Not cooling · Is the refrigerant going?
Why Is Only One Corner of the Coil Frosted?
- Signed
- Dean Halvorsen
- Role
- Refrigeration technician — sealed systems and airflow
- Certification
- EPA Section 608 certified
- Published
Short answer
The coil is being underfed. When too little refrigerant reaches the evaporator, what does arrive boils away in the first stretch of tubing, so frost collects there and the rest stays bare. A leak or a partial blockage can each cause it. Sub-Zero Repair Edmonds starts working out which for the $89 service call: (206) 210-3547.
Even frost and patchy frost
The evaporator (the cold coil behind the back panel of each section, where the refrigerant soaks up heat from the air) picks up frost while it runs, and the defrost clears it at intervals. Two patterns are not normal. A coil packed solid from end to end usually points at the door, the fan inside the section or the defrost itself. A coil frosted only across its first few passes, with the far end bare, points somewhere else: the refrigerant is running out before it has travelled the whole coil.
The refrigerant boils as it takes in heat. With a full charge it works along the whole coil; with too little it is spent early, and most of the coil barely cools the air.
A leak or a blockage: the gauges decide
Two faults starve a coil in this way. One is a short charge, meaning refrigerant has escaped. The other is a partial restriction, something narrowing the path into the coil; Sub-Zero’s service manuals list a plugged capillary tube (the very fine tube that meters refrigerant into the coil) and moisture in the system among the causes.
The frost cannot tell them apart. Pressures can: in Sub-Zero’s manuals, low readings on both sides of the system point to a leak, while low on the coil side with high on the condenser side points to a restriction. The two repairs differ, so topping up refrigerant on the strength of the frost alone is a guess.
You are unlikely to see this yourself: an owner notices a section drifting warmer, and the frost shows only with the panel off.
What it may cost
$89 to find out — the visit and the diagnosis, taken off the repair if you go ahead.
- Compressor or sealed-system repair Shows as a compressor that clicks and will not start, or refrigerant slowly lost $1,300–$3,270
Ranges, not starting prices. The technician names one figure inside the band before any panel comes off, and Sub-Zero Repair Edmonds holds to it.
Wait or call today?
Can wait until morning
- Food is still cold, 40°F or under in the fridge with a firm freezer, and the change has been a slow drift.
- You have been told about the frost pattern but the food is still cold: keep the doors shut and book a visit.
Call today if
- The freezer has started to soften, or the fridge thermometer has passed 40°F.
- The unit now seems to run without ever resting, and it is still getting warmer.
Anything in the second card is a reason to phone Sub-Zero Repair Edmonds on (206) 210-3547 today rather than tomorrow.
Questions people ask next
Should I scrape the ice off the coil myself?
No. Prising at ice on an evaporator risks piercing the tubing, which turns a starved coil into an open leak. On a built-in the coil sits behind a panel in any case, and patchy frost is a clue to be read rather than the fault itself. Sub-Zero Repair Edmonds looks at the pattern with the panel off: (206) 210-3547.
Will switching it off to melt the frost fix it?
It clears the frost, not the reason for it. If only part of the coil frosted because refrigerant is short or its path has narrowed, the same pattern grows back once the unit runs again. Melting it first can also wipe away the evidence a technician wants to see, so leave it alone and keep the doors closed until the visit.