac contents 750g of R134a, maybe thats the reason it brings "only" 14 degrees.

 

Hi I wanted to thank you for that! I came back to the shop and they checked some technical literature where it says I need 720g. So they did a full recovery cycle and vacuum test and filled it up again. Looks even better now!

Sorry to dissapoint you, there indeed belong 750g into the system.

Both of my 6N1 have these stickers: