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Found a 404a walk-in freezer with ice build up thru the evap to the fans. After de-icing, I found the compressor running during defrost cycle. The suction pressure stayed at (or about) 20psig and of course wouldn't go out on low pressure. I beleive the low/high pressure control is good. The unit is cooling great but I'm assuming the ice built up over a long time. Monday I'll really get to work on it (no overtime for me) and plan to check the soleniod(which did de-energize) and the compressor valves. How, exactly, is my question. The compressor, I plan on front seating valve at the receiver and watch my low side. The soleniod (I don't know), temp. difference? Any help would be great.
Last edited by Jevans; 01-09-2010 at 10:56 PM.
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unless its a hot gas defrost that compressor should not be running, thats the first thing to look at. does it only go into defrost on pressure. if your thinking that the ice build up is just over along period of time so it never thaws the coil out %100 then you may need to raise the psi setting for the cut in, on the pressure control
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Sorry, this is a freezer. It's pretty basic electric defrost by a timer. Defrost time set at 45min. 4x a day. When it's time(I advanced the timer) the fans stop, the soleniod de-energizes, and the compressor should go out on low pressure. It's also water cooled on a rack with 6(?) other coolers. All thier L/H pressure controls are set the same so I don't think I should re-adjust it (I did play alittle and it seemed to work correctly). Also, after playing with the L/H control I believe the defrost timer is okay.
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Does it have a defrost termination thermostat?
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Liquid or suction solenoid?
Use your gagues to diagnose a bad solenoid valve.
If it's on a rack then it won't 'pump down' like you are expecting.
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I didn't look at it but most likely it does, don't they all have a fan delay/defrost termination control? Let me add as an edit. Are you saying if the terminator is bad, it put it back into cooling right away, before it has time to pump down?
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Liquid, and my understanding of a "rack" may be wrong. It should pump down like others I've seen. It has it's own lines, I mean , it's on a rack sharing chilled water not 404a. What would my gauges say regaurding the valve seating properly.
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Yes, your understanding of "rack" is a lot different than mine. When you said it shared compressors, I assumed... OH well.
If the LLSV closed, then the pressure downstream of the valve will drop, obviously.
Temp will tell you most of the time if the llsv is bad, but I like to use my gauges to see those things whenever possible. A properly operating LLSV will also show a drop in temperature during pumpdown. It just won't last as long.
Either use gauges or take the valve apart if possible.
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Had my gauges on it and advanced it to defrost expecting low side to drop. No change in either readings at all, steady as a rock. So, I should measure temp on both sides of LLSV when it de-energizes and I should see a drop in temp? Also, are the compressor valves a possibility?Originally Posted by jpsmith1cm
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How long did the low side stay at 20?
A minute, 5, 10? This will depend on how long the lineset is.
The downstream side of the solenoid will get cold when it closes as the liquid boils off. If it's bleeding through, it will stay cold.
If you want to test the compressor, you can front seat the service valve and see it pump down. Best test would actually be to plot it's performance on the individual performance curve for that compressor. Suction, head, amperage and voltage and the curve will tell you if the compressor is good or not.
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I had my gauges on it for about 30min. Thank you for your reply's, I'll be going to bed now but look forward to any replies. Thanks.
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Sounds like your not pumping down, you found the coil iced up on arrival. Is there not a service valve in the liquid line at the rack?
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Yeah.
Look at that solenoid valve. Couldn't hurt to check the compressor, but I'd key in on the solenoid.
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Frigeguy-I hesitate now to use the term rack because what I'm seeing is simply a row of individual compressors sharing only chilled water. The only service valve I recall is at(after) the reciever.
jpsmith1cm-Thanks for the input. I'm studing this morn on how to work a performance curve for the compressor (can't recall going over that in school) but my gut is telling me it's the LLSV not seating.
Care to explain what your rack is?
HaHa, that didn't sound right.
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Yea the "king valve" close valve...watch suction, this will be a good test to determine if its liquid line solinoid or compressor.
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like they said , front seat the reciever king valve and see if it pumps down. If not do a performace curve or cheat if you have a suction service valve and front seat that and run the compressor into a slight vac and see if it holds. The performance curve is always the best way
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the coil is icing up. And remains that way, during and after defrost.
I can not see how you guys arrive at even the remote possibility the compressor is not pumping correctly. Ice means were removing heat. Means the compressor is doing the work. If the pump was not pumping we would not have ice.
I suspect you have a liquid line solenoid valve not shutting flow off. For what ever reason, and so the compressor will not pump down and shut off on low pressure switch.
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Multiple compressors pulling on shared loads.
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I had a similar situation about a month ago. The issue in this case was that the defrost time clock was not de-energizing the solenoid during defrost. Put your voltmeter on terminals 1 and 4 of the time clock during defrost; you should read voltage indicating an open circuit to the solenoid.
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The soleniod is de-energizing and the defrost timer acted good.
My real question was how do I know without question (if one could) the soleniod isn't seated? Seems after reading the replys, if it's failed completely and is wide open I should see no TD across it, and a partial seat would act like a restriction giving me a TD drop?
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