Fan A/C compressor

Specific Inspection Topics Inspecting HVAC Systems
1

What would cause the fan to stop and the compressor to keep running on a split system unit, fan would start back up after a few minutes, thermal trip on the fan motor?

2

Not sure Jeff, but at least you had A/C today as mine was not hooked up the last two jobs and it was the same developer.
Sounds like an electronics issue

3

You sure you didn’t catch it while in defrost mode?

4

No, Did it several times during inspection, home owner says-its been like that for a few months, something is messed up. It’s a Heil unit 7-years old.

5

What no A/C !!!

6

No AC and un vented attics.
Tried to find serial number for the NCP but no luck.
Often they are the original when I have seen them.

7

Is it an older unit? Fan/limit control switch?

8

Indoor fan or out door fan?

9

He said split system so the compressor fan would be outdoors.

10

He didn’t say compressor fan, just fan.

11

Run capacitor

12

Unvented attics?

13

Outside fan at compressor. indoor side ran fine.

14

Don’t they just go bad?

15

yep,metal roof over the vent holes down in cal city.Maybe Charlie will know Jeff, but I just tell them to repair.

16

You have two choices, electrical and mechanical.

It’s very difficult to diagnose HVAC issues when home inspectors diagnose equipment failure through observation and cannot take additional measurements because it’s outside the scope of the inspection.

A fan limit switch is something on a furnace, not an air conditioner. When in the air-conditioning mode, the fan/limit control switch is bypassed out of the circuit. The fan is controlled through the yellow thermostat wire rather than the white wire.

If the capacitor was bad it wouldn’t start without turning it by hand first.

There is a possibility that it is going through a defrost mode (because of closed “normally open” sensors), but highly unlikely.

It is also unlikely (but possible because you’re in Chicago) that there is a low ambient kit installed on the unit and low refrigerant pressure is cycling the condenser fan motor to keep the pressure up.

Electrical:

Fan motors have internal overload protection inside their windings.

  1. Electrical components of the motor will get hot because of excessive resistance on the motor causing an increase in amperage draw. This would be associated with a mechanical condition such as a bad bearing/bushing.
  2. As motors fail, sometimes the insulation on the motor windings will short out on the same phase which basically shortens the length of the motor winding wire. This increases amperage draw and heat which will cycle the limit switch.
  3. A loose electrical connection could cause an imbalance of electrical power causing the motor to heat up.
  4. Sometimes the overload protection device goes bad and simply shuts off at a lower temperature.
  5. The fan relay could also drop out because it’s overheating.
    Conducting an amperage test on the primary run winding will answer these questions. Do you have an amperage reading?

Mechanical:

  1. As noted in electrical, bad bearings or bushings will cause a load against the motor causing increased amperage draw and increased heat.
  2. Some condenser motors are open cased and are air cooled. They have a rain cap on the top of the motor and they are open at the bottom. Restricted airflow will cycle the motor (unlikely condition).
  3. Bad motor bushings. The motor is mounted in the vertical position and the fan blade causes a downward force on the motor shaft. Sometimes the motor bushing can go bad and the Armature slips out of the electromagnetic field causing motor to draw excessive amperage resulting in heat.

These are a couple of considerations that passes through the HVAC contractor’s mind as he approaches the situation. As you can see, it is not cut and dry even with a very simple component like a motor.

17

Thanks, I recommended HVAC Tech, just wanted to know for my own educational moment.