dual pressure control
i was doing a pm. found walk in freezer condenser blowing cool air. long story short unit reached temp. but the low pressure control was not opening allowing the contactor to de energize. its running -20psig. so i shut down the unit. allow my solenoid valve to reopen allowing my pressure to raise. i noticed alot of oil running out at the connection. someone brazed on a gage port on the suction line about 6'' away from the comp. at about 5 o'clock spot. after leaving the job im thinking what happened was the line filled with oil so the control couldn't sense the pressure properly. i know sometimes they get stuck closed and you knock on them and it will open but i hit it pretty good but she stayed running. after installing the new one it ran for about 20 minutes before reaching temp again and it went to about -5psig then cut out when it was set for 0psig. any input
are you using your manifold to adjust the pressure? Or are you using the scale on the pressure switch? I have yet to find a scale that is accurate.
You may wanna get that fixed asap. Letting your compressor run in a vac will draw in noncondensables and other nasties if you have a leak in the evap. Also very bad for the compressor.
Last edited by vzenuh; 03-27-2012 at 08:50 PM.
Reason: re read what I wrote and noticed I missed some words, plus I reread his post and wanted to correct some other things that I
You need to set them with you're manifold. And yes they get oil in them and don't work properly. Try to install the flare fitting verticly if possible. If you have to install it horizontaly, bend the 1/4" end up if you can.
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i should have also stated. i raised it up to about 5psig and it cuts out at 1 or 0 psig. which is ok.
yes i watch my gage manifold to see where it actually cuts in and out at. i feel the old control was still good just pressure sensing line was filled with oil since the control was lower than the connection.
i bent it up but now basically it has a mini trap that will hold oil. ill check back on it. if anything ill put on a t and go off the gage port. but i try not to use them ive snapped enough of them
I'm not entirely sure that I buy the oil clogging the sensing line theory.
I'm not seeing it, guys.
Make me understand it.
I'd suggest replacement. That control is junk.
Oil wont affect a presure control. Even if you have a column of oil in the dual presure control the oil is still being pushed by the presure in the circuit. I always adjust them with my manifold.
The control is new. You are trying to set with no differential. It is also true we don't want to run in a vaccume at any time. Install suction port in a vertical position on the suction line preferably at a high point. Try a setting around 15 cut in and 4 cut out...depending on the gas your useing which is not mentioned, this should work. At your setting you are not applying any spring pressure on the differential adjustment . Ive seen this setting used to hide other problems such as a plugged txv screen, plugged liquid dryer, or improper superheat setting (too low).
Originally Posted by jpsmith1cm
Just watch your gauges and set the cut in and out. A sticking low pressure control is a sure way to lose those compressor valves
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