A.C. Expansion Valve ???
 

Have another post going about my A/C not working (compressor works fine, no cold air)

Has anyone had an expansion valve go bad causing their A/C to not work???

After replacing the compressor(just to make sure)
the Drier
making sure there are no codes in climate control system
seems like the expansion valve is the next thing to try...so have on on order (only 4 left in the U.S.)

Lucky for me son is Subaru Tech, so labor will be in Beer....would not want to have to pay for all these "trys"

Scott
Omaha

The expansion valve (orafice tube) controls the flow of refrigerant. If it's not working then the compressor would not go on. Did you check the surface of the condensor and the radiator? Kinks in hoses? Leaks? Drive belt tension? The blower motor and Fans? Why don't you go to a certified automotive A/C technician rather than changing parts at random? It may be cheaper in the long run.

The expansion valve doesn't control compressor operation.

Expansion valves and orifice tubes perform the same function but operate quite differently. A system can have one or the other but not both.

Expansion valves move either .007" or .016" - I forget - and can bind/clog quite easily. Plus, they operate by the pressure of a mercury-bulb/diaphragm which can also easily give up.

I don't recall all of your issues but a grenaded compressor may have sent particles throughout the system. The first place they collect is in the condensor, many times ruining it with clogs and restrictions. Ditto for the rec/drier. The garbage can go beyond that and plug the expansion valve (TXV) or orifice tube (as implemented.) The bad part is, even properly flushing the system won't always (read: almost never) remove the particles. It's even possible that a lot of the garbage can contaminate the oil and return to the compressor and ruin it, again and again.

So...remove the TXV and check it for particles. Even if you don't see any, and you suspect that the system may be contaminated with particles, flush the system, install a couple in-line filters to save yourself the anguish of repeat repairs.

Newer cars with 134 systems many times require a new condensor and rec/drier when a compressor fails because of contamination. The finely ground aluminum contaminates the oil and creates what is known as 'black death'. R134a requires high-efficiency condensors and as such they have very small and tight tubes and bends that easily clog from contamination.

Beav, I did not imply that the expansion valve controls the compressor, just the flow of refrigerant. If the expansion valve doesn't work, then no refrigerant will flow to the compressor. How can the compressor engage without any refrigerant going to it? :confused:

Like I said, A/C compressor works fine, line (pressure) gets cold for about 6-8 inches from the compressor back....yet no cold air. Work is being done at Subaru Dealership by my son who is a Subaru mechanic there. When we bought the car, A/C didn't really blow cold at all, so changed over to 134A. Never blew cold, yet systems work fine. It acts like a pressure problem.

Based on my experience on HVAC, if all is working fine, either your evaporator or condensor is not doing it's job. Sometimes it's just a matter of cleaning them.

Yes, its puzzleing. Even when I first got car (when it had R12) would blow cool...but not cold, untill finally it quit blowing even cool. I thought maybe it was just low on refrigerent, so decided to make the change to 134A. System took it fine but never did blow cold. everything seems to point to some restriction or lack of proper pressure. (high side pressure reads low....low side reads on the high side) based on the shop manual it says compressor is at fault, so found a good used compressor and had it installed......with no luck. His side pressure line was removed and checked for a blockage, but was clear.
will keep posted on progress.

Hi side low & low side high can also be a flooding TXV - no restriction, nothing to suck or blow against and cause a pressure differentiation.

The TXV has absolutely nothing to do with the compressor 'going on', flow has nothing to do with the compressor 'engaging'. However there are pressure switches that can prevent the compressor from cycling when the pressures are too high or too low. Some systems have a evaporator temp switch that will shut the compressor off to prevent evaporator freeze-up. The TXV does none of these things.

No big deal, I was just trying to provide clarity.

Our first Legacy had been converted to R134, from R12, and it didn't work when we got it, it ended up being the Expansion valve, had to take the dash out to get to it.....but after installing a new expansion valve, it worked great...

I'm in the same predicament with my new SVX, and expect it will be the same deal, so I'm just living without AC right now, as I removed all the AC stuff in FrankenWedge, and don't feel like pulling the dash out of my SVX right now (but I sure do wish the AC was working):rolleyes: Thinking about switching the cloth seats out of my parts car into it, so I won't be sitting on that hot leather:eek:

Huck, what a great looking SVX you have there! looks great in Yellow.

My SVX is Black, and its been in the 100's the past few days here so I don't want to drive it, although once you get going with all the windows down it stays comfortable.

Beav, if no refrigerant flows through the system because of a faulty expansion valve, wouldn't it cause high pressure on the high side and low pressure on the low side thus triggering the pressure switch and shutting the compressor from damage?

Thanks Scott, mine was a Ebony before I painted it...

Originally posted by Beav;(The TXV has absolutely nothing to do with the compressor 'going on', flow has nothing to do with the compressor 'engaging'.)

Here is some information I found about the types of auto expansion valves.

Receiver Drier (Filter Drier) - Expansion Valve System
This is the earliest and I think the best system. This system uses an expansion valve to control refrigerant flow and cycles the compressor clutch to control evaporator temperature.
Accumulator - Orifice Tube System
This system uses a fixed orifice and an accumulator to control refrigerant flow and cycles the compressor clutch to control evaporator temperature.
Suction Throttling Valve System
This system is the most complicated. It uses an expansion valve to control refrigerant flow into the evaporator and a suction throttling valve to control refrigerant flow out of the evaporator. This system does not cycle the compressor clutch, rather it cycles the compressors suction to the evaporator.

You don't have to pull the dash apart...only the glove compartment.