View Full Version : Iced up suction line.
02-13-2007, 06:57 PM
I am having occasional trouble with a reach-in 6 door freezer. The customer is using it for frozen food and icecream. I got a call from him last night that the temp inside the freezer was 28 deg. F. I was out of town until this afternoon and when I stopped to look things over the temp was at -5 deg. F Most of my experience in the field of HVAC was in Airconditioning. I have done this work on the refrigeration side of the spectrum out of nessecity. Any way I changed out a semi-hermetic compressor a few months ago and had not had a call on it in a about 2 months. I had to change a defrost timer which was rusted from the previous techs lack of interest in protecting it from the weather. What I need to know is this...why does the temp fluctuate like I have noted above? I am having a good bit of ice build up on the evaporator coil on one side only ( opposite the TXV.) I had retro fit this unit about two years ago from R-12 to R404A. It has a receiver that could easily hold 30 lbs + of refrigerant. I charged it to about 17 lbs. It was a warm day when I charged the system and the sight glass showed no action. I let it run with a small amount of frozen food in it to maintain a load. It ran perfectly for two months!
I don't recall what the super heat was at the compressor. After 1 month I noticed a small coating of frost on the suction line back to about 12" from the compressor. (I live about a block from the store and I ride by daily.) Is there something I'm missing here? Could it be undercharged? Should the condenser fan have a longer off cycle on the cycling pressure switch as this is the only low ambient control on it. The defroster elements show continuity through them. Would they show it if they were bad or shorted? HELP GUYS!!:confused:
02-13-2007, 07:08 PM
Your coustomer could have caught it at the end of a defrost cycle. Even tho to me 28 seems way high.. But what are the pressures and amperages. Did you block the condenser off to get ur head pressure up and check the glass to make sure its clear? Dont just test resistance of the heaters. Put your amp meter on the heaters to insure there working correctly. The suction line should ice back.
02-13-2007, 07:35 PM
What kind of coil temp are you running? Almost sounds like you have a dirty screen in the tev and are starving the coil. Most of the ice cream cases we deal with run about a -25 coil and depending on the system like 6-15 on SH. That POE will clean a system out and clog up filters and screens.
Try some basic system checks first.
02-13-2007, 08:00 PM
94blowncobra, are talking about SH at the compressor or the evap?
02-13-2007, 08:31 PM
94blowncobra, are talking about SH at the compressor or the evap?
Evap coil. Should have no less than 20 degrees SH at the compressor.
02-13-2007, 08:37 PM
what is your evaporator superheat? What is the discharge air out the honeycombs. What is the length, event and termination of the defrost clock? How is it controlled for temperature? What is the head pressure fan cycling switch set for?
You have next to nothing in information for a guy to even try and help.
02-13-2007, 09:01 PM
Check all of the previously mentioned stuff.............also check to make sure the defrost heaters are positioned under the evap coil. On older cases especially, the platform on which the heaters sit, or the heaters themselves will move. As a rule when they do, its toward the front of the case (which would tend to allow frost to build on the back side of the coil.
Like the others said though - more information would be great.
02-13-2007, 09:17 PM
Ok, when all this freezing rain ends I'll get up on the roof and check! Thanks for pointing out some facts I overlooked.
not to bust your beans, but did you put a low temp compressor in there?
02-14-2007, 07:25 PM
Yeah Len, it is a low temp compressor.
02-14-2007, 08:42 PM
Defrost stratigy? How many defrost? Is it constantly frosting over and losing air flow before the next defrost? Air flow adaquate?
Doors all close? so to speak frost can not build when no moisture gets inside. Do the fan switches on every door work, or is one of them by the chunky monkey sticking pulling warm moist air in when customers stand there for ten minutes before buying exactly the same thing they did the last 25 times they went shopping.
The info supplied is far to vauge to do more than guess and those are my first guess's on a box that can and will pull down and just has the occasional freeze up.
I have gone on weekend calls for mega bucks to find a case of biscuts holding a door open and the coil totally frozen over and nothing else was wrong.
02-14-2007, 09:07 PM
As far as I can tell there is nothing keeping the doors ajar. I have a t-stat that turns the fans off when the system goes into defrost. Until I can get on the roof to check other things out i am just gathering technical assistance from you guys. I failed to mention that it is a pump down system. I'm begining to think i have a combination of problems. i plan on hitting the roof tomorrow afternoon, so i may have more info.
02-15-2007, 09:12 AM
It could be under charged which would show in colder weather. Fan should not cycle if it has a headmaster. was it 28F after a defrost or is that the normal cycle range? How many defrost in 24 hrs.? Just from your description I would think undercharge but ck SH at evap and comp. If this is the coldest normal weather in your area, now is the perfect time to charge it properly.
02-16-2007, 03:09 PM
If the receiver holds 30#'s and you charged only 17? Why? If it was cold outside, use subcooling and check your glass to charge proper amount. Sounds like you didn't add enough charge and as the temps dropped, it got more noticable.
04-13-2007, 04:40 PM
I meant to say R408 not R404. I did find a non-operational TXV though. The defrost wiring was totally shot Broken conductors inside the conduit!. Can anyone cross this TXV number It looks like a 5BFRE AA ZP. The "5" could be an S and the "Z" could be a 2. 3/8 sae flare supply & 1/2 flare outlet. It is a R502 valve. It might be a Sporlan product.
04-14-2007, 08:56 PM
Can anyone cross this TXV number It looks like a 5BFRE AA ZP. The "5" could be an S and the "Z" could be a 2. 3/8 sae flare supply & 1/2 flare outlet. It is a R502 valve. It might be a Sporlan product.
Yes it is. Likely a "BFRE-AA-ZP" if it has 3/8 x 1/2 SAE connections. A balanced port R-502 TEV which is also suitable for R-408A. An "SBFRE-AA-ZP" would have 3/8 x 1/2 ODF connections.
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