looked at a medium temp walk in today running to cold. found it was getting to about 30 degrees. has a johnson control a419 temp control. checked it against my fluke 52 digital. it seems to be reading about 5-6 degrees off actual temp. ohmed out sensor per manual. got 900 ohms at 40 degrees. right on spec. so i guess that means temp control is bad? sensor ohms correct but temp control reads 44 when actual temp is about 38. box about 10 yrs old, sensor never moved or anything like that.
also low suction(35 psi with r22) at 35 deg. box, while very low sh, about 1-3 degrees. sight glass clear, fans both on, im thinking coil must be dirty inside restricting airflow. any help appreciated. thanks