tk super 2 30 sr cooling issue

[zombie]

Hey guys, I ran into a unit that i'm having trouble with and have reached a mental block on. It's a thermo king super 2. If I remember right it is an early 2000's with a micro 4 in it, no modulation, no etv, has an x430 in it with a yanmar in front of it. It is very slow to cool even with a divider door in trailer. In high speed cool, rpm is 2185, low side at suction service valve is 41psi, high side is 225psi, discharge air is 40f, delta t is -9f, coil is 36.7f, ambient 68f, and box temp 49f. Ball in receiver tank is at top of sight glass. At the bottom of the expansion valve where it is soldered to the distributor manifold it frosts up immediately. This unit just received a new expansion valve for the same issue and the feeler bulb has good contact. Any ideas? I hate to admit it, but having such a large fleet to maintain, something out of the ordinary has sent me for a loop.

[cadwaladr]

It's down to basics time,does the system pump down via shutting the receiver?,does the compressor pump down ie closing the compressor suction valve head pressure appears low to me which is why I recommend doing the basics,of course I presume the drier has been changed?

[zombie]

Thanks for the reply. I'll try to get back to it tonight and do a low side pump down and a compressor pump down. I thought head pressure was low and suction was high. The drier was changed at the time of the expansion valve and the line was blown out between the two.

[zombie]

I was able to get back to it last night. Did a low side pump down but left the discharge service valve open and it held 15" of vacuum for about 10 minutes. I moved on and did a compressor capacity test. Head pressure was controlled at 320psi, and when low side reached 10" the high side was at 250, in spec according to my tk book. At this point, management didn't want to spend anymore time on it and tk will probably be out to look at it and another problematic unit today. I will update if I can find out what they did.

[IRMechanik]

From your original post. I would say your discharge is decent based on ambient, your suction is decent based on box temp. But your coil temp is a little low. Generally your coil temp should hover somewhere between return air and discharge air. Sensor accuracy isn't the uP IV strong point but I would look at air flow, possible dirty evaporator. been a while since I've seen a stupid II so grain of salt.