Why does outside a/c unit continue to run and inside shuts off?

Question

My A/C unit outside continues running even though the air handler inside shuts off, thus freezing the pipes and potentially causing serious damage. When the thermostat is switched from automatic to manual the inside fan comes back on. Does this seem like a thermostat problem or a/c problem? The thermostat was replaced 3.5 years ago and is a mercury style.

Answer 1

The furnace fan should contiue to run for as long as the compressor unit (outside) runs. If the furnace fan shuts off, the cause needs to be determined.

The problem can be something is turning off the power to the blower motor, or the blower motor itself could be kicking off because it perceives a temperature overload.

I suggest that you determine if there is voltage to the motor when it stops but should not be stopped. This is a bit more complex because the outer door in most furnaces have a shut off switch that will also turn off the motor. I once connected volt meter leads to a pair of wires I fed through a wire duct into the blower area and connected the pair to the motor power. I monitered the volt meter when the fan stopped when it should not stop.

If the voltage to the motor is still on and the motor stops, the motor has stopped for some reason and replacement is in order. If the voltage to the motor goes off, then we need to determine why and resolve that.

My first guess is the motor itself but check that out to be sure.

As always, be careful when measuring voltages; you are at the voltage level where an error can be fatal.

Write with a new question if the motor is not the fault.

Answer 2

Either its wired wrong,or the t-stat is bad.Also could be a stuck contacter on condenser.When your t-stat reaches your desired tempature,its supposed to cut power to the y leg on the condenser which controls cooling,in laymens terms the condenser should shut off when the temp is reached in your house.The y leg goes from your t-stat straight to the condenser and has nothing to do with the air-handler.So its one of the three things i said.If you had a electrical meter it could be diagnosed easily,its also an inexpensive problem,which is good for you.My guess from here is bad t-stat.

Answer 3

Alot of folk have no theory this; for each 5 ranges above 95, your technique loses 15% of it cooling potential. i ask your self if your neighbor has western dealing with outer partitions... the only diverse danger i'm thinking is that the setting up team did no longer properly evacuate and fee the line set. (some truly do whats noted as a purge)

Answer 4

go digital, replace thermo, then look at the air handler for reasons for fan to shut off. you have a troubleshoot problem, requires a person to be there to troubleshoot.

Answer 5

sounds like the relay on the condensor is stuck or the thermostat is bad or wired wrong

Answer 6

im wiith paul.. but a good slap on the ac unit might turn it off.. then you'll know.. also if its a newer furnace with a circuit board.. it could be bad also.