Defrost Timers for Commercial Refrigeration: 8145-20 & Grasslin Explained

Every mechanical or electronic refrigeration system needs a way to melt frost off the evaporator coil before it builds up enough to block airflow and kill cooling capacity. That job belongs to the defrost timer — a small, easy-to-overlook part that causes big, confusing symptoms when it fails.

How a defrost timer works

On a set schedule — commonly every 6 or 8 hours, regardless of what the thermostat is doing — the timer briefly stops the compressor and energizes a defrost heater (or, on some systems, reverses refrigerant flow) long enough to melt accumulated frost off the coil. Once the defrost cycle ends, normal cooling resumes. A mechanical timer does this with a motor-driven cam; electronic timers use a circuit board on the same basic schedule logic.

Symptoms of a failed defrost timer

• Heavy ice buildup on the evaporator coilthat keeps growing instead of clearing on schedule — the most common symptom, and one that's often misdiagnosed as a refrigerant or compressor problem.
• Warm box despite the compressor running constantly — an iced-over coil can't transfer cold air even though the system never shuts off.
• Compressor never runs at all — if the timer is stuck in the defrost position, it can hold the compressor circuit open indefinitely.

8145-20 vs. Grasslin — telling them apart

“8145-20” is a Paragon model number for a widely used 24-hour mechanical defrost timer found across many refrigeration and ice machine brands — its ubiquity is why it's often searched by number alone. Grasslin (part of the Intermatic family) makes a separate defrost timer line with its own model numbering. The two aren't automatically interchangeable just because both are “a defrost timer” — always cross-reference by your equipment's original part number rather than assuming a brand match.

Find your equipment's original part number first

The defrost timer is usually mounted near the compressor or control box; the part number is printed directly on the timer body or its wiring diagram label. This is the fastest way to confirm an exact replacement — see our general worn-parts replacement guide for the full diagnostic process.

Not sure which timer you need?

Email the part number printed on your existing timer, or your equipment's model and serial number, to info@prokitchenspares.com and we'll confirm a compatible replacement.