On Friday, November 29, 2019 at 11:27:29 AM UTC-5, wrote:
On Fri, 29 Nov 2019 07:01:57 -0800 (PST), trader_4
wrote:

On Thursday, November 28, 2019 at 9:41:03 PM UTC-5, wrote:
On Thu, 28 Nov 2019 17:11:06 -0800 (PST), trader_4
wrote:

On Thursday, November 28, 2019 at 12:28:16 PM UTC-5, Ralph Mowery wrote:
I have a Trane heatpump that is about 12 years old. In the summer it
cools fine.
Last winter the house was about 2 deg cooler than the thermostat was
set for. Noticed the inside air handler was running,but the outside
unit was not.

Checked and had power. The relay that puts power to the compressor and
fan was not pulled in. The coil did not have any voltage on it. The
circuit board has a led that blinks once per second like the paper in
the pump says it should if everything is ok.

I cut it off by the thermostat and then 5 minuits later turned it on.
Everything is working fine now. The heatpump did that to be about 3 or
4 times last year. I don't recall the temperature then,but today it was
about 40 deg F outside. It was 66 inside instead of 68 like it was set
for.

I don't mind calling a man for service, but there would not be anything
I know of for him to find. Any ideas on why the outside unit will not
cycle off and on like it should ?
Maybe it goes into the defrost mode and gets hung up ?

IDK how heat pump systems call for heat. Is there one wire that says
make heat, another one that turns the blower on? Or does one wire say
make heat and the system turns the blower on? If it's the latter,
then since the blower is running you can rule out the thermostat.
If it's two wires, then it's possible it's a thermostat problem.

I agree that calling for service on something like this is really bad.
They won't see it happening and even if they do, probably won't have
any more idea what to do that you do.

in the thermostat cable
The white wire calls for heat (W2 calls the toaster wire)
The green wire turns on the fan.
Yellow is AC
Going out to the condenser it is either an orange or blue wire that
turns on the reversing valve (manufacturer dependent)

But when it calls for heat does the thermostat activate the W wire and
the G fan wire? Or just the W wire? With furnaces, it only activates
the W wire, the furnace then turns on the blower. The G wire in the
furnace application is if you want to manually put the blower on,
without heat. That matters with Ralph's problem. If it takes two wires
to work it, then it's possibly a thermostat problem or issue with the W
wire. If it just takes activating the W wire, then the thermostat and
wiring aren't the problem, because his blower is running. I guess regardless
I would get it set up so that I could measure the voltage at the W and
G terminals at the air handler control board when it's having the problem.
That might require taping over a cut off switch on a panel.

I'd also inspect the relay on the control board that drives the compressor unit,
if possible. Maybe the relay is sticking/failing and sometimes it will not close to activate. He should also measure the voltage at the control board
that goes to the compressor when it's having the problem, see if it has
voltage or not. That would help determine if it's before that point or an
intermittent wiring problem going to the compressor unit. But it doesn't
seem like a wiring thing, since recycling the power restores normal operation.
So far, it sounds most likely a control board problem.

If it looks like that's it, he could buy a new one. If it turns out that it's
not that, very good chance he can sell it on Ebay and get most of his money
back. Very cheap compared to what it would cost to call out an HVAC guy.
the compressor.

The heat will not run unless the fan is on and depending on the
thermostat base, you might have to turn the fan switch on to get heat.
I am not sure about furnaces, I haven't seen one in 35 years but that
is how air handlers work.

Furnace is as I described. The thermostat just calls for heat on the W
wire (or wires if it's two stage), the furnace does the rest, ie turns
the blower on after the furnace has fired for a minute or so. Old
furnaces used to use a temp switch in the plenum to activate the blower.
New ones just use a time delay on the controller board.

An interesting side note with two stage furnaces. They can generally be
set up two ways. One is really the right and best way, which is to use
two heat call wires, one for each stage. The other way is to just use
one wire and set it up so the control board makes the call based on how
long the furnace runs. So, it starts at low stage, then if it's still
running after ~ 8 mins or so, it goes to high. Obviously that's far
from ideal. If you need a bigger increase in temp, you have to wait 8 mins
for it to kick up. And it also might kick up and then shut off in a just
another short period, if the temp was almost where it needed to be.

The thermostat knows what the req increase is and can invoke high stage
at the beginning. But it takes an extra wire, that many installs probably
don't have. It also takes a two stage thermostat.
I'd also bet that a lot of furnaces are installed using the inferior
method anyway, because the installers are half-assed, don't want
to change to a two stage thermostat, etc.




I do know you can run most heat only
furnaces on a 2 wire thermostat (just reading the instructions for
thermostats).

Bingo.



He is definitely in the situation where poking around
with a meter (even a 24v test light) and looking at the wiring diagram
is in order. Just throwing parts at it and trying to get lucky is
silly.

I agree, I'd do more investigating, starting with what the voltages are
at the inputs to the unit and at the activation terminal going to the
heat pump.