Sealed System Diagnosis Visit
Purpose
A sealed-system verdict is commercially irreversible. Once a tech says "it's the compressor" the customer is choosing between a large refrigeration repair and a new refrigerator, and if the real fault was a choked condenser the shop has either sold work nobody needed or lost the job to whoever found it. This procedure guarantees every non-sealed cause is eliminated, with a reading beside it, before the sealed system is named.
It also guarantees the system is not opened casually. Opening a small appliance sealed system is a regulated act under 40 CFR Part 82 Subpart F requiring EPA Section 608 Type I certification and recovery, so a gauge set going on is a decision, not a diagnostic reflex.
Scope
Residential refrigerators, freezers, ice makers with their own sealed system, and wine and beverage coolers. Covers diagnosis up to and including the classification of the sealed-system fault.
It does not cover recovery, evacuation or recharge; the refrigerant recovery SOP owns those and step 8 hands off to it, nor the repair-or-replace recommendation, which its own standard owns. On variable-speed inverter systems the current comparison in step 6 does not apply and the manufacturer's service data governs, because a variable-speed compressor's current follows commanded speed rather than load.
Roles and the handoff between them
| Role | What they own | What they hand off |
|---|---|---|
| Office at booking | The temperature complaint with the customer's own reading if they have one, and how long it has run | Duration on the ticket: a cabinet that warmed over weeks and one that warmed overnight point at different families |
| Technician | Elimination of defrost, airflow and control faults with a reading for each, then the external sealed-system read | A classification with its evidence, or a non-sealed fault corrected and a re-check scheduled |
| Type I certified tech | Any act that opens the system | The recovery record, under the recovery SOP |
| Office after the visit | Scheduling the pull-down re-check | A re-check appointment with the target temperature and the time the clock started |
Before you touch the machine
Identify the refrigerant off the data plate before anything else. Domestic units built in recent years commonly use R-600a isobutane, which is flammable and permitted at charges up to about 150 g under UL 60335-2-24. If the plate says R-600a: no open flame, no smoking, no sparking tools, no soldering near the cabinet, ventilate, and no flame-based leak detector. Keep ignition sources out of the compressor compartment, where a leak collects because isobutane is heavier than air.
Prove the appliance dead before removing any panel that exposes a terminal, the defrost heater circuit, or the compressor. Unplug, then verify at the terminal block with a meter proved live on a known source before and after, which is NFPA 70E-2021, 120.5. Work practices for this class sit at 29 CFR 1910.333(b)(2).
Fins cut through thin gloves. Cut-resistant gloves before a hand goes behind the evaporator cover or into the machine compartment. Defrost heaters and discharge lines stay hot after shutdown; check with the back of a gloved hand first.
The procedure
Read the cabinet with your own instrument and record the duration. Calibrated thermometer on the middle shelf of each compartment, read after the doors have settled. Acceptance: both temperatures written against the control setpoints. Wrong looks like accepting the built-in display, which reports setpoint or a sensor position rather than the compartment. Stop rule: both compartments within a few degrees of setpoint on a spoilage complaint means door usage or defrost timing, not a sealed system.
Read the evaporator frost pattern before anything else. Pull the cover and photograph the coil. Acceptance: even light frost across the full coil face. Wrong looks like an ice slab over coil and drain, which is a defrost fault, or frost on the first passes only, which is a charge or restriction signature. Stop rule: an ice block sends you to step 3 and no further. Never chip evaporator ice with a screwdriver; a punctured tube turns a defrost call into a sealed-system replacement.
Test the defrost circuit as components, not as a system. Unit proved dead, measure heater resistance and the bimetal or thermistor state cold, then read stored defrost history if the model keeps it. Acceptance: resistance within the tech-sheet band and the terminator closed at freezer temperature. Wrong looks like an open heater or a terminator that never closes. Stop rule: a failed defrost component is the fault; correct it and stop, because defrost failure produces warm cabinets that look exactly like low charge.
Verify airflow on both sides. Run the evaporator fan with the door switch defeated as the tech sheet directs, confirm the condenser fan runs when the compressor runs, and inspect the condenser face. Acceptance: both fans turning at speed and a condenser you can see light through. Wrong looks like a condenser packed with lint, or a blade that spins freely because its motor stalled under load. Stop rule: a restricted condenser or stalled fan is the fault; correct it and go to step 8. Keep fingers clear of the condenser fan when defeating a door switch.
Confirm the compressor is commanded and starting. Check for supply at the compressor or inverter input when the control calls, and listen for the start attempt. Acceptance: correct voltage at the terminals during a call and the compressor running rather than opening on overload. Wrong looks like locked-rotor current for a few seconds and a repeating trip. Stop rule: no voltage during a call is a control fault. Energized measurement: intact leads, one hand, stance clear.
Read the sealed system from outside with temperature and current. Compressor running at least 10 minutes, read condenser inlet, mid and outlet, drier body and outlet, capillary entry, and suction line at the compressor, then read current. Acceptance: a written profile plus current compared against the plate value, or your own known-good figure where none is published. Wrong looks like a single touch test and a verdict. Stop rule: on a variable-speed compressor do not use current at all.
