I am still learning about the controls on walk in freezers and coolers. I'm servicing one that is very old.
the evap sometimes freezes. I have been in my school books trying to understand the different types of controls.
I see how the pump down cycle works - shutting down the LL solenoid - pressure drops and contactor opens
via the low pressure switch. This unit has a defrost clock and a low pressure switch. the low pressure switch
has been by-passed. I don't have any info on the unit itself, It is 208/230 thee phase, single evap and condenser
the temp has been fluctuating between 20 & 30 deg, the label says 502 refrigerant. Sight glass is pretty clear. I'm just
not 100 percent sure what type of refrigerant is in it. I've been reading posts and I understand that if the door doesn't
seal properly, it can effect the temp. This one may have multiple problems. I have set 4 stops on the clock. the heaters
are working - I checked today. They get hot during defrost. Is it standard procedure to have a defrost
clock in conjunction with a LL solenoid > pump down circuit? I ohmed the contacts on the low pressure switch and
they do open and close when I adjust the cut out and cut in setpoints. but i'm not sure what to set it at, if I were to wire it back in.
Oh well i'm just trying to get some feedback. The defrost clock door will not shut and it is exposed to the weather. I should take some
pics on my new phone (Galaxy S4 Active) and repost tomorrow. this is quite a sight to see. When I say old, rusty and beat up - I mean
every word of it. thanks and sorry I don't have any model #'s tonight.
Its real common for the defrost timer to de-energize the liquid line solenoid and evaporator fans. This in turn will cause the compressor to pump down and shut off on the low pressure switch. At the same time the defrost timer will power the defrost heaters.
If the low pressure switch is bypassed - when the unit goes to pump down the compressor will just sit there and pull into a deep vacuum. That is very hard on the compressor.
Your box temp is 20-30, and its a freezer. Have you checked pressures, and superheat? Sight glass is pretty clear? Does that mean its bubbling? Is the coil froze?
How often does the evaporator freeze? Every couple days, every week?
I see you're a professional member. If you have the thread moved to Pro Forum - Refrigeration and Ice, we can get into a better technical discussion than in this open forum.
You might want to post a full set of numbers like superheat and outside air temperature. I had a freezer condenser running 502 in the heat of the summer would never keep up above 100 outside.
Could be that its been set up to not pump down and simply bangs the comp off and on on temp and defrost. This is a terrible way to run a freezer or cooler. A bypassed LP switch is never ever a good thing. The comp contactor should be controlled by pressure switches. The LLS should be controlled by temp control through the defrost timer.
I found a schematic. Very old I managed to piece it together and make a copy. It's pretty legible, but it does not show
the LL solenoid or indoor stat. I've seen some that have the indoor stat wired in series with the LL solenoid. Still not sure
how this one is wired. The gasket on the bottom of the door is gone - there is about 1/2 inch gap. Evap keeps freezing -
very heavy frost actually. I tinkered with the defrost stat. It is set to defrost 3 times a day - 30 minutes each. Outdoor temp
is 92. I talked with the man who used to service this. He said it has 404a he thinks. Head pressure is 350. Suction 50.
I don't have superheat. I will get it. I'm thinking it might be overcharged if it is 404. I need another day with it. Insided temp is
fluctuating between 20 & 40. I want to wire in low pressure switch. I'm not sure how to adjust cut in & cut out. Thinking about
replacing it with new one. I put in a new defrost stat on the evap coils - it didn't help. I got to get up at 4:30. I will check in
tomorrow.
when the defrost is active the fan motors should stop. check to see if the LLSV is leaking. if so replace it. also when the low pressure is by-passed that means the LLSV is leaking. look at the TXV and that will tell you what kind of refg that TXV is rated for. compressor model will also give you a clue. low temp usually takes all day on a new service call. if you had this account for awhile then their should be a record.
if you have a lot of traffic in that cooler with the door opening and closing you will have alot of frost build up. look at the traffic and when they are complaining. usually it is during the busy times
With a 50 pound suction pressure on any of the 502 "family" of refrigerants, you're only going to hold a 25 degree or so box.
