Blower delay on Trane package unit

[ih784]

Hello, I have a Trane package unit. I think I have an issue with. The fan on top of the unit comes on 30 seconds or a minute before the blower comes on and starts to push air through the vents. This only happens 1 out of 10 times of the heat pump coming on. A 15 microfarad capacitor was metered to 13 microfarads and replaced with a known good (15 microfarad) capacitor. Is it normal for the fan to run before the blower motor turns on?

 

[Jadnashua]

What kind of unit is it? Heat pump? Gas fired furnace? What? What is the fan designed to do? FWIW, the cap was probably fine...some of them are rated at +/- 20% or more of nominal.

In most furnaces, the blower motor is controlled by a sensor that is used to detect the heat exchanger temperature. It doesn't turn on until the heat exchanger is warm so you don't get cold air, then keeps running until that cools off after the burner stops.

On a heat pump, a similar thing...it waits until things are warm before turning on the blower. The compressor would have to run for a bit before it was generating any heat.

 

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[ih784]

What kind of unit is it? Heat pump? Gas fired furnace? What? What is the fan designed to do? FWIW, the cap was probably fine...some of them are rated at +/- 20% or more of nominal.

In most furnaces, the blower motor is controlled by a sensor that is used to detect the heat exchanger temperature. It doesn't turn on until the heat exchanger is warm so you don't get cold air, then keeps running until that cools off after the burner stops.

On a heat pump, a similar thing...it waits until things are warm before turning on the blower. The compressor would have to run for a bit before it was generating any heat.

The model number is 4wcc3036a1000ab. It is a heat pump and what you said makes perfect sense to me. It could've been preforming this way it's entire life and I just haven't noticed it. I was concerned since 90% of the time they both come on together. What you described would explain it. I suppose there is a sensor or separate control telling it to build heat to a certain degree before the blower comes on?

 

[Jadnashua]

It appears that the outdoor fan comes on at the same time as the compressor. SO, during a call for heat (assuming it isn't too cold and it won't run the compressor), the compressor turns on, the fan comes on, and once it starts to generate heat, the indoor blower fan comes on. There would normally be at least a small delay between the compressor starting and heat generation. IOW, if I had to guess, it sounds normal.