Classify against the table below, requiring two agreeing indications. Acceptance: two independent indications pointing the same way, for example a short frost line and current below the plate figure. Wrong looks like one ambiguous reading carrying a compressor verdict. Stop rule: one indication, or two that disagree, means no classification; write that on the ticket rather than guessing.
Hand off, or schedule the re-check. If a non-sealed fault was corrected, restore the machine, state the pull-down time and book the re-check. If the classification stands, hand off to the recovery SOP under Type I certification. Acceptance: a booked re-check with a target and start time, or a recovery record opened. Wrong looks like a system pierced to "confirm with gauges" before anyone decided the repair is happening. Stop rule: no repair authorization, no gauges, because piercing is an opening under 40 CFR 82.156 whatever you find.
What each fault looks like from outside the system
| Family | Suction line at compressor | Evaporator frost | Condenser profile | Current vs plate |
|---|---|---|---|---|
| Low charge or leak | Warm | Frost on the first passes only, then bare | Cool over most of its length | Below |
| Restriction at drier or capillary | Warm | Little to none | Hot at the inlet, cool early; often a cold spot or sweat right at the restriction | Below |
| Condenser airflow restriction, which is not a sealed-system fault | Warm | Weak and uneven | Hot along its whole length and still hot at the drier | At or above |
| Low-efficiency compressor | Close to ambient | Little to none | Only slightly warm | Below |
Head pressure separates the third row from the rest. Restricting condenser airflow raises condensing temperature and therefore the pressure the compressor works against, so current rises. A leak, a restriction upstream of the evaporator, or a compressor that has stopped pumping all cut mass flow, so current falls. A warm cabinet with current below the plate figure is not a condenser story, and one at or above it is not a compressor story.
The record this produces
A sealed-system worksheet attached to the ticket.
- Cabinet: both compartment temperatures with the instrument used, both setpoints, and the complaint's duration.
- Elimination evidence: the frost photograph, defrost heater resistance and terminator state, both fan states, condenser condition, and compressor supply reading.
- Sealed-system profile: the temperature points from step 6 and the current figure with what it was compared against.
- Classification: the family named plus the two indications that agreed.
- Disposition: non-sealed fault corrected with a booked re-check and its target, or a handoff to recovery under a named Type I certified tech.
The next tech reads the elimination evidence before opening anything, which is what stops a second shop entry into the same cabinet. If a replacement recommendation is later disputed, those lines answer "did anyone check the simple things."
One run of this procedure, filled in
Side-by-side, complaint of warm fresh food, about three weeks, freezer "still makes ice but softer."
- Step 1: fresh food 52 F against a 37 F setpoint, freezer 18 F against 0 F. Both compartments warm, which points away from a damper or air-routing fault between them. Pass.
- Step 2: frost present across the evaporator face, even, thin. No ice slab, no bare passes. Pass, and it already argues against both a defrost failure and a low charge.
- Step 3: defrost heater reads within the tech-sheet resistance band, terminator closed at freezer temperature. Pass.
- Step 4: evaporator fan turns at speed. Condenser fan blade turns freely by hand but does not start under a compressor call, and the condenser face passes no light. Fail. Stop rule taken: sealed-system diagnosis stopped here.
- Steps 5 to 7: not run, and that is the point. Run, step 6 would have found a condenser hot along its whole length and current at or above the plate figure, which is the table's third row, not a compressor.
- Step 8: condenser cleaned, fan motor replaced, unit restored. Pull-down stated as 24 hours, re-check booked against 0 F freezer and 37 F fresh food.
- Re-check at 24 hours: freezer 2 F, fresh food 38 F, still falling. Closed as an airflow fault.
The customer's own read was "the compressor is going," and three weeks of warm food with a fresh-food compartment 15 F above setpoint fits that story. What did not fit was the even frost across the evaporator, and that observation cost 3 minutes at step 2.
When the visit cannot run as written
The unit will not run long enough to read. A compressor cycling on overload gives no steady state. Diagnose the overload and start circuit first; a profile taken during a start attempt is meaningless.
Someone has already been inside. A piercing valve on the process tube, fresh solder or a replaced drier says the system was opened. Treat charge-related readings as unknown and say so to the customer.
The plate says R-600a and the compartment smells of gas. Everybody leaves, no switch is touched, no phone is used inside, ventilate from outside, and the unit is not re-energized. This is not a diagnostic step, it is an evacuation.
No Type I certified tech is available. Do not pierce the system to "just check." Book the return with a certified tech and record why.
The cabinet is at setpoint on arrival. Leave a recording thermometer and book a return; a sealed-system fault that is fine on the day is almost always door usage or defrost timing.
References
- 40 CFR Part 82 Subpart F, EPA Section 608: 82.156 recovery requirements and the Type I category for small appliances.
- UL 60335-2-24 for the flammable-refrigerant charge limit applied to household refrigerating appliances.
- 29 CFR 1910.333(b)(2) for electrical work practices; NFPA 70E-2021, 120.5 for the proving sequence.
- Manufacturer tech sheets for defrost values, fan tests and inverter service data.
- See related: the refrigerant recovery on a sealed system SOP, and the repair-versus-replace recommendation standard.