The condensing unit holds the compressor and condenser and sits outside or on the roof, rejecting heat. The unit cooler, also called the evaporator unit, hangs inside the box and holds the evaporator coil, fans and defrost parts. Refrigerant lines connect them. Knowing which half a problem belongs to speeds up repair.
In a split or remote walk-in, the system is two halves joined by pipes. Each half has its own parts and its own typical faults.
Comparison
| Item | Condensing unit | Unit cooler |
|---|---|---|
| Location | Outside, on the roof or a pad | Inside the box, near the ceiling |
| Main parts | Compressor, condenser coil, condenser fans, receiver, controls | Evaporator coil, evaporator fans, drain pan, defrost heaters, expansion valve |
| Job | Compress refrigerant and release heat | Absorb heat from the box |
| Exposure | Weather, dirt, heat | Cold, moisture, ice |
| Typical issues | Dirty coil, fan failure, electrical faults, leaks | Ice, fan failure, drain and defrost faults |
Condensing unit parts
- Compressor, contactor and capacitors.
- Condenser coil and fan motor.
- Receiver, high-pressure switch and low-pressure switch.
- Head pressure control and crankcase heater.
Unit cooler parts
- Evaporator coil and fan motors.
- Expansion valve.
- Defrost heaters, termination switch and fan delay.
- Drain pan and drain line heater.
Which half is the problem
A hot outdoor unit that trips is a condensing unit problem. Ice on the coil, weak airflow inside the box or water leaks are unit cooler problems. A bubbling sight glass or oil stains at fittings can belong to either, or to the line between. Describing where you saw the symptom helps the technician start in the right place.
Matching the two
The two halves must be sized for each other and for the box. A condensing unit that is too small will run constantly, and one that is too large will short cycle. The unit cooler must match the load and defrost method. When replacing either half, ask the technician to confirm compatibility, refrigerant and line sizes before ordering.
See self-contained vs remote, the systems guide and the parts guide.
Service access and safety
Condensing units on roofs or pads need safe access, with a ladder or stairs, working lighting and a lockable disconnect within reach. Unit coolers sit above head height inside a cold room, so service means ladders in low temperatures. Ask the installer how each half will be reached before the box is built, because awkward access raises service time and cost for the life of the system. Keep the area clear around both halves so a technician can work quickly, especially in an emergency.
Warranty and records
Keep the model and serial numbers of both halves, the refrigerant type and the installation date. They are the first things a technician will ask for.
Questions about this topic
Is a unit cooler the same as an evaporator?
The unit cooler contains the evaporator coil along with fans and defrost parts.
Can I replace only one half?
Sometimes, if they are compatible. A technician should confirm.
Why is the outdoor half louder?
It contains the compressor and large fans.