Trane Heat Pump Not Cooling: Causes, Fixes & Costs

Last updated Oct 5, 2026 · By fixme.vip Editorial

Trane heat pump not cooling: what it means

“Not cooling” isn’t a single flashing code. It describes a Trane heat pump that runs, or tries to run, in cooling mode but doesn’t bring the indoor temperature down. A heat pump cools by pumping heat out of the house through the outdoor unit. Anything that stops the outdoor compressor, starves the system of refrigerant or airflow, or leaves the reversing valve in heating position will cause it.

How Trane systems report this depends on the model:

• Single-stage and two-stage units (XR, XL, and most Value/Comfort models) usually show no code at all. The unit simply runs warm.
• Units with a defrost or pressure board may show LED flashes for high-pressure or low-pressure trips. On many boards, pressure trips reset automatically after a delay. Some lock out after repeated trips until you cycle power.
• Communicating variable-speed systems (XV18/XV20i with ComfortLink II) log specific fault codes on the thermostat. If yours does, give that code to your technician.

This page covers cooling mode only. For heating failures, see Trane Heat Pump Not Heating.

Trane heat pump not cooling: common causes, ranked by probability

1. Thermostat setting or power problem. The thermostat isn’t set to Cool, the setpoint is above room temperature, the batteries are dead, or the outdoor unit’s breaker or disconnect is off.
2. Dirty air filter or blocked airflow. Restricted airflow drops coil temperature, the indoor coil freezes, and cooling stops.
3. Failed run capacitor. This is the most common outdoor-unit failure in hot weather. The compressor and/or outdoor fan hums but won’t start.
4. Failed or pitted contactor, or no 24V call reaching the outdoor unit. The indoor fan runs, but the outdoor unit stays silent.
5. Low refrigerant from a leak. The unit runs constantly, the lines or indoor coil ice over, and supply air is only slightly cool.
6. Dirty outdoor coil or failed outdoor fan motor. Heat can’t be rejected outside, so the high-pressure switch trips, often on the hottest afternoons.
7. Reversing valve or solenoid fault. The valve stays in heating position, so the unit blows warm air in Cool mode. Trane heat pumps energize the valve (O terminal) for cooling, so a failed solenoid coil or wiring fault produces exactly this symptom.
8. Clogged condensate drain tripping a float switch. The float switch cuts the cooling call if one is installed.
9. Compressor failure. This is the least common cause but the most expensive.

How to fix Trane heat pump not cooling: safe checks first

• Thermostat: Set it to Cool with the setpoint at least 3°F below room temperature and the fan on Auto. Replace the batteries if the display is dim or blank. Wait 5 minutes, since many Trane units have a built-in compressor delay.
• Breakers and disconnect: Check that both the indoor air handler or furnace breaker and the outdoor unit’s double-pole breaker are on. Confirm the outdoor disconnect next to the unit is fully seated or switched on. Reset a tripped breaker once only. If it trips again, stop and call a technician.
• Air filter: Replace it if it’s dirty. A clogged filter is a leading cause of a frozen coil.
• Ice: If you see ice on the copper lines or indoor coil, set the thermostat to Off and the fan to On until it fully melts. Don’t chip at the ice.
• Vents and registers: Open the supply registers and clear furniture away from return grilles.
• Outdoor unit, from the outside only: Clear leaves, grass clippings and debris from around the unit. Keep 2 feet of clearance. You can gently hose off the fins from the outside with the power off at the disconnect. Don’t open the unit’s panels.
• Condensate line: If the drain pan is full or the float switch has tripped, clear the drain line opening with a wet/dry vacuum at the outside end. Make sure all access panels on the indoor unit are seated.
• One reset: If the unit seems locked out, cycle power off for 5 minutes at the breakers, then restore it one time. If it doesn’t cool afterward, call for service.

How a technician will diagnose it

A competent tech will typically:

1. Verify the thermostat call. They measure 24V at Y, and at O for the reversing valve, at the outdoor unit, and check for any stored fault codes on the board or communicating thermostat.
2. Check high voltage at the contactor and inspect the contacts for pitting.
3. Test the run capacitor’s microfarad rating against its label. A reading more than about 6% low is a common replacement threshold.
4. Measure compressor and fan motor amp draw and compressor winding resistance.
5. Connect gauges and measure suction and liquid pressures, superheat and subcooling, and compare them against the Trane charging chart on the unit’s panel.
6. Check the temperature split across the indoor coil (typically 16–22°F) and the static pressure and airflow.
7. If refrigerant is low, leak-search with an electronic detector, bubbles or a nitrogen pressure test. A good tech won’t just “top off” the system without discussing the leak.
8. Verify reversing valve operation by checking line temperatures and solenoid coil voltage and resistance.

Red flags in a quote: a compressor condemned without winding and amp tests, repeated refrigerant top-offs with no leak search, or a full system replacement quoted for a capacitor-type symptom.

Symptom, cause and what to do

Trane heat pump not cooling repair cost

Typical US installed prices, including parts and labor:

Older systems using R-22 refrigerant cost much more to recharge, and major repairs on them often make replacement the better value. Check your Trane registration status, since many units carry a 10–12 year limited parts warranty.

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