reversing valve or bad compressor

[paul_h]

I always struggle with this, sometimes it's hard to decide the faulty component.
The fujitsu ducted inverter I went to today didn't cool.
test running showed SP high (1100kpa), HP low (1700kpa)
I would normally expect 800kpa SP and 2200kpa HP

I tried to pump the system down, as I normally pump it down and inspect the flares.
It wouldn't pump down, it got to 100kpa sp reasonably fast but stayed at 100 kpa for 5 min.
During this time HP dropped to 1450kpa (wouldn't expect it to drop so fast)
Discharge temp was only 25C, would expect it to rise if you were restricting refrigerant ie like how DT rises when a system is short of refrigerant)

Anyway when I opened the liquid valve again DT rose to 60C, r/v out ws 58, suction in and out the valve was 6C/6C, so there didn't seem to be a bad reversing valve in my opinion, so I condemned the compressor.


It could have been an undercharged system with incondensibles, but HP was low.
It could have been a reversing valve fault, but suction and discharge temperatures in and out were similar.
It could have been a compressor fault, SP high, HP low, failed to pump down.

Any thoughts?
reservations I have are it could be an overcharged system with something else wrong with it too.

I always struggle with these decisions, most of the choices I make aren't by any hard and fast rules, just opinion, as I never know exactly what the differences should be. Anyone got any opinion on the best practice to be definite about them?

[Argus]

.

It's best to establish if the compressor is pumping efficiently and holds its pressure for a reasonable amount of time after turning off.

A suction gauge with the suction valve fully closed (clockwise) will tell you this. You should see a decent pressure below atmospheric or a 'vacuum.'

If the compressor isn't pumping, the four way valve cannot move, becasue it is operated by pressure difference through a set of servo tubes.

The reversing valve is such a simple device it seldom goes wrong - after all it only has two moving parts.

.

[paul_h]

.

It's best to establish if the compressor is pumping efficiently and holds its pressure for a reasonable amount of time after turning off.

A suction gauge with the suction valve fully closed (clockwise) will tell you this. You should see a decent pressure below atmospheric or a 'vacuum.'

If the compressor isn't pumping, the four way valve cannot move, becasue it is operated by pressure difference through a set of servo tubes.

The reversing valve is such a simple device it seldom goes wrong - after all it only has two moving parts.

.On a split system you can't close off the suction port. Closing the suction service valve closes your access port from the compressor too. With the service valve closed you can only read evap pressure, not compressor pressure.
So your only test can be closing the liquid valve for a pump down, but that doesn't remove the r/v from the equation, as a leaking r/v causes the same symptoms.
Hence my problem, and maybe why I don't have anything definitive for testing it. I swear I learnt something in school about them, but that was probably the same as what you said, closing the suction port. Which of course doesn't help in modern domestic splits.
Even if I pumped down, capped the flare and kept the valve open, I can not isolate between the compressor and the r/v in a split sytem.

Thanks anyway.

Also you don't seem to have realized the amount of crap and moisture that goes into a field installed system. Reversing valves don't fail often, but when you add incompetance into the calculation, you see a fair few die. I've seen way more faulty compressors though, which is what swung me most in this decision after the facts.
But I've had a lot of faulty r/vs too. Anything from the guy at the factory welding it in doing a bad job, to the local plumber installing the unit and filling it with crap that blocks the ports.
For example, this unit had oil over the service valve, a burred flare, and the installers have recharged it with r410a a few weeks after install. The flare is still crap, so the system most likely didn't ever get a decent vacuum. It's a ducted system going through two roof spaces, so most likely has weld joints that were done without nitrogen, the list goes on.
But I se your point about r/v reliability, for example through the wall one piece RACs never had r/v problems because they were done in clean conditions in a factory.
But split systems here are installed here by plumbers, electricians, labourers and fly by nighters, can't rule out a r/v fault, and like I said, no sure way to test it as you can't isolate the valve from the compressor

[1torr]

There should be another suction schraeder port inside the outdoor on the suction somewhere.

[philjd26]

hi paul,
i would say your right by saying the compressor is at fault, who knows what beaut charged that machine...way overcharged,liquid going back to compressor..gud night!

disconnect condenser fans and close liquid service valve for a bit and raise the head pressure if you can, shut the machine off and you might even be able to hear hissing noise coming from the rv....whilst checking temp. lets know how you get on.

rgrds phil

[AcidSlasher]

could the discharge service valve possibly be leaking? that would explain why it wont pump down, it could be letting some gas out into the system from the discharge valve and because its a small leak it would explain why the unit seemed not pump down.




now that i re-read the question again im going for the compressor. :P

[brianubaldo]

hi paul


I always struggle with this, sometimes it's hard to decide the faulty component.
The fujitsu ducted inverter I went to today didn't cool.
test running showed SP high (1100kpa), HP low (1700kpa)
I would normally expect 800kpa SP and 2200kpa HP



suction pressure high and discharge pressure low is suspect of compressor defect. (loose compression)

_____________________________________________
brian
SAMSUNG Tech. Support