York Heat Pump Not Heating: Diagnosis and Fixes

Common Symptoms

• York heat pump running in heat mode but supply air feels cool or cold
• Outdoor unit running with fan spinning and compressor operating but house temperature dropping
• Thermostat set to HEAT but the system appears to be running in cooling mode
• Defrost cycle running constantly — outdoor coil steaming with no frost clearing
• Aux heat running non-stop while the heat pump appears to contribute nothing
• Outdoor coil completely encased in ice that does not clear after 45–60 minutes
• Heat pump short cycling in heat mode — compressor starts and stops every few minutes
• York YXT communicating thermostat displaying an E-code fault or service alert in heating mode

Most Likely Causes

1. 1

   Reversing Valve Issues — Documented Failure Pattern on Older York Affinity Units

   The reversing valve is a 4-way solenoid-operated refrigerant valve that switches between heating and cooling modes by redirecting refrigerant flow direction. On York heat pumps, the O terminal (orange wire) energizes the solenoid during cooling — the solenoid is de-energized in heating mode and the valve spring-returns to heating position. York Affinity units, particularly those manufactured between 2005 and 2015, have a documented higher-than-average reversing valve issue rate: both solenoid coil failures (coil tests OL) and mechanical spool sticking are more common on early Affinity YZV units than on contemporary Carrier or Trane models. The solenoid coil on York Affinity units reads 8–15Ω when functional. OL confirms coil failure, which is a DIY-accessible repair (replace the solenoid coil without opening the refrigerant circuit). A mechanically stuck valve spool requires an EPA 608-certified technician to evacuate and replace the full valve. York/Johnson Controls reversing valve solenoid coils are interchangeable with Coleman and Luxaire equivalents.

2. 2

   Defrost Board Fault

   The defrost control board monitors the outdoor coil temperature thermistor and a time-based logic circuit to initiate defrost cycles every 30–90 minutes. When the board fails, it most commonly fails in one of two modes: (1) stuck in defrost — the system runs continuously in reverse/cooling mode, the outdoor coil heats and steams without clearing frost, and supply air is cold; (2) defrost never initiates — the outdoor coil progressively builds frost until completely encased in ice, blocking airflow and stopping heat absorption entirely. York Affinity defrost boards share part numbers with Coleman and Luxaire equivalent boards across the Johnson Controls brand family — if a York-branded board is unavailable, order the Coleman or Luxaire equivalent. The defrost board is in the outdoor unit electrical compartment; LED status indicators on the board confirm whether the board is stuck in defrost mode. Always test the coil temperature thermistor resistance before replacing the full defrost board.

3. 3

   Low Refrigerant Charge

   Low refrigerant in heating mode reduces the heat pump's ability to absorb heat from outdoor air. In heating mode, the outdoor coil is the evaporator — low charge causes suction superheat to spike, and the suction line at the outdoor unit feels unusually warm or hot instead of cold and sweating. The liquid line may feel barely cool or ambient temperature. On York Affinity YZV units with a communicating thermostat, a low-pressure fault alert appears in the fault log. On non-communicating YZH units, inadequate heat with no fault codes is the only symptom. Low refrigerant on a York heat pump is almost always due to a leak — common locations include Schrader valve cores on service ports, flare fittings at the service valves, and brazed connections at the indoor coil. R-410A refrigerant recovery and recharge requires EPA 608 certification.

4. 4

   Failed Run Capacitor

   A failed run capacitor prevents the outdoor fan motor or compressor from starting correctly. York Affinity outdoor units use a dual-run capacitor (HERM and FAN sections). A failed FAN section stops the outdoor fan motor, eliminating airflow through the outdoor coil — in heating mode, zero airflow means zero heat absorption from outdoor air. A failed HERM section prevents the compressor from starting, producing a humming outdoor unit with no compression. Test capacitance with a multimeter in capacitance mode: compare measured values to the label rating — a reading more than ±6% outside the rated value confirms failure. Common York Affinity dual-run capacitor ratings: 45+5 μF or 40+5 μF at 370/440 VAC.

