low temp drop

[wsellers]

Hello, i've sold my hvac business and moved to a new area for a new start in business due to my childrens education and other personal reasons. I'm attempting to get started here in a rural area and am branching out into just about anything associated with refrigeration. so far ice machines, freezers, and now a reefer unit.
I'm still trying to get down the basic operations of these units but the current problem I'm having with this unit is an apparent insufficient feed to the evapaorator coil. I evacuated and weighed in the charge in this unit because it has an unknown history. the pressures in this tk model kd-11 with 7lbs of 404a is 25psi low and 275 high with a box temp of 85 and outdoor is about the same. the temp drop across the coil is very little and my diagnosis of this with equipment that I am familiar with would be a txv not opening sufficiently. my concern is if there is a control in the circuit that could also be causing this type problem. thanks

[cadwaladr]

the pressures seem right,there is a data plate on the unit frame are you sure its 404a,the correct charge weight is stamped on this plate,it will take some time to get the heat load from the cargo area is the insulation/door seals ok

[wsellers]

the nameplate states 404a and the charge weight of 7lbs. the expansion valve head is a 404a head. I have evacuated and charged with new 404a because I don't know any history on the unit. the owner has run the unit for several hours with the box temp not getting below 50 degrees. I will check the box seals. I'm not familiar with freezer operation with a high box temperature but there seems to be insufficient refrigerant feed to the evaporator (not much temp drop across the evaporator), and superheat is very high. I don't have subcooling or superheat measurements yet but the suction line back to the compressor is probably 65 degrees. thanks for the reply and I will check the box seals tomorrow and any other suggestions. thanks

[bellg]

As Cadwaladr already stated pressures look to be reasonably good.
Has anybody been tinkering with the expansion valve? Did you try a compressor capacity test - will it pump and hold a good vacuum and build up good head pressure?

[wsellers]

I have a new exact replacement expansion valve in hand and plan to install it tomorrow. i have not done a pump down on the unit to check the compressor but I will before replacing the valve. the valve power head was replaced at some time and the valve looks as if it has been roughly handled due to dings in the brass body. when the replacement power head was installed the bulb line was allowed to wrap around the valve under the power head as the head was threaded onto the valve body. this looks as if it could have even damaged the line to the bulb. i am beginning to wonder if i may have a dual problem. possibly an expansion valve not feeding properly and another problem causing the pressures to look somewhat normal. as i stated about the supply air coming from the evaporator, it seems conditioned very little and there is a definite warming of the supply air from one end of the evaporator to the other which seems to indicate an insufficient feed from the tev. thanks for the reply and any info in regards to a expected temperature drop across the evaporator coils would be helpful as well as superheat or subcooling expectations. thanks

[bellg]

Any update on that unit. was it the expansion valve?

[clivemtk]

did u replace drier

[Gary]

I'm guessing there is nothing wrong with the TXV, the superheat is high because the box temp is high, the dT is low because the system is removing lots of moisture from the box and it is going to take days, not hours, to dry it all out and get it down to temp.

But I would check/clean the TXV inlet screen... just in case. :)

[wsellers]

thank you for the replies. after replacing the txv, inlet screen, and filter drier the unit is running correctly. the box temp as was suggested did drop more slowly than I would have ever guessed, but it did get down to the correct temp. the inlet screen did have significant build up in it so it could have been the primary problem. nevertheless it is operating very well and I appreciate greatly the help. sorry for the delay in getting back with a report.