Need some help on a walk in cooler nightmare
I am new to the forum this is my first post. I read most of the stickied and will try to follow the guidelines as much as possible.
Quick Background. I started work really with my dad when I was fourteen, he just retired so I took over the business, I'm 27 now. This is my first big refrigeration call Robert has helped some too (with this call especially) but he is admittedly stumped too.
To the call:
The cooler is mainly a drink cooler with some dairy and meat products it has about 8 glass doors on the front, and the seals aren't that great in my opinon.
The unit it self is a walk in cooler with two evaporator coils about a 40ft service line run and a Copeland compressor (R22) outside to a shack really with less than adequate ventilation. Last year in March I helped my father change out the compressor (he retired in April). Quick about things about the condenser no Manufacturing plate what so ever so unsure of manufacturing date or system specs i.e. Factory charge. We charge it with 9.5 pds. taking in the accumulator and long service line. Both of the service ports were run downs and leaked when opend so we put a piercing valve on the low pressure line. The running pressure was 32 on the low with a sat temp of 8. And the sat temp on the high was 60 (checked with the digimon Manifold, su[perheat peripheral). The temps out of the evaporator coils range 25-21. Thermostat set to 31-28.
I get the call two weeks ago that the evaporator is frozen, so I went to check it out and one of the condensing fan motors was out so I replaced it and frosted the coil.
Got the call last week that it was freezing again so I figured fre-on. I checked the pressure on the low and it was 8psi. I defrosted the coils and it came up to about ten. I charged the unit with 8 pds of R22 and got the low pressure to hang around 29 with a sat temp of 8 and the high sat temp is 60.
So i have been checking this thing every day, its in my town. And the evaporator (one farthest from door is still frosting) and the expansion valve on the other side is starting to frost.
So did a more through check. The deforst timer out on had three pins set to 2 6 hour runs and one 12 hour. I add one more pin so now it has 4 30 min defrosts set at six hours each. Checked the thermostat, It doesn't kick out the condenser at all, but the power does cut when the temperature is bumped.
So here is the crazy thing it has a defrost timer set inside the cooler it self set to two defrost times midnite and noon. I believe this timer runs up two a solenoid in the liquid line. Have no clue what this is for.
I hope that was enough information, like I said my main focus is residential, any help or suggestions much appreciated. Please let me know if more info is need or if I am just nuts.
wow... Your all over the place.... Not sure I'm understanding you correctly but if the t-stat doesn't "kick out the condenser at all" It would be a good place to start.... Followed by...
Is the sight glass full???
Are there R22 txv's in the coils???
Is the defrost clock working???? What are the 2 clocks controling????
Is the LLSV working????
Find the leak don't just keep to topping it off... And if u put a piercing valve on then take it off and braze something in there....
There's alot more but just the basics will tell u alot... U might want to give pops a call if you don't understand what a solenoid does...
Does the compressor have a low pressure control? Typically the thermostat only shuts off the refrigerant to the evaporator by closing the liquid line solenoid. The compressor then pumps gas out of the evaporators until the pressure reaches the cut out setting on the condenser's low pressure control. Likewise when the tsat opens the liquid line solenoid valve (LLSV) pressure rises and causes the compressor to start.
Does the LLSV close completely? If the condenser runs for several minutes after the tstat shuts down then the LLSV is suspect in your freezing problem.
What is the differential on your tstat? 5 degrees is about a minimum. Typical tstat settings are 38 degrees on 33 degrees off.
If the customer is setting lower temperatures and you do not have defrost heaters that is part of your problem too.
What is your TXV superheat? A walkin is typically 8 degrees +- 2.
A restricted or improperly set TXV can cause icing problems. Your suction pressures are too low. R22 I would expect to see 40-50# (more if the box is warm). Are the evaporators clean?
Are the evaporators sized properly to match the condenser. If you have no info on the condenser the compressor data should be able to give you a ballpark. If the compressor is too big that could be part of your problem.
Have you found any leaks to justify adding refrigerant. Just because pressures are off is no reason to add refrigerant. Many other things can cause low suction pressures.
txv system should have a sightglass..bet the 2nd evap is freezing up cause the txv is being underfed due to low refrigerant..
..bet you find the tap valve leaking..
sweat in an acess tee where needed on suction & liquid lines& can the tap valve
like said it should be a pumpdown system- with 4-30 min defrosts you shouldnt be having freeze ups--
I figured I left some stuff out.
