Y/cooling controls IBM on split systems?

[georgelass]

I don't believe I've ever (in my admittedly short career) ever
jumped out cooling on a split system--always used the tstat.

So it was a bit of a surprise to hear from two other techs
in the past two days that the wire to G/fan is not necessary
to start the indoor blower, that a call on Y/cooling automatically
starts the IBM. Assuming they are right, how long have units
done this? (I haven't had the opportunity in the past two days
to simply try it myself.)

Thanks.

[dandyme]

there is generally internal connection from y-g

g is for independent fan control (fan "ON")

hold on for this: if it's a mercury bulb t-stat; r-y @ ODU will bring ID blower on; not so much with digital t-stat

[rglasgow]

Systems with printed circuit boards generally turn on blower with a call for cooling. Can,t guarantee that they all do this. One thing that I have found on service calls is that some installers just connect G from stat and leave Y on board blank. This results in low blower speed because blower just thinks a call for continuos fan.

[skippedover]

Systems with printed circuit boards generally turn on blower with a call for cooling. Can,t guarantee that they all do this. One thing that I have found on service calls is that some installers just connect G from stat and leave Y on board blank. This results in low blower speed because blower just thinks a call for continuos fan.

This is only a half truth. In fact, a 1-stage system with a PSC motor could care less if there's anything attached to the 'Y' terminal at the air handler. Variable speed is another matter, since most systems have a constant airflow speed for the IBM that's considerably slower than that needed for full AC operation. In that case then, your statement is correct, the 'Y' terminal at the air handler low voltage block needs to see the signal for compressor operation so it will know how to operate the IBM and at what speed for how much time.

All of that having been said, most t-stats are where the signal originates for 'Y' and 'G'. But some systems, like some York systems I know, feed all the info to the outdoor unit and it decides from the outdoor board what's going to fire up indoors. Likewise with some of the new ECM motors the wiring is a little uncommon from days of old, whereby there is 120 or 240 volts constantly fed to the motor and sense signals are sent to the motor controller to differentiate between blower speeds and/or constant circulation. So...one must be fairly intimate with the equipment on which he/she is working to get it 100% correct.

[just_opinion]

This is only a half truth. In fact, a 1-stage system with a PSC motor could care less if there's anything attached to the 'Y' terminal at the air handler...

..

NOT TRUE


... Variable speed is another matter, since most systems have a constant airflow speed for the IBM that's considerably slower than that needed for full AC operation. In that case then, your statement is correct, the 'Y' terminal at the air handler low voltage block needs to see the signal for compressor operation so it will know how to operate the IBM and at what speed for how much time...



NOT TRUE ALSO.

Lennox CBX32MV (not the Icomfort model) A/H will run blower at Y speed regardless of having G signal or not. Same for Y2 and the same for W


Bottom line is "depend on the manufacture design"

[skippedover]

NOT TRUE



NOT TRUE ALSO.

Lennox CBX32MV (not the Icomfort model) A/H will run blower at Y speed regardless of having G signal or not. Same for Y2 and the same for W


Bottom line is "depend on the manufacture design"

Please read my statement that "MOST systems", which does not include ALL systems. I already acknowledged that some systems may operate differently. And even within a single manufacturer, you can find instances of different types of operation. So...MOST is not an all encompassing word.

[just_opinion]

This is only a half truth. In fact, a 1-stage system with a PSC motor could care less if there's anything attached to the 'Y' terminal at the air handler. ...

I am sorry. But could you please point to us where is the word "MOST" in this statement of yours.

[rglasgow]

You guys are getting all worked up about semantics. The original post stated that he had not seen this before now. Some PSC motors still need a "Y" signal because they have "G" set to low speed tap on calls from"G". And I will never ever say "always" because I have been in this field since 1983. I have seen things that I still don't understand.

[catmanacman]

i always land the wires on the circuit board the you don't have to worry about it