VCC® Compressor – Technician Training & Diagnostic Guide
Internal training reference for Advance Appliance Ltd technicians. This guide explains how VCC (Variable Capacity) compressors work, how speed is controlled, and how to safely diagnose compressor, inverter, and control faults.
How the VCC Compressor Works
A VCC (Variable Capacity Compressor) is controlled by a frequency (inverter) control board mounted next to and wired to the compressor. The VCC runs at various speeds depending on the thermal load in the refrigerator and the ambient temperature.
- Stabilizes cabinet temperature faster than a conventional ON/OFF compressor.
- Uses less electricity than a conventional compressor of the same size.
- Does not go through a high-amperage hard start like a relay-driven unit.
- Compressor speed is controlled via the ambient air NTC (thermistor).
The starting speed and subsequent speed increases depend on the ambient temperature registered by the NTC and the total compressor runtime.
Compressor RPM by Ambient Temperature (Normal Operation)
First speed increase: after ~80 minutes of continuous operation (or ~60 minutes after defrost) the compressor increases by ~600 rpm. Second increase: after a further ~30 minutes, another ~800 rpm. Speed is not reduced while the compressor is running.
Frequency & Speed Control (Inverter Output)
The power electronic (inverter) uses discrete output frequencies to control compressor speed. Each frequency corresponds to a specific rpm and cooling capacity.
| Frequency (Hz) | Speed (rpm) | Typical Use |
|---|---|---|
| 53.3 Hz | 1600 rpm | Low cooling demand / energy-saving mode |
| 73.3 Hz | 3600 rpm | High cooling demand / Super mode |
| 100.0 Hz | 3000 rpm | Normal operation at warmer ambient |
| 116.7 Hz | 3500 rpm | High ambient / heavy load |
Higher frequency = higher rpm = more cooling. The system may also default to ~3000 rpm if the ambient air NTC is defective (failsafe behavior).
Compressor Coil Testing (VCC Motor Health)
These tests are done with power off. They confirm if the three-phase compressor motor windings are electrically healthy before further control or inverter diagnosis.
Three Coils on Compressor – Resistance & Ground Check
1. Coil-to-Coil Resistance
- Label the compressor terminals U, V, and W (three-phase).
-
Measure resistance between:
- U–V
- V–W
- U–W
- All readings should be approximately the same.
- Reference value: ~16 Ω ±0.5 Ω at 75 °F (24 °C).
Small variations due to temperature are acceptable as long as all three readings are equal. If one reading is significantly higher or lower than the others, the winding is likely defective.
2. Coil-to-Ground Test
- Measure from U → Ground, V → Ground, W → Ground.
- There should be no continuity to ground (meter reads OL / Infinite).
| Test Result | Interpretation | Action |
|---|---|---|
| All three readings ≈16 Ω, equal | Healthy windings | Proceed to wiring & control tests |
| One reading much lower | Shorted turn / short-circuited coil | Replace compressor (sealed-system repair) |
| One reading much higher | Open winding / interruption | Replace compressor (sealed-system repair) |
| Any coil to ground continuity | Grounded compressor | Replace compressor (sealed-system repair) |
Wiring, VCC Controls & Non-Start Diagnosis
If the compressor windings test correctly, the next steps are to verify wiring from the control to the compressor, test alternate control modules, and determine if the compressor is seized.
1. Wiring From VCC2 Control to Compressor
If correct resistance values are measured on the compressor, check for continuity in the leads from the VCC2 control module to the compressor.
- Check all three motor leads (U, V, W).
- Inspect harnesses and connectors for breaks, corrosion, or heat damage.
- If any leads or connectors are broken, repair or replace them.
2. VCC2 to VCC3 Control Swap Test
If all leads and connectors are in order and the compressor still does not run, remove the VCC2 control and replace it temporarily with a VCC3 control.
- VCC3 controls do not have a speed-control connection.
- Power the appliance with the VCC3 installed.
- The compressor should start after approximately 90 seconds.
| VCC3 Test Result | Interpretation | Next Step |
|---|---|---|
| Compressor starts after ~90 s | Compressor & wiring OK, VCC2/control signal suspect | Proceed to VCC Control Testing (speed-signal voltage) |
| Compressor does not start | Possible seized compressor or inverter fault | Evaluate inverter output; likely sealed-system compressor replacement |
3. Compressor Non-Start & Seized Condition
If the compressor does not start after approximately 2 minutes of receiving a valid start command and correct inverter output, the compressor is considered seized.
- Internal mechanical components are locked and cannot rotate.
- Even if windings test good, the rotor/pump assembly may be mechanically stuck.
- A sealed-system repair will be required to replace the compressor.
VCC Control Voltage & Speed-Signal Testing
These tests confirm that the VCC control is powered correctly and that the power electronic is sending the correct DC speed-control signal.
1. Line Voltage to VCC Control – Supply Check
Step A – Check at Terminal Block
- With the appliance connected to power and switched ON, measure voltage at the main terminal block.
- There should be approximately 120VAC going to the appliance/VCC control.
- If there is no voltage, check the wall outlet, breaker, and any GFCI/AFCI devices.
Step B – Check at VCC Control Input
- Test for voltage (~120VAC) directly at the VCC control power input.
- If 120VAC is at the terminal block but not at the VCC control, there is a wiring/harness issue.
- If 120VAC is at the VCC control input and it does not power up/respond, the VCC control is likely defective.
| Test Location | Reading | Diagnosis |
|---|---|---|
| Terminal block | ~120VAC | Household supply OK |
| Terminal block | 0VAC | Outlet / breaker / supply issue |
| VCC control input | 0VAC but 120VAC at block | Wiring / harness fault to VCC control |
| VCC control input | 120VAC but no operation | Faulty VCC control module |
2. VCC Control Speed-Signal Voltage Check
With the VCC3 control still in the appliance, check the voltage at the speed-control connector (reference: Fig. 61, Item 2) while the appliance is turned ON.
- Use a DC voltmeter.
- Measure the DC signal voltage at the speed-control connection.
| Measured DC Voltage | Interpretation | Action |
|---|---|---|
| Between 1 and 10 VDC | Power electronic is sending a valid speed-control signal. | Install a new VCC2 control (with speed-control connection). |
| 0 VDC | No speed-control signal being sent. | Replace the power electronic and reinstall the original VCC2 control. |
| Above 10 VDC | Invalid / out-of-range signal from power electronic. | Replace the power electronic and reinstall the original VCC2 control. |
Summary: If the speed-signal voltage is 1–10 VDC, the inverter is good and the VCC2 control is suspect. If the speed-signal voltage is 0 VDC or >10 VDC, the inverter (power electronic) is faulty and must be replaced.