A/C hi/lo pressure switch went bang!!

[tooarbie]

Anyone have a good understanding of the Air Con a T4 Caravelle?

Hit a kangaroo (that's life in Oz) and ended up have a bunch of panel work to the nose and a new radiator and A/C condenser. Following the repair I noted a chattering that turned out to be coming from the hi/lo pressure switch. Before it exploded. After replacing this switch and regassing it was noted that the fans were not switching on in response to either the A/C being switched on, or increasing engine temperature (obstructed airflow through radiator also confirmed integrity of radiator fan switch)
Long and complicated story. (Mis??)diagnosed as a faulty fan relay. Different VW specialist identified and replaced failed/damaged fan resistor/s. All good now ... albeit via an expensive failure of the rear evaporator unit. Over $1000 after regassing ... ouch!!

I'm struggling to understand how the system was unable to protect itself when the fans failed. Pressure seems to have gone ridiculously high, destroying the hi/lo pressure switch (it exploded) and I'm wondering if it may also have contributed to the leak in the rear. How and where does the pressure build? And why didn't the hi/lo pressure switch stop it?

I want to put a case to my insurer that the whole lot is their baby! If I can't find a satisfactory explanation to the contrary.

Thanks !!


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[LogicprObe]

I'm guessing they replaced the big fuses near the battery.
That's what was gone when my fans didn't go.
It's usually a sign one of the fans is on the way out.

[tooarbie]

I'm guessing they replaced the big fuses near the battery.
That's what was gone when my fans didn't go.
It's usually a sign one of the fans is on the way out.

Fuses were all intact. It was the big resistors mounted under the radiator. There are two of them. They appear to be wound around a ceramic core. You only get to see them with the sump guard off. Any way replacing them got everything working again.

But I kinda suspect that the A/C pressure going high damaged my rear condenser and caused it to leak.

After the repair it was only about two weeks and it stopped working. Of course repairer wasn't interested in my hypothesis. They only worked on the front of the vehicle. It was a front-end collision. The rear A/C evaporator is in the ... rear!

I just would like to be able to understand how the A/C is controlled in the T4 Caravelle.

And more to the point, how does it protect itself should the condenser stop condensing eg because the fans are not operating.

In my situation a new hi/lo pressure switch (the one that is mounted on the receiver/drier) was replaced. The technician at the panel shop that did the original repair gassed it up but the pressure was going too high, so he sucked the gas back out, and threw his hands in the air!!

What was concluded was that the hi/lo pressure switch going bang, (and it really blew apart!!) rather than being the cause of the problem was actually a symptom.

Mmmmm ...


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[Syncrotek]

Always helps to have some info about - What year model ? what sales no. ? what engine & code ?(i.e. AES, ACU), manual or climatronic system ? build codes help too sometimes.

BTW - this all assuming original equip. not aftermarket system.

I'm not real familiar with T4 system, but they are similar to others - The A/c safeguards are the fuse (elect circuit), temp cut-out switches, pressure cut-out sw., and an over-pressure relief plug on the compressor. The controls differ on the manual and climatronic systems, but the basics are - A/C sw >> E33 evap temp. sw >> F129 Press sw >>F163 Temp cutout sw >>J365 A/C switch off (Main) Relay >> (maybe not in the exact order) The a/c temp. and radiator temp switch is a combined unit.
No condenser at the rear, and the evaporator is on the low pressure side of the system. Without knowing what the diagnosis for the rear problem was, one can only speculate, but rear systems are known for leaking, - blanking plugs are available for rear system pipes.
Have seen this trouble when the pressure switch has been bypassed for testing purposes, and forgotten to reconnect, therefore high pressure has no shut-down control.