Heat Pump Troubleshooting Guide for BC

How BC's Climate Changes the Diagnostic Picture

BC's HVAC landscape is genuinely different from central Canada. Kelowna winters hit -15 to -20°C regularly. The Fraser Valley and coast are milder but extremely humid — the kind of wet cold that frosts outdoor coils faster than dry prairie air. Vancouver Island can swing from 0°C fog to 30°C+ heat in the same season.

Cold-climate heat pumps from Mitsubishi, Daikin, and Fujitsu are rated to -25°C and lower. But standard heat pumps — installed under the older BC Hydro programs — lose meaningful capacity below -8°C and need auxiliary heat to keep up. Know what you're walking into before you arrive.

FortisBC rebates (up to $4,000 for a standard heat pump, $12,000 for income-qualified households) have driven huge adoption. Many of these units are 1–3 years old. Warranty coverage is often still active — confirm before you replace anything.

Defrost Cycle — Normal vs. Problem

The defrost cycle is the most misunderstood thing about heat pumps. Customers panic when they see steam coming off the outdoor unit or the system apparently "blowing cold air" for a few minutes. This is normal.

During defrost, the reversing valve switches to cooling mode to push hot refrigerant through the outdoor coil and melt the frost. The outdoor fan stops. Indoor air may feel slightly cool. The process takes 5–10 minutes, then the unit returns to heat mode.

Normal defrost: The outdoor unit has light frost on the coils in cold/humid conditions. The unit defrosts every 30–90 minutes (varies by board logic and outdoor conditions). After defrost, heating resumes fully.

Problem defrost: The outdoor unit is encased in ice — not just frost. The unit runs in defrost but the ice doesn't clear. Or defrost never triggers and ice builds up continuously.

1. 1
   Check the defrost sensor (thermistor)

   This probe on the outdoor coil triggers defrost when it detects the coil is near freezing. If it fails low (reads too cold), defrost runs constantly. If it fails high (reads too warm), defrost never runs and the coil ices over. Test resistance vs. temperature using the OEM chart.
2. 2
   Check the defrost board/timer

   Older units use a timer-based defrost board. If the board is stuck, defrost either never runs or runs continuously. Check for power to the board and test relay operation.
3. 3
   Check for low refrigerant

   Low charge causes suction temperature to drop below normal, which accelerates ice buildup on the outdoor coil. If you're seeing icing beyond what the defrost cycle can handle, check your pressures.

Not Heating Well in Cold Weather

This is the most common complaint in an interior BC winter and it has several possible causes — some normal, some requiring service.

First, check the outdoor temperature. Every heat pump has a published balance point — the outdoor temperature at which it can no longer meet the heating load on its own and auxiliary heat must supplement. A standard heat pump might balance at -5°C. A Mitsubishi H2i might balance at -18°C. If it's colder than the balance point and the backup heat is working, the system is behaving correctly.

If the temperature is within the unit's operating range and it's still not keeping up, suspect: dirty air filter, dirty indoor coil, low refrigerant, or a malfunctioning reversing valve.

Reversing Valve Diagnostics

The reversing valve switches refrigerant flow direction to change between heating and cooling mode. When it sticks, you get heat in cool mode or cooling in heat mode — a very confused customer.

Most heat pumps are wired so the reversing valve is energized in cooling mode and de-energized (spring-loaded) in heating mode. Confirm your brand's wiring diagram before testing.

To test: in heat mode, measure for 24V at the reversing valve coil terminals. There should be no voltage if energized-in-cooling wiring is used. If 24V is present when it shouldn't be, the thermostat or control board is sending the wrong signal.

If wiring is correct and the valve still won't shift, tap the valve body firmly with the handle of a screwdriver while the system is running. Sometimes a stuck slide will break free. If it won't budge, replacement is required.

Capacitor and Compressor Checks

The outdoor unit on a heat pump has the same electrical failure points as a central AC: run capacitor, start capacitor (on some units), contactor, and the compressor itself.

A failed capacitor is the most common reason a heat pump compressor or outdoor fan won't start. It's also the cheapest fix. Always test capacitance with a dedicated tester — a multimeter's resistance check is not reliable. Compare your reading to the nameplate µF ± 6%.

If the capacitor tests good and the compressor won't start, check the contactor: are the contacts burned or pitted? Is there 24V to the coil when it should be energized? Are the contacts pulling in?

For compressor diagnosis: measure amp draw against nameplate RLA. A compressor drawing far above RLA is under mechanical stress. A compressor drawing no amps with contactor closed and correct voltage present has an open winding — confirm with an ohmmeter across each winding pair.

Mini-Split Error Codes (Mitsubishi, Daikin, Fujitsu)

BC has a huge installed base of mini-splits, particularly in homes without ductwork. Error codes are your fastest path to a diagnosis.

Mitsubishi uses a flashing LED system on the indoor unit. Count the short blinks before the pause, then the long blinks after. The combination gives you the error code — look it up in the service manual or the MSZ series error code chart.

Daikin displays alphanumeric codes on the remote or indoor unit display. Common codes: A1 (indoor PCB fault), C4 (indoor coil sensor), E1 (outdoor PCB), H6 (outdoor fan motor fault), F3 (discharge temp high).

Fujitsu shows codes on the operation lamp flash pattern on the indoor unit. The remote sometimes displays a code number directly if it's a wired remote.