A/C problem

[Tony Burbank]

Outside unit just hums, dunno what tune.

Put a call in, service tech says it's the capacitor. I seen Back to the Future, and not about to fall for a scam.

Could it be the thermostat or low on freezone?

[Smarty]

The outdoor unit does indeed contain run/start capacitor(s) which would cause the type of problem you are having if it failed.

The recommended replacement of this capacitor is an entirely reasonable suggestion.

(WTF is freezone???)

[RBM]

If he made this determination in person, it sounds reasonable. If he just speculated this over the phone, it is possibly something else. The contactor in the condenser is powered (24 volts) from the thermostat and many contactors hum when energized. The electricity to the condenser motor, which works through the contactor, may be off, or otherwise compromised.

[HeyBub]

It's easy enough to check:

1. Flip breaker or otherwise remove power.
2. Open business side of compressor unit.
3. Find capacitor(s). They look like small aluminum cans with wire plugged on.
4. Take picture of wires and mark on chassis.
5. Remove capacitor(s).
6. Take to Graingers and say "Gimme some like this" (about ten bucks).
7. Install new.

[clare]

A thousand things are possible - but of them, only one is probable. Start with the capacitor, or hire someone to come in and make a definitive diagnosis.Which will LIKELY be the capacitor.

[RBM]

Instead of just throwing parts at it, how about first check to see if you have power to the unit?

[clare]

Like I said - a thousand things are possible - only one is PROBABLE in this case. The OP says the outer unit hums. If it was just the contactor it would barely buzz.

[DD_BobK]

Freon?

[larry moe 'n curly]

Did the tech apply 1.21 jigawatts, as Doc Brown says it needs to work?