Air Conditioning/Thermostat Selection

[randallbrink]

..

Well, I've already installed a new thermostat, and still have the same symptoms. Odds are not good that two new thermostats would be faulty.

[randallbrink]

P.S. What should I expect to see happen with this procedure? And with what T'stat switch positions?

Thanks again!

[Telstra]

Cycling the system

Connecting R 24V Active from the transformer to the G Fan relay Y Compressor relay or W Heating relay will energise these relays regardless of the thermostat setting. If this does not occur then R is really Gand G R. That is the wire to G is really the 24V active and the wire to R is from the fan relay. However if it does work correctly then the thermostat wiring is correct and the fault is in the Indoor Unit either the transformer or the wiring. My guess is the wiring, perhaps a loose or burnt wire. The assumption of course is that the unit worked correctly when it was installed.

However it appears that the fault is in the indoor unit wiring

[randallbrink]

Thank you very much for this clarification. I will now carry out this test and see what happens.

[randallbrink]

OK--when R jumpered to G, A/C unit fan AND indoor central fan activates. As soon as jumper wire is removed, A/C unit fan stops. Indoor fan continues operating. (with t'stat switches in "auto" and "cool".

[Telstra]

To resolve the question as to the true 24V Active put the wire to the R terminal on G and the wire to the G terminal on R. and test the thermostat

OK--when R jumpered to G, A/C unit fan AND indoor central fan activates. As soon as jumper wire is removed, A/C unit fan stops. Indoor fan continues operating. (with t'stat switches in "auto" and "cool".

[M Q]

On many furnaces, the fan speed for A/C is different (and higher) than the fan speed for heating or for thermostat "Fan". The problem could well be in the furnace (where your fan is). It could be the higher speed winding on the motor is open, the connection to that winding is open, or there is a problem with the relay in the furnace that controls the fan. Contrary to the diagram on page 16 of the pdf for the outdoor unit, the "Y" wire often goes to the furnace and is used by the furnace to turn on the fan and select the speed.

[randallbrink]

Ah. Yes, this has a true ring to it, because that would explain why the fan works fine as long as "Cool" is not selected on the thermostat mode selector.

[randallbrink]

I just wanted to say "Thanks!" to everyone who helped during this situation. As it turns out, the central fan was incorrectly wired at the furnace circuit board, and once that was corrected, the air conditioning now works fine.

I appreciate all the advice.

[Mikepier]

.

So how was it incorrectly wired? Did someone else mess with the furnace?

[randallbrink]

...

It was incorrectly wired in that the fan speed switch was wired to high speed, but the central fan is only single speed. It appeared to have been wired that way when the unit was installed.