Three questions:

What causes an expansion valve to fail?

What are the symptoms of a failed expansion valve?

How do you access it's connection point in the engine compartment - from above, or while on a lift from below?

TIA.

 

I've seen more compressors internally faulty than I've seen expansion valve problems. I've actually never replaced an expansion valve.

What are your symptoms and reasoning for the diagnostic.

 

Nick(?): Thanks for your interest. Several years ago my a/c wasn't as cold as it had been. I foolishly tried one of those refrigerant-in-a-cans and after I connected it and tried to charge the system there was a 'pffft' from the vicinity of the compressor. Since then there has been no cooling at all. Took it to the dealer who wanted $1,500 to replace the compressor and drier. Since OE compressors were going for $300 I declined the dealer offer and planned to do it myself.

I have gone without a/c since then, but am now (at 150K) in the midst of a general overhaul of many things in the engine compartment, including the a/c. Research suggests that compressor failure can damage the expansion valve. Your experience suggests otherwise. Hence my confusion.

If the valve were easily accessible I would simply replace it, but without a lift it seems nigh impossible to reach the engine compartment side of the firewall in order to disconnect the refrigerant lines from the valve.

I'm inclined to skip it and hope for the best, unless you or someone else advises otherwise.

Thanks.

 

Over charging will keep the compressor from running, but can also cause catastrophic compressor failure.

I would recommend finding a shop with a recovery system to recover (if anything is in the system) and put it under a vacuum to see if there are any leaks in the system. After that I would start with the system being precisely charged with an AC machine, you never get the weight right when you try to use the can and either end up under or over charged.

If the system still isn't operating properly with a correct charge, and has been deemed to not have any leaks I would look at the compressor as a culprit. If these cars used a FOT instead of an expansion valve I would check it first, but the expansion valves don't have problems in my experience.

 

I've always wondered about the RCV (refrigerant control valve) on these cars. I know they were a problem with some MKIV Volkswagen platforms that had either lacking cooling or loss of cooling. There are a few write ups on how to clean and or replace the RCV, which seems about the same across the board for compressors. The valve is usually available for purchase and is quite a bit cheaper than a compressor, and if that turns out to be a potential fix it could start saving some people money!

Here is a link to some light reading on the RCV: http://www.aircondition.com/tech/que...-Control-Valve

Here is a link to a TDI forum that also shows some details on the RCV in the VW world: http://forums.tdiclub.com/showpost.p...06&postcount=5

If you're looking for a bit more info and pictures on the RCV click the link in the above thread and scroll to post 520 and there are some more in detail photos to be seen.

 

Thanks. I had the system evacuated and it held vacuum so I'm fairly certain there were no leaks. Since then I have completely removed the system, except for the afore-mentioned expansion valve. Once reassembled I will have it put under vacuum again and assuming no leaks, charged with an appropriate amount.

Next question: Do all qualified a/c shops know how much pag oil to introduce, and am I correct that it can be introduced after the system is otherwise completely reassembled?

 

There is literature that will tell you what the oil requirements are, but without removing the evaporator core, condenser, and compressor and totally draining them you'll never know how much is in the system.

You can introduce oil into the system after it has been fully assembled, but it is introduced during the charge procedure, and must be introduced into the high side of the system.