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Ask Hank F. Your Own Question
Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14560
Experience:  Certified on Onan and Generac generators
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My 20kw generac started today when a power line was cut. The

Customer Question

My 20kw generac started today when a power line was cut. The power however didn't come on. I found the 65amp breaker tripped inside the cabinet. I reset the breaker and the lights and recipticles were live but the 5 ton air conditioning unit would not run. The condensing fan motor ran but the compressor wouldn't come on. It would attempt to and I could hear the load on the generator then the compressor would stop and the generator speed would pick back up. Any ideas as to why it would not power up my air conditioning unit?
Submitted: 1 year ago.
Category: Small Engine
Expert:  Hank F. replied 1 year ago.
There are many reasons that the genset might not power up the A/C - and not all of them are because of the generator. When an A/C unit is running, one side of the system develops very high pressure. If the unit is shut off and turned back on too quickly, high head pressure can prevent the compressor from being able to start. This is why you need to wait for a few minutes after shutting off an A/C unit before trying to restart it - to allow that pressure to dissipate. Your A/C unit may also be going bad - although if it was working properly from utility, that is probably not the case. As far as the genset, there are a few reasons it might not power the A/C:Voltage output is too lowRestricted fuel supplyBad governor or control (depending on what model you actually have)
Customer: replied 1 year ago.
The ac unit is good and the delay between starting it up after utility outage was 20 min. Also when plugging in a hair dryer the lights actually dimmed. What would cause this ?
Expert:  Hank F. replied 1 year ago.
That would most likely be a voltage issue from the genset - the voltage is too low.
Customer: replied 1 year ago.
What would cause that low voltage issue
Expert:  Hank F. replied 1 year ago.
Without testing, or knowing which model of genset you have, it is hard to say.But common causes would be bad voltage regulator (if your unit has one), bad controller (if your unit is a newer model), bad brushes, dirty slip rings, or possibly a bad stator.