What is the best way to know if a expansion valve is shot ? compared to a reversing valve ? I know of tests for the reversing valve but none for the expansion vavle, thanks.. ... or restriction ?
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What is the best way to know if a expansion valve is shot ? compared to a reversing valve ? I know of tests for the reversing valve but none for the expansion vavle, thanks.. ... or restriction ?
if you have a restriction in the system u will have a pressure drop
Press/temp relationship means u can measure a temp drop accross restriction
Thanks. I know that I will be able to measure temp. and find the restriction but what if it's the expansion valve that may have the restriction ? How would you know for sure in that situation ?
If the txv has gone bad, it will either be over feeding or under feeding (very rare for it to be faulty and correct)
Make sure it is the correct valve for the refrigerant in the system!
First thing to check is for good air flow in the condenser and evaporator, clean filters, check the drier for temperature difference across the inlet and outlet, i have heard 2C being the max it should be but i think this is a bit high, again it depends on the system you are working on, it is good to take measurements from correctly working systems, that way you get a feel for whats normal and what isn't.
Once this has been checked and sorted, if the valve is under feeding i'd expect a lower suction pressure and a higher suction superheat and a lower head pressure and increased subcooling than would be expected in a properly operating system, how out of spec it is depends on the severity of the fault. This could be due to it having a restricted strainer or being blocked or stuck by water or wax.
You could try warming the valve with some warm water to see if it works and then apears to go bad again in time, maybe a few minutes or much longer, depends on lots of things.
Or it could have lost some or all of its charge in the phial/bulb, this will either make it run with too high a superheat or shut completely. (to be able to pump down the system to change the txv, you can cut the bulb capillary righ tight on the bellows and puff a bit of nitrogen in to open the valve with a gauge line held over the hole)
If its over feeding the first thing to check is the bulb, is it fitted correctly with a good contact to the suction line? Is it insulated and not getting heated by air from the fan or heat from the liquid line or other heat source?
The next thing to check is if someone or the superheat pixie (like the run cap bandit but smaller :D) has been at the adjuster, if they have set it back to factory possition and monitor the valve operation, if its still not right i'd fit a new one, much cheaper than a new compressor or high electricity bills from poor system efficiency.
For me its more a gut feeling that the valve ain't right, if i'm not happy i change them or the power element in the case of sporlan valves.
Jon :)
Thanks for the reply. I guess I find my self fighting bewteen a restriction at the valve or bad valve often, even at times wondering if the reversing valve is not all the way one way or another, I love this work, thanks again.. ...
I understand the suction side of things but how does that cause a lower head pressure? Would the extra refrigerant now on the high side cause a higher head pressure together with higher subcooling?Quote:
Originally Posted by monkey spanners
Funnily enough I came across the symptoms you describe yesterday. The Sporlan TEV had subcooled refrigerant of 11K but low suction pressure and high superheat. The power head was badly pitted so I concluded the phial charge had leaked out although the high side thing couldn't convince me completely. Going back on Monday with a new valve...
Cheers,
Andy.
Is it lower head pressure as less heat absorbed in the evaporator so less to reject in condensor - the system in a same state as if it was pumping down??
Quote:
Originally Posted by Tayters
Yeah, thats it! The only time i'd expect to see the head pressure rise with a partially shut txv is if the system is overcharged and liquid is backing up into the condenser.
Jon :)