The short answer
On this generation the defrost circuit is a timer, a heater and a terminating thermostat, and any one of the three stops the whole cycle. Ranked first on this platform: The defrost heater, timer or terminator. The checks below follow that ranking, and the first of them need no tools and no panel removed.
What you observe
- The cabinet cools well for a week or two after a manual defrost and then drifts again — A fault that resets when you defrost it by hand is a defrost-circuit fault.
- Frost building along one part of the door or lid line — Frost marks the entry point of the leak as reliably as smoke marks a draught.
- It runs almost constantly and the air coming off the back is hot — Long running and hot exhaust is a coil that cannot let go of its heat.
- NEAR MISS — the cabinet is silent and nothing runs at all — That is a supply or start-circuit fault, and it is diagnosed from the outlet inwards rather than from the coil outwards.
Causes, most likely first on this platform
- The defrost heater, timer or terminator — On a frost-free cabinet three parts have to work together to clear the coil: something to decide it is time, a heater to do it, and a thermostat to stop it. It ranks first on this platform because a mechanical defrost circuit gives no warning: the cabinet runs normally while ice builds on the coil for a fortnight and then stops holding temperature in a couple of days, which is why owners report it as sudden.
- A door or lid seal that has stopped sealing — A freezer has a bigger temperature difference across its door than any other appliance in the house, so a seal that leaks costs it more. It ranks second here because a cabinet of this vintage has wear on everything at once, which changes the ranking: the parts that wear are far more likely than the parts that break.
- A blocked or dusty condenser — The condenser sheds the heat the cabinet takes out of the food. It comes third in the order — a genuine cause here, behind the ones above it on frequency alone.
Check in this order, and why
- Note how long it takes to fail again after a full manual defrost — That interval is the single most useful piece of information you can hand a technician. It leads because it tests the top-ranked cause.
- Close the door on a slip of paper at a dozen points round the frame — It maps the seal in two minutes with nothing but a piece of paper. Tests the second-ranked cause.
- Look at the coil at the back or behind the lower grille — Grey felt across the fins is visible without dismantling anything. Tests the third-ranked cause.
What an owner can safely check
- Clean the gasket with warm soapy water, dry it and repeat the paper test — Also look for a hinge that has dropped, which produces the same result at the bottom of the door.
Tools: clothAbout 20 min
- Unplug the cabinet and vacuum the condenser and the compartment around it — Work along the fins, not across them.
Tools: vacuum, soft brushAbout 20 min
- STOP at the first panel that needs a tool, and write up what you found — A technician who arrives knowing which checks came back clean spends the visit fixing rather than repeating them.
Before you open anything
Safety
Unplug the appliance or switch off its breaker before removing any panel — a capacitor can hold a charge after the power is off.
When to call a technician
Call once the door, the airflow and the condenser are all clean and the cabinet still drifts, because what remains is a defrost circuit or a sealed system and both are measured rather than looked at.
Nearest pages of this class
What this page does not cover
This page is written for the Moffat freezer as a class, not for one family or one model line. Where a family- or model-specific page exists for your unit, that page is the more specific answer and the one to read first. Deliberately not here: part numbers, wiring colours and disassembly order, which differ by family.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
