thermostat operation

[Ken Hilson]

Can someone save me some time with a ohmmeter and tell me what the
switching is in a standard heat/cool thermostat.
It has terminals RYWG. What is connected to what when set in 1. fan
(versus auto) irrespective of temp ie fan to run 2. heat required when set
to heat 3. cool required when set to cool
Thanks

 

[Nukie Poo]

Can someone save me some time with a ohmmeter and tell me what the
switching is in a standard heat/cool thermostat.
It has terminals RYWG. What is connected to what when set in 1. fan
(versus auto) irrespective of temp ie fan to run 2. heat required when set
to heat 3. cool required when set to cool
Thanks

R to G turns on blower
R to Y starts a/c compressor
R to W starts heat

 

[Romy Singh]

R to G turns on blower
R to Y starts a/c compressor
R to W starts heat

So when the A/C is running, would that mean R-G-Y are all connected
together?
(same for the heat, but with W)?


Thanks, (I've always wanted to know this)
Romy

 

[Nukie Poo]

So when the A/C is running, would that mean R-G-Y are all connected
together?
(same for the heat, but with W)?


Thanks, (I've always wanted to know this)
Romy

Correct

 

[daestrom]

So when the A/C is running, would that mean R-G-Y are all connected
together?
(same for the heat, but with W)?

Actually, for heat, you merely connect R and W. There is another
thermo-switch at the furnace (on the heat-exchanger) that will turn on the
blower *after* the burner has warmed up the heat-exchanger. This also keeps
the blower running for a few seconds after the burner shuts off.

IIRC, similar is true for cooling. When you connect R to Y, the A/C starts
and it starts the blower directly.

R to G is only connected when you turn the 'Auto-On' fan switch to 'On'.
The G is open-circuit any time the fan switch is in auto.

daestrom

 

[Ken Hilson]

Actually, for heat, you merely connect R and W. There is another
thermo-switch at the furnace (on the heat-exchanger) that will turn on the
blower *after* the burner has warmed up the heat-exchanger. This also keeps
the blower running for a few seconds after the burner shuts off.

IIRC, similar is true for cooling. When you connect R to Y, the A/C starts
and it starts the blower directly.

R to G is only connected when you turn the 'Auto-On' fan switch to 'On'.
The G is open-circuit any time the fan switch is in auto.

daestrom

Other research I did suggests what you say, almost. . In my case I have a
water pump activated with the R to W . It then activates the blower but it
appears that if I had manually set R to G I might change the speed of the
blower (can be wired for dfferent speeds, mine isn't but friend' is).
I read that some thermostats might activate both Heat and Blower for some
applications.
It said that for cooling the thermostat activated both the
compressor and blower. In my case based on wiring I see that as the only way
the blower
could be started for cooling. ie R to Y or compressor and R to G for blower
indicating
again that cooling would be different speed than heating if I had multiple
speeds wired.
Thanks

 

[Romy Singh]

Actually, for heat, you merely connect R and W. There is another
thermo-switch at the furnace (on the heat-exchanger) that will turn on the
blower *after* the burner has warmed up the heat-exchanger. This also keeps
the blower running for a few seconds after the burner shuts off.

IIRC, similar is true for cooling. When you connect R to Y, the A/C starts
and it starts the blower directly.

R to G is only connected when you turn the 'Auto-On' fan switch to 'On'.
The G is open-circuit any time the fan switch is in auto.

daestrom

Interesting. It would be easy to test this with a typical mechanical stat.
However, is it ok to use a DMM to test a digital setback stat (ie. any
current or polarity issues)?

Thanks,
Romy

 

[Dave M.]

Actually, for heat, you merely connect R and W. There is another
thermo-switch at the furnace (on the heat-exchanger) that will turn on the
blower *after* the burner has warmed up the heat-exchanger. This also keeps
the blower running for a few seconds after the burner shuts off.

On my newer furnace, programmable time delays are used for fan on and off

Dave M.