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Discussion Starter · #1 ·
I had this issue with my previous old unit and this one that was installed approx 3 years ago.

This is a heatpump system and I have the issue in heat or cool mode and have replaced the thermostat.

Randomly the outside unit will not power on (or shuts off while running, not sure which). I discover the issue because the fan is running without it getting any warmer (in winter) or cooler (in summer). I have 2 double breakers for the system and neither will be tripped. I can turn off the thermostat and both breakers for a couple mins, then turn them both back on and set the thermostat and it works again.

Some research I have done may indicate I need a hard start capacitor. Or, that the the system may be overheating due to not enough airflow due to closed off vents etc.

I do have a couple vents closed off but seem to have a lot of airflow through the many other vents I have. Filter is changed regularly. One other thing of note is that my house is about 40 years old and on a slab. One company that I got a quote for when replacing the unit mentioned that they may need to run new tubing through the attic as the tubing going through the slab is too small for a modern system. The company that ended up replacing it didn't think it was an issue but did have to use a reducer on the lines.

So, I am thinking of replacing the breakers for good measure and then consider a hard start cap (they are cheap enough). Other than that, any suggestions on what the cause is or how to try to track down the cause?

Thanks
 

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Do not replace any parts until troubleshooting is done.
It sounds as if the unit is shutting off on a diagnostic code.
Next time it shuts down open the panel and see if there’s a code. Check for an active call with your meter.
What’s the model number of the unit?
 

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Discussion Starter · #3 · (Edited)
The air handler is a lennox CBX25UH-030 and the external unit a 14HPX-030-230.

Do you mean look at the board on the external unit for a code on the diagnostic leds?

It just seems strange that I am having the same issue with the new unit that the old unit had. This is why I am thinking of a power or tubing restriction issue. BTW, it wasn't replaced for this issue. The compressor failed on the old unit. It was really old BTW. Like 25 years or so.
 

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Check for an active call to the outdoor unit.
Could be a condensate protection device, a power conservation device or something else.
But still, don’t start replacing random parts. Breakers and compressor starting components can be easily tested with your meter.
 

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Discussion Starter · #5 ·
Thanks but not familiar with the term "active call" and my google-fu hasn't helped :) I assume you mean look at the diagnostic LEDS?
 

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Discussion Starter · #9 ·
So It happened yesterday. Had power at the outside unit and the diagnostic LEDs indicated "High Pressure Switch Lockout". I have read up on the possible causes and nothing jumps out. I plan on cleaning the outside coils (the unit has plenty of open area, nothing blocking airflow) and checking the vent tubes in the attic to make sure there are none that are collapsed and will open up a couple vents I have closed. I will also test the start capacitor. Filter is changed regularly.

Any other suggestions?
 

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High pressure switch lockout means a problem on the indoor coil in heating mode, the outdoor coil in cooling mode.
Is the indoor coil clean? Blower running properly? Blower wheel clean?
Honestly you may want to get someone out to check operating pressures.
 

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Discussion Starter · #11 ·
Ok, so is the cause the fact that there is not enough heat transferred from the refrigerant before it goes back to the outside unit? Like not enough airflow (dirty coils, slow fan speed etc?)
 
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