kys0r/warren produce case not cold enough

[shawn626]

Hey guys, I was recently asked to look at an r 22 produce case wich the customer complained isnt cold enough to display meat in. Here is what I found: The head pressure is 250 psig or 114 degrees f. Air enters the condensor at 74 degrees f and leaves at 105 degrees f. thats a 31 degree td. the case temp wont drop below 43 degrees f. The suction pressure is 48 psig or 24 gegrees f. Air enters the evap at 55 degrees f and leaves it at 37 dgrees f. thats a 18 degree td. the superheat measured at the compressor is 15 degrees f. design specs state that the air leaving the evap should bebetween 28 and 33 degrees f. The air temp in the store is 73 degrees f.To mee none of theses numbers seem terrible out of the ballpark. The compressor will also pull down into a vacuum easily. What could the most likely cause be?

[750 Valve]

on the refrig side - does it have a correct charge? what is the subcooling like?

on the case side - is the coil dirty? is the honeycomb blocked?

[kas]

is the evaporator clean , good air flow through it ? check refrigerant charge

[nike123]

Why is such a difference in evaporator air in temperature and case temperature? It should be pretty much same! Do you have any additional thermal loads near the evaporator inlet or maybe store air is somehow mixing with return air from case in to his path to evaporator inlet?

[Gary]

Is the case connected to a rack system?

If so, you will need to visually inspect for malfunctioning evaporator fans and/or frozen coil. Frost towards the rear of the sheet metal coil cover is an indication of frozen coil.

Also, you will need to check the superheat at the evap outlet.

[Gary]

Why is such a difference in evaporator air in temperature and case temperature? It should be pretty much same! Do you have any additional thermal loads near the evaporator inlet or maybe store air is somehow mixing with return air from case in to his path to evaporator inlet?

Supermarket cases usually place the case temp sensor in the supply air at the top of the case. The temp is closer to evap out than it is to evap in.

Also important to note on a multi-deck system: The supply air feeds up through the back panel and is distributed along the way, therefore the air supplied to the bottom shelf will be colder than the air supplied to the top shelf. Normally this difference is small, but if the supply air is decreased (fan problems, frozen coil) the difference from bottom to top can be very substantial with little or no chilled supply air reaching the top.

According to the OP, the evap in is 55F and the evap out is 37F for a 18F dT. We need to know if the evap out was measured close to the evap coil. If the measurement was taken higher up in the case, the actual dT could be much higher, indicating airflow problems.

It is best to pull the product from the bottom shelf and visually inspect the fans and coil.