This unit is in an apartment building in NYC. Each room's unit is self
contained (not central heat/air).
I was not able to find any low voltage controls inside of the unit. There is
a wiring diagram I could post a link to if anyone thinks that would help.
I thought about wiring into the thermostat, but this would leave the fan
"Byron A Jeff" <byron@xxxxxxxxxxxxx> wrote in message
> In article <SmVfg.5082$ci.2432@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
> HS <N@xxxxxxxxxx> wrote:
> >I want to be able to switch an HVAC unit on/off. The unit is 220V AC.
> >the compressor on the unit draws about 8 amps.
> There's no need for additional circuitry for this operation.
> >Because of the high voltage/current I want to make sure that this is
> >completely safe.
> So the best thing to do is not add any addition circuitry for this
> >1. Is this project a bad idea in general,
> > or is switching through the relay a safe way to turn AC/heat on and off
> > (rest of circuit will be optically isolated)
> Not the way that you're proposing to do it.
> >2. Assuming that I don't toggle power too often, is this switching method
> >'bad' for the AC unit (eg. for the AC give it several minutes before
> >it on again, if it has just been turned off)
> AC works better when it runs longer. That's why it's a bad idea to
> The cycle times become too short.
> >3. If I use a relay rated at 220V 10A will that be sufficient?
> >4. Can anyone recommend a relay with above specs (coil DC 6V, 9V or 12V),
> >with not too loud a click?
> You cannot use a relay with the above specs.
> Consider this. Your thermostat turns your AC unit on and off. How does it
> that? There's no 10A 220V relay in the thermostat, right.
> The way that it works is that there's a 24VAC circuit that controls the
> contactors that are already in place. So instead of trying to insert yet
> another contactor into the loop, you simply control the 24VAC circuit.
> When I replaced my thermostat with a PIC based controller, I used 12V
> automotive relays to drive the 24VAC low voltage circuits. Since they
> were in the basement, I didn't worry too much about the click.
> Be aware that the you'll need to drive both the AC unit and the fan
> While the furnace will cut the fan on automatically, the AC unit won't.
> Please stay away from the high voltage, high current circuits. There are
> low voltage circuits that are a lot easier to manage. This is what John
> be not fooling with anything if you're asking these kinds of questions.