The clock motor of a mechanical defrost timer on a walk-in freezer has stopped turning. What will happen over the next few days?
- Defrosts will start too often, and the box will warm up
- No defrosts will start, and the coil will ice up solid
- Heaters will stay on constantly, and the limit will trip
- Fans will stay off constantly, and the suction line will frost
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B. No defrosts will start, and the coil will ice up solid
The timer motor advances the dial that initiates defrost. If it stops while the system is in the refrigeration position, the system keeps cooling with no defrost at all, and frost builds until airflow through the coil is blocked.
Reference: Walk-in freezers; defrost timer failure
Heavy frost keeps building on the part of a walk-in cooler evaporator nearest the door, and the door gasket is torn. What is the cause?
- Refrigerant leaking out at that end of the coil
- A defrost heater that has failed at that end of the coil
- An expansion valve feeding only that end of the coil
- Warm, humid air leaking in and freezing on the coil
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D. Warm, humid air leaking in and freezing on the coil
Outside air drawn in around a bad gasket or a door left ajar carries moisture that deposits as frost on the first cold surface it meets. Fixing the door stops the moisture at its source.
Reference: Walk-in coolers; infiltration and frost
A reach-in cooler in a kitchen has a warm cabinet. The compressor is very hot and cycles on its overload, and the condenser fins are matted with grease and lint. What is the first step?
- Add refrigerant until the suction line sweats
- Clean the condenser coil and check the condenser fan
- Replace the compressor start relay and overload
- Lower the cabinet temperature control setting
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B. Clean the condenser coil and check the condenser fan
A blocked condenser cannot reject heat, so head pressure and amp draw climb until the overload opens. Cleaning the coil restores normal pressures; adding refrigerant would make the high head pressure worse.
Reference: Reach-in refrigerators; dirty condenser