what are symptoms of a bad expansion valve?

[WANT '71 280SEL]

I'm specifically referring to my W109. I know people often replace these when opening the system, but would indicate one being faulty? It cycles the compressor on and off too much?

Thanks,

David

[MAKDUFF3]

Originally Posted by WANT '71 280SEL

I'm specifically referring to my W109. I know people often replace these when opening the system, but would indicate one being faulty? It cycles the compressor on and off too much?

Thanks,

David

Some symptoms of a bad expansion valve could be too much "cool" or none no matter the position of the temp control. If you compressor is cycle rapidly or very often (every minute or two) i would more likely suspect that the system is low on refrigerant. what I would recommend is that you take it to a reliable shop and have them, assess how much refrigerant you have in the system to what is prescribed and have them draw a vacuum on the system to check if it leaks. if they find nothing I would have them put your original change back in with dye to that you can use the system and the leaks can be identified in a week or so when you return. just my .02

MikeD>

[lorainfurniture]

If the txv is stuck closed you will have super high pressure high side, and very low (even vacuum) pressure on the low side

If it is stuck open you will have low reading on the high side and abnormally high on the low side. You must have gauges to find out

[alabbasi]

He has none of those, but there may be moisture in the system which would cause premature freezing and result in the compressor cycling.

[lorainfurniture]

It is also possible there is not enough refrigerant in the system either.. You have to investigate further.

[alabbasi]

Nope, he's using ES12a and low side is over about 45psi and low side is about 210psi at about 100 degree outside temp.

[MAKDUFF3]

Originally Posted by alabbasi

Nope, he's using ES12a and low side is over about 45psi and low side is about 210psi at about 100 degree outside temp.

That is a good amount of High side pressure.

You two put a set of gauges on the car and that was the reading?

If so one thing you should do is pull the pass side underdash trim beneath the glove box and feel the Expansion valve if it is cool before the valve but not so much after the valve... it is likely that it is not functioning properly.

Again, with an older car and if the system is not used often the process for trouble shooting, really should be to pull a vacuum on the system to confirm a proper charge and if it does then I would hold the vacuum for about an hour if it does not loose vacuum and there is cold to the expansion valve but not after, I would recommend replacing the expansion valve and in that also the receiver dryer and a recharge with dye for later problem solving if there ever was an issue. MikeD>