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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 852
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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I have 2 year old carrier 2 ton units (2) outside my house

Customer Question

I have 2 year old carrier 2 ton units (2) outside my house that won't come on. The inside blowers and thermostats work. The AC tech came out and determined that the electric sub panel serving the outside units was bad since it was deteriorated and old. The voltage he said dropped almost completely whte the unit switch tried to engage
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: we changed out the electric sub panel and put all new breakers in it as well as replaced the breaker at themain panel feeding the sub box. still the outside units will not come on
JA: Do you plan on doing the work yourself?
Customer: I'm waiting on the AC company to return
JA: Anything else we should know to help you best?
Customer: I have wired residential and commercial property in the past, so I understand electricity pretty well, but have little understanding of the AC specific. was thinking maybe its a problem specific to Carrier
Submitted: 5 months ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 5 months ago.

Hi I'm Brian and I'm here to help!

You may want to try turning off power to the indoor units to interrupt the low voltage system and possibly 'reset' any trouble the line voltage issue may have caused. If the Carrier units are higher end, like an Infinity system, they may be locked out and cycling power to the indoor units should reset them.

If you confirmed line voltage supply to your condensing units, which it sounds like you did, then the problem will be in the 24 volt signal to them or possibly a problem within them such as burnt up contactors from the low supply voltage and degraded electrical branch circuit system. If you turn the thermostats off then back on, and have a helper stand by the units, if your helper hears an audible "click" when the ac units are called to run, that tells you the low voltage control signal is getting to the units. If the click is not heard then the problem could be in the low voltage signal that should be sent outside but is not do to thermostat issues or drain line switch issues. If the signal is making it outside whether you hear the click or not, then there is a problem within the outdoor units like a contactor, time delay relay or unit safety control (high or low pressure cutout or the like).

If you have a volt meter and would like help using it to diagnose the exact problem, I can help with that if you'd like. I would need model numbers of the outdoor units to help with that.

Let me know if you have further questions on this subject. Otherwise, please remember to rate before leaving (3 stars or higher please!). Bonuses are always appreciated! And remember, follow up questions about this topic are free even after rating. Just post a new reply on this same question and I'll be notified. Thanks for allowing me to help and thanks for using Just Answer!

Thank you,