Hi meirman, hope you are having a nice day

On 02-Aug-03 At About 04:51:53, meirman wrote to All
Subject: Thermostat Wiring

m From: meirman


m I think the terminology here might be a problem. On the thermostats
m I've used, if you turn the fan switch to ON**, the fan runs whether
m the A/C is on or not.


Think of it as a double pole single throw relay. G is common and there is R
and Y, when you are in auto G is connected to Y internally so that when Y (
cooling ) calls the fan runs at the same time. when you switch it to Fan On
it connects to R and disconnects from Y

m The A/C might be enabled***, but unless the
m house is hot enough that the the temperature setting is lower than
m the house temperature at the thermostat, and the compressor is
m running, I don't think most of us would say that the A/C has "come
m on".

See above.


m ***I"m not sure the industry term for this, but I mean by "enabled"
m that the A/C is ready to run as soon as the house is hot enough to
m cause the thermal switch to turn it on. What is the industry term
m for this? **Peter is trying to duplicate the ON setting for the fan
m switch, not the AUTO setting.

See above.

m To us, it's hard to understand when you say it runs the fan when the
m A/C comes on, if it runs the fan all the time.

See above.


m If there is an internal connection from the G to the Y, which is the
m primary cool call relay, what would happen if that internal
m connection was broken and the thermal part of the thermostat was
m relied on to turn on the compressor?

There is no "thermal part" to turn on the fan. again, see above.


m if you parallel that, whenever you run the new switch you will run
m the A/C and damage it.

m Do you mean, because even though the fan and compressor are on,
m eventually the house will be as cold as the A/C can make it, but it
m will keep running? Would that damage it?

Yes it will damage it. anything below abut 68 degrees indoor can cause the
evaporator to freeze which will slug the compressor with liquid refrigerant
and damage it.

m If you mean that would damage it, what happens if I use my current
m thermostat and set my A/C on and my thermostat to 33 degrees, and my
m fan on AUTO or ON?

early death for the compressor.

m Even without modifying the thermostat, how come we don't damage our
m A/C's when we have the A/C-Heat switch set to OFF and the Fan switch
m set to AUTO or ON?

see above.

m Can we damage our A/C just by setting the thermostat to settings we
m don't always use?

I don't know what you mean here but running the A/C anywhere below a 68
degree setpoint will cause excessive wear and early compressor failure.



-= HvacTech2 =-


... "Are there any questions?" - s.w.

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