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MILLWALL
28-09-2007, 03:55 PM
Hi new to ac etc. Got a unit that when running pulls down a vaccum on the suction side and after the expansion valve. I know there is gas before the valve. I think the expansion valve is faulty. Am i right.

davej
28-09-2007, 04:23 PM
HI welcome to the forum, im not sure i would say the valve is faulty more likely it is blocked.
you need to maybe carefully warm the vale (hot water) and if it is moisture you will hear the gas start to pass. if that is the case then reclaim the gas and remove the valve certainly clean, probably replace valve and orrafice. change drier and vac well. then recharge

monkey spanners
28-09-2007, 04:31 PM
Is it an air con unit? I've had blocked strainers on R22 ac before. I've not had an problems with inveter systems yet with the electronic expansion valves so can't comment, but would think you would need to rule out an electronic/electrical problem to the valves stepper motor before thinking of a mechanicl/physical restriction.
Is it a refrigeration system? Does it stay on a vacuum when you shut the compressor off (you may need to shut the discharge valve to rule out a leaky valve plate etc) If it does it could well be the valve. Does it rise after a while? could be moisture (what does the sightglass show?) or still a duff valve.
Could also be a blocked drier, a faulty solenoid coil, damaged liquidline pipework, system could be pumping air if its had a leak, this will give a high headpressure and a vacuum.
What type system is it? Size? Refrigerant? Any history? How do you know its got a vacuum after the valve and gas before?

Oh and hi, welcome to the forum Millwall

Jon

frank
28-09-2007, 04:36 PM
Is the liquid line stop valve open??

monkey spanners
28-09-2007, 04:40 PM
You wait half an hour the three come along at once.....

MILLWALL
28-09-2007, 05:11 PM
It is an ac system, denco downflow. Liquid before the valve seen via sight glass. Shrader point after valve before enters coil. Has had a leak before which has been repaired so i'm told????. Drier has been changed, sight glass showing full. Liquid line stop valve is open.

Cheers for all the help so far guys.

monkey spanners
28-09-2007, 05:27 PM
Sounds like its new valve time then. If its a danfoss or teddington valve the orifice/strainer in the inlet show be sprung (you can push it into the valve by 1-2 mm) when the liquid line is removed. If not the phial/bellows has lost its charge (capiliary rubbed through?) this will cause the valve to shut completely and give the symptoms you have given.
Dry the connections to the valve to prevent any moisture getting in when changing it. also fit a new drier. pressure leak test. vac out. fingers crossed. see if it works.
I was thinking more of moistue when i said sight glass, i should have been clearer, is the indicator green,blue (dry) yellow,pink (wet)

Jon

MILLWALL
28-09-2007, 05:32 PM
Cheers Jon will order new valve and see how its goes.
Once again thank you all for your help.

Andy AC
28-09-2007, 07:13 PM
I've had the capilary rub through on denco units before so definiteley worth checking. We've got one gone down at the moment with the same symptoms as yours, but they are reluctant for us to investigate further.

Andy