Lennox THA090 roottop AC compressor not running
 

Hi one of the 2 Lennox THA090 rooftop compressors is not running even though we set the temperature really low. The office still feels warm. We opened the cover and confirmed that one of them is running and the other is not.

However the 2 PCB control boards all seem to indicate everything is fine, based on the LED blink pattern. Any clue? Thanks a lot!

How do we test if the compressor is really broken?

The unit is about 10 years old.

Lennox THA090 roottop AC compressor not running
 

On Thursday, September 3, 2015 at 11:58:33 AM UTC-5, wrote:
Hi one of the 2 Lennox THA090 rooftop compressors is not running even though we set the temperature really low. The office still feels warm. We opened the cover and confirmed that one of them is running and the other is not.

However the 2 PCB control boards all seem to indicate everything is fine, based on the LED blink pattern. Any clue? Thanks a lot!

How do we test if the compressor is really broken?

The unit is about 10 years old.

Simplest way to by-pass everything is to push-in the compressor contactor and see if it kicks-in.

Lennox THA090 roottop AC compressor not running
 

On 9/3/2015 12:58 PM, wrote:
Hi one of the 2 Lennox THA090 rooftop compressors is not running even though we set the temperature really low. The office still feels warm. We opened the cover and confirmed that one of them is running and the other is not.

However the 2 PCB control boards all seem to indicate everything is fine, based on the LED blink pattern. Any clue? Thanks a lot!

How do we test if the compressor is really broken?

The unit is about 10 years old.

The usual. Check for power supply, amp draw.
Disconnect, and check for open circuit, or
short to ground. Check the run cap while you
are in. Nothing challenging, here.

-
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Christopher A. Young
learn more about Jesus
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Lennox THA090 roottop AC compressor not running
 

On Thursday, September 3, 2015 at 11:58:33 AM UTC-5, wrote:
Hi one of the 2 Lennox THA090 rooftop compressors is not running even though we set the temperature really low. The office still feels warm. We opened the cover and confirmed that one of them is running and the other is not..

However the 2 PCB control boards all seem to indicate everything is fine, based on the LED blink pattern. Any clue? Thanks a lot!

How do we test if the compressor is really broken?

The unit is about 10 years old.

In the compressor compartment, there is a blue/green circuit board at top right. On the top left corner of the board you will see, "Y1" and "Y2" which are where the wires from the thermostat that control the staging of the compressors connect. If you don't have a DVM to check the 24vac control voltage, you can disconnect those wires one at a time and see what happens. If disconnecting Y1 which controls the first stage cooling causes the running compressor to stop, it will indicate that circuit is working. Touch the yellow wire that was connected to the Y1 terminal to the Y2 terminal and if the other compressor starts up, it would indicate a problem with either the thermostat or thermostat wiring. Make sure the connections at the thermostat are good which will be the simplest check you can do without test equipment.. I'm guessing you have an electronic thermostat and if the wiring is good, the thermostat could be defective but it's hard to tell without hands on testing. Since it is a heat pump, it could be a bit more complicated to test but the wiring check should indicate the simplest problem you will encounter. ^_^

[8~{} Uncle AC Monster