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Residential HVAC

I have a Trane heat pump, model number XP14-024-230, and the homeowner heard the unit make a crazy…

Discussion · Sep 18, 2026

I have a Trane heat pump, model number XP14-024-230, and the homeowner heard the unit make a crazy noise when it came on that sounded like fireworks. The contactor was being pulled in and then released and repeated very rapidly. The contacts were very toasty so I replaced the contactor with an exact replacement according to the ratings. The unit worked as it should but then after it ran for a while and satisfied the thermostat and then was called to come on again, it did the same thing. If you let it sit for an hour and then turn it on, it runs fine. All the voltages from the defrost board are correct and nothing else seems to be abnormal. Anyone have anything like this before?

Replies

Reply · Sep 18, 2026

What type of thermostat are they using? The reason I ask is because we have run into installation issues with Trane rooftop units acting up similarly to what your unit is doing with mercury thermostats. It's almost like these new boards do not like mercury thermostats, so every time we run into a mercury thermostat, we replace it.

Reply · Sep 22, 2026

I think you mean Lennox heat pump by the model number you gave. It sounds like a low voltage back feeding issue. I'd isolate the low voltage from the heat pump, the air handler and thermostat. Test each component individually to see if the sound returns. I've seen Lennox defrost boards short out and take out other components. In addition the thermostat also can back feed if its not powered by the 24v and short out components.