5. 5

   Outdoor Fan Motor Failure

   The outdoor fan motor draws heat-exchange air through the outdoor coil during heating and cooling operation. A failed fan motor stops outdoor airflow, preventing heat absorption in heating mode and causing the compressor to short cycle on its high-pressure protection. Test outdoor fan motor winding resistance: disconnect the motor harness, set the multimeter to ohms, and measure between winding terminals (typical York outdoor fan motor winding resistance is 1–10Ω; OL indicates an open winding; near-0Ω indicates a shorted winding). Test each terminal to chassis ground — all should read OL; any reading less than OL indicates a grounded winding requiring motor replacement. Spin the fan blade by hand with power off — it should rotate freely with no grinding or resistance.

6. 6

   Thermostat Wiring Error — O vs B Terminal

   York heat pumps use the O terminal convention: 24VAC on the O wire (orange) energizes the reversing valve solenoid during cooling, and the valve is de-energized in heating mode. If a replacement thermostat is configured for B-type operation, the reversing valve is energized in heating and de-energized in cooling — the heat pump blows cold air in heat mode and heats in cool mode. Verify the thermostat O/B configuration in the installer setup menu. On York YXT communicating thermostats, the reversing valve type is set during equipment configuration. On standard thermostats, look for a DIP switch or O/B selector — it should be set to O for York heat pumps.

Quick DIY Checks

1. 1Step 1 — Thermostat fault check and mode verification: on a York YXT communicating thermostat, navigate to the menu and check stored fault codes or alerts in the diagnostics section — common York heat pump heating fault codes: E1 (high-pressure fault — can indicate stuck reversing valve or blocked outdoor coil) and E2 (low-pressure fault — often low refrigerant charge). Note all active alerts before going outside. Confirm the thermostat is in HEAT mode, fan to AUTO, and the set point is at least 3–5°F above current indoor temperature. Verify the O/B configuration is set to O-type (not B-type) in the thermostat equipment setup. On a standard non-communicating thermostat paired with a York YZH, confirm mode is HEAT and the O/B selector is set to O.
2. 2Step 2 — Inspect outdoor unit for ice and defrost status: walk outside and inspect the outdoor coil. Some coil frost in cold, humid weather is normal. A completely ice-encased outdoor unit with no visible coil fins indicates a defrost system failure. Do NOT chip the ice or pour hot water. Turn the system off or to fan-only mode and allow 2–4 hours for natural melting. After the ice clears, restart in heating mode and watch whether the coil re-ices within 30–60 minutes. If it does, the defrost board or thermistor has failed. If the outdoor coil is continuously steaming without clearing frost, the defrost board may be stuck in defrost mode — open the outer electrical compartment and check the defrost board LED status indicator.
3. 3Step 3 — Test the reversing valve solenoid coil resistance: turn off the outdoor unit at the disconnect box. Locate the reversing valve on the refrigerant circuit — the cylindrical 4-port brass valve near the compressor, with a solenoid coil on top. Disconnect the solenoid coil wire connector (one wire traces to the O terminal on the outdoor control board). Set your multimeter to ohms (Ω) and probe the two solenoid coil terminals. A functional York Affinity reversing valve solenoid reads 8–15Ω — the same specification as Coleman and Luxaire units across the Johnson Controls family. OL (open circuit) confirms coil failure. Solenoid coil replacement is DIY-accessible and does not require opening the refrigerant circuit. If coil resistance is within spec, restore power and test 24VAC at the solenoid connector with the thermostat in COOL mode — should read 24–28VAC. No voltage in cooling mode indicates a thermostat or wiring fault at the O terminal.

