hvac Tech.

Errrrmmm if you have no power for the contactor, how is the motor going to start?

John.

cummings, I was not being insulting at all.... it was a genuine query!!!

How could he start a motor without any power?

That is a good question that immediately struck me when reading his question!!

The only thing insulting about it is your childish response

OK, so assuming there is no power to the control circuit for whatever reason though there is 3ø power to the motor, then, yes, it can be done though practically for testing purposes only.

<Caution>

The door interlock with the mains isolator will need to be over-ridden for this to happen in most cases, which will make the power terminals upstream of the contactor live.

Bumping the contactor will also make the motor terminals live for the duration the contactor is held in, which is an unusual situation from a safety point of view.

• Make sure that no-one can come into contact with the live terminals during this event!
• Be bold and push the contactor firmly, as it is hand pressure that will be holding the contactor closed against its return spring rather than the usual electromagnet. Some sort of push-stick may be preferable to using a finger?
• "If in doubt, get out."

</Caution>

<Caution>

Further, bear in mind that any emergency stop button local to the motor will be inoperative during the test period.

</Caution>

i feel you'd know the answer to this if you were an hvac tech. regardless - yes, you can operate a fan/compressor motors by manually working the contactor providing the proper high voltage is present at the contactor (additionally - assuming the contactor has good contacts, assuming the capacitor(s) is(are) working properly, assuming the wiring is good, assuming the motors aren't bad and, in the compressors case, assuming it's thermal overload isn't open at the time you do this.