WHY is the suction pressure so high? This is the first problem that you've got to address.
I would set the low pressure control to cut IN about 20 pounds and out just above 0. Do NOT rely on the printed scales on the control, but rather set it with an actual pressure source and an accurate gauge. Record the settings on the cover of the control. Make this a habit.
A superheat readings is just about useless at this point in time. Your box isn't even close to temp, so let's not get too worked up over that, YET. When you get it close to temp, then once you're SURE that you've got a solid column of liquid to the TEV, adjust the superheat.
Now, let's look at the icing issue.
You've tried 3 times a day and 4 times a day and neither are working. You've also replaced the termination control. Have you actually sat there and WATCHED the defrost? Stop fiddling with the timer and mark it BEFORE you touch the ****ed thing. Now, go have a coffee. Did the timer move? If not, change it. IF it moved, advance it to a defrost, put your coat on and go check the amperage of each defrost heater and write that down. Stay in there, monitoring the amperages until the defrost terminates. Why did it terminate? Is the termination accurate? Make adjustments or corrections as needed.
From the sounds of your post, you're flailing around. SLOW DOWN and THINK. This ain't rocket science, it's just a little applied physics. It's not all that difficult.
With a 50 pound suction pressure on any of the 502 "family" of refrigerants, you're only going to hold a 25 degree or so box.
WHY is the suction pressure so high? This is the first problem that you've got to address. THIS
I would set the low pressure control to cut IN about 20 pounds and out just above 0. Do NOT rely on the printed scales on the control, but rather set it with an actual pressure source and an accurate gauge. Record the settings on the cover of the control. Make this a habit.
A superheat readings is just about useless at this point in time. Your box isn't even close to temp, so let's not get too worked up over that, YET. When you get it close to temp, then once you're SURE that you've got a solid column of liquid to the TEV, adjust the superheat.
Now, let's look at the icing issue.
You've tried 3 times a day and 4 times a day and neither are working. You've also replaced the termination control. Have you actually sat there and WATCHED the defrost? Stop fiddling with the timer and mark it BEFORE you touch the ****ed thing. Now, go have a coffee. New guys, who are worth their weight, are not wired to have coffee. To busy trying to be the hero. Did the timer move? If not, change it. IF it moved, advance it to a defrost, put your coat on and go check the amperage of each defrost heater and write that down. Stay in there, monitoring the amperages until the defrost terminates. Why did it terminate? Is the termination accurate? Make adjustments or corrections as needed.
From the sounds of your post, you're flailing around. SLOW DOWN and THINK. This ain't rocket science, it's just a little applied physics. It's not all that difficult.
SLOW DOWN. Air infiltration should be the last thing you check before ALL other diagnosis' are exhausted. Now, go figure out why the suction pressure is so high. First thing I would start with is...wait for it................................................ ..................................
wash the condenser coil.
Local 597 Service Fitter
Metal Trade Journeyman
PAY ME NOW OR PAY ME LATER
It was working when I left...
Liberalism-Ideas so good they mandate them
definitely clean the condenser coil as far as the refrigerant, check the txv and see what it is designed for. it is likely 408a not 404a. as far as wiring its really simple. thermostat should be in series with the liquid line solenoid valve and defrost clock. then your lps should be set for 1-2 psi to accomodate for a little bit of drift on the compressor. also for the head pressure does it have a fan cycling switch? it may need to be set to keep liquid going to the txv instead of hot gas. check the defrost clock by marking it let it sit for about half an hour, go check something else then come back to it. evap fans and tstat and llsv should be on N.C. set of contacts on timer and defrost heaters on N.O. side. only after you take care of your controls and refrigeration problems should you look at air infiltraiton, but once you get to that fix the door gasket and make sure the drip pan drian has a trap on it.
Reply With Quote
Originally Posted by jpsmith1cm