1. 4Step 4 — Test the defrost thermistor and assess defrost board: with power off, locate the defrost thermistor — the small NTC sensor clipped to the outdoor coil fins, connected to the defrost board via a two-wire harness. Disconnect the thermistor from the defrost board. Set the multimeter to ohms and measure resistance: at ambient temperature (40–70°F), a functional York defrost thermistor reads 10–50kΩ. OL indicates open-circuit failure; near-0Ω indicates a short. A failed thermistor ($20–$40 part) often resolves apparent defrost board failures on York Affinity units — replace the thermistor before condemning the full board. Note that York, Coleman, and Luxaire defrost boards are interchangeable across the Johnson Controls brand family — if a York-branded board is backordered, order the Coleman or Luxaire equivalent. After replacing the thermistor or board, run in heating mode and verify the defrost cycle initiates and clears the coil within 90 minutes.
2. 5Step 5 — Test the run capacitor capacitance: turn off the outdoor unit at the disconnect. Locate the dual-run capacitor in the outdoor unit electrical compartment. Wait 5 minutes after disconnecting power (or discharge manually with a 10kΩ 5-watt resistor across each terminal pair) before touching the capacitor leads. Set the multimeter to capacitance mode (μF). Measure the FAN terminals and compare to the label rating; measure the HERM terminals and compare. A reading more than ±6% outside the rated value confirms failure. A failed FAN section stops the outdoor fan motor; a failed HERM section prevents the compressor from starting. Common York Affinity capacitor ratings: 45+5 μF or 40+5 μF at 370/440 VAC — match the replacement rating exactly.
3. 6Step 6 — Assess refrigerant charge indicators and outdoor fan motor: with the heat pump running in heat mode, touch the large suction line at the outdoor unit. It should feel cold and slightly moist — distinctly below ambient temperature. An unusually warm or hot suction line with the compressor running indicates low refrigerant charge or a stuck reversing valve. With power off, disconnect the outdoor fan motor harness and test winding resistance: between winding terminals should read 1–10Ω (OL = open winding, near-0Ω = shorted winding); each terminal to chassis ground should read OL (any less = grounded winding). Spin the fan blade by hand — free rotation with no grinding confirms mechanical integrity. If refrigerant indicators are present (warm suction line, oil at Schrader valve cores), stop DIY and call an EPA 608-certified HVAC technician.

Repair vs Replace

Recommended Tools & Parts

• York / Coleman / Luxaire Heat Pump Reversing Valve Solenoid Coil (24VAC)

  Replacement 24VAC reversing valve solenoid coil for York Affinity YZV, YZH, Coleman, and Luxaire heat pump outdoor units (Johnson Controls brand family — parts are interchangeable). Fixes heat pump stuck in cooling mode when the solenoid coil tests OL or out of the 8–15Ω specification. Does not require opening the refrigerant circuit.

  $30–$80

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• York / Coleman Heat Pump Defrost Control Board

  Replacement defrost control board for York Affinity YZV and YZH heat pump outdoor units — also fits Coleman and Luxaire equivalents across the Johnson Controls brand family. Fixes defrost stuck in continuous mode, defrost that never initiates, or a failed status LED. Match the part number from the existing board or the outdoor unit wiring label.

  $80–$200

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• Klein Tools MM400 Digital Multimeter

  Auto-ranging multimeter with capacitance mode — essential for York heat pump diagnosis. Tests reversing valve solenoid coil resistance (8–15Ω spec for York units), capacitor MFD values, defrost thermistor NTC resistance (10–50kΩ range), 24VAC control voltage, and fan motor winding resistance.

  $45–$60

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• Dual-Run Capacitor for York Affinity Heat Pump

  Replacement dual-run capacitor for York Affinity outdoor units — fixes outdoor fan motor or compressor that fails to start or hums without running. Match the capacitance rating (μF) and voltage rating on the original capacitor exactly. Common York Affinity ratings: 45+5 μF or 40+5 μF at 370/440 VAC.

  $20–$60

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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