Sight glass is clear (no bubbles). I found a small leak in the old Liquid service valve, fixed that with the leak lock. Have been over entire system with detector and haven't found any other leaks (I know its not 100%) but next step would be a dye. Evaporators are clean I made sure when I defrosted the first time.
The second defrost timer I mentioned (inside the cooler) is hooked up to the solenoid in the liquid line it is located before where they T to run into the evaporator coils. The timer is set for Noon and Midnite. What I don't under stand is why it is hooked up that way.
I also have no information on the evaporators. The compressor is sized off of the old one so I assume it is sized properly.
The defrost on the condenser does work 4 sets of 30.
The t-stat is set with a 4 degree variance 32-28 (customers request for milk).
As far as I know the cooler it self was brought in from TN (I believe) and hooked up to the existing equipment, which the condenser is still original I know for sure.
As far as the LLSV I was wondering if the tried to bypass the t-stat some how with the second defrost control.
I going there tomorrow, mainly I was just curious about the second defrost in the cooler it self and if anyone has a "oh thats it" for me.
Thanks alot for the info guys.
on walk in leaks..always look at txv-especially if its a flare connection...
also at txv/evaporator feeder tubes..on solenoid bodys..even the sight glass ive seen leak.
If service valves are leaking at the stem, try tightning the stem packing. Suction temps/pressures are way too low in your post for a cooler. Should be around 43# or so with r-22 giving you a saturation temp of around 20* in the evaporator. If you added that much freon and you suction did'nt come up any more than that, then I would say( especially at this point), we have enough freon. Check superheat to see how much of the evaporator to txv is supplying with liquid. If superheat is really high, take the sensing bulb off the suction line and hold in your hand. If your suction pressure rises some or your superheat goes down some, then your valve is throttling. If You just can't get it to change any, you could have a bad txv. Have you checked for restrictions such as filter dryer etc. Lots of things don't add up here.
You said "the sat temp on the high was 60"
If thats you sct it seems low you may want to look into that.
I can't get use to this trouble shooting over the computor stuff. I have done it for years with one of my guys or a friend (what have ya) on the phone. But they are usually at the unit telling me what they see, and checking what I tell them too.
28 degrees is too cold for a walkin that does not have heating coils in the evaporator. Especially if the tstat keeps the compressor on most of the time.
Originally Posted by powellHVAC
There's one source of your icing.
You replaced a bad compressor, even if the new one is the same size the old one could have had bad valves and been unable to pull the suction pressure so low. Possible reason icing started after the compressor was replaced.
The box and condenser were not a matched set. (from you just said about the boxes origin.) Mismatch could cause low suction. An evaporator pressure regulator might solve that problem, but you must first make sure everything else is right.
Have you verified superheat? Too high of a superheat could be why the suction pressure is low. Low suction promotes icing. If you find that superheat is high make sure you monitor the compressor amps to not overload it as you lower the superheat. (Especially with the unknowns involved iin the match up of the evaporators to the condenser.)
Bad gaskets on the doors allow warm moisture laden air to enter. Contributes to icing two ways. First directly with additional moisture. Second by increasing the BTU load and forcing the compressor to stay on longer. The off cycle acts like a mini defrost and helps remove moisture/ice.
Originally Posted by surenuff
What is your head pressure? If its below 150-160# you need to get it higher with a fan cycling switch, headmaster, or an electronic fan speed control. Low head pressure could be why you have low suction. The TXV needs about 80-100# difference between high side and low side to work properly. (In a well designed system. In a cobbled together unit ????)
Had an idea as to why you have two defrost clocks. Wherever the box came from originally they had mounted the defrost clock inside the cooler. The old box that was removed or was the original paired with your old condensing unit had the defrost at the condenser. And when they cobbled the two together they were too lazy to remove one of the clocks. Figure out which one works, and if they both do, disable one of them (take the pins out) and use only one clock. Or better yet talk the customer into cleaning up the wiring and remove it completely.
28* too cold? are you talking about the evaporator? Coolers are normally set to use off cycle defrost. No heaters of any kind. Sometimes someone will install a clock to give timed dedicatied defrost, but it is usually something that could have been fixed instead of adding a clock. Evps run 10-20* cooler that box temp.
Bad information is worse than no information at all.
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