transicold reefer

hey guys been working on a transicold reefer operating at at -18 setpoint initial problem was compressor iceing up partially, worked with another engineer decided to charge the unit up , it was then decided to pull the gas out and vac the unit out and weigh in correct charge .compressor still iceing up ,pressures are within range and fans cycling on and off to requirements, also unit runs on r134a.I came to the conclusion that the suction modulation valve is not closing fully and hunting once unit has reached its set point and comp switched off. I have checked the resistance (that ok) and checked the display which says its open 21 percent when unit has reached setpoint and thats really all i can do without the proper testing kit for it. if any one has any ideas please let me no cheers.

whats it on a 69nt they will ice a little the modulation valve subcools the windings what temp is box when it starts iceing

yes its 69 nt but i believe it is the quench valve tha cools the windings and the mod valve which regulates the suction into the compressor based system pressures, its -18 return and supply temp is -22 ish

after checking the unit today i found that the freezing of the compressor is occuring because, once the defrost temp reaches 5 degrees the heaters disengage the condenser fans start cycling along with the compressor but the controller still indicates defrost mode but with no heat led displayed, at this point the evap fans are not running it is my assumption that the controller module is faulty as this is not the normal mode of operation .

the windings are cooled through the mod valve on provision the entrance to comp is on the front of comp on base of comp if its on the back its just a leveler if mod is gone we remove them and fit a dixell or eliwell some of the carrier mods have a delay after defrost to allow recovery