My home A/C was turned on yesterday, and we realized that it blows
warm air instead of cold. I did a little bit of investigation and also
changed the filter.
* The outside unit fan is running, but the compressor itself
seems to be not running. I measured amps going to it, it is about
1.4 amps 220v, consistent with only the fan running.
* The cold refrigerant line (with thermal insulation) is not actually
cold but warm.
* I just changed a filter. The evaporator coil was not easy to see so
I did not look at it.
Would you have any troubleshooting suggestions. The outside unit is
relatively new. Thanks
The first thing you check is to be sure there's 220v to the relay . Then
that the relay closes when you call for cooling - and that 220 is getting
out of the motor side of the contactor . Next is the start cap , if the top
is bulged it's for sure dead . If not , I'm sure you have a meter that
measures capacitance . You might want to disconnect the fan power
temporarily to see if the compressor hums when first energized then quits
trying . No hum probably means it's dead or not getting power for some
reason , hum then click and stop indicates a high probability it's the cap .
If the compressor runs but no cooling , check the lines <where you can see
them> for an oil stain , which indicates a leak at that spot .
Do be sure to shut off power to the unit while you've got your fingers in
there unless you're actually checking voltage or performing tests . But you
knew that .
Guys, thanks a lot for your help.
I have a business buying and selling industrial parts and doing some
industrial scrap metal. So I think that I can troubleshoot this. I do
not have any experience working with refrigerant.
My understanding is, the compressor has a single phase motor with
external capacitor and resettable overload relay, right?
So, I would check, first, if there is 220v coming in (there likely is
since the fan runs), secondly whether there is 24v coming into the
coil of the contactor. If yes, I would check the overload relay. Maybe
after this, turn off the system for 30 minutes and turn it back on to
see if there is any humming or running compressor motor.
Then I should have a good idea if the problem is in the boards, power
coming in, relays, or capacitor, right?
On Sunday, May 3, 2015 at 10:01:47 PM UTC-4, Ignoramus18130 wrote:
If there wasn't 24V going to the contactor, the fan wouldn't be
running. That would seem to suggest that the contactor/relay is
OK too and supplying 240V to the output side which goes to the
fan and compressor.
On Sun, 03 May 2015 17:07:02 -0500, Ignoramus18130
Leave the system off a while so the thermal has time to reset if it
tripped. Turn it on while someone is out by the condenser and listen
for a loud hum that stops in 15-20 seconds.. If you are getting that,
then try the start cap.
Bear in mind these things usually have a time delay on the compressor
and if the power was off, it may not start right away although the fan
will be running. Give it 5 minutes or so before you give up.
The transistorised timer in my ancient Carrier A/C was intermittant. It
would sometimes not turn on and sometimes turn off for no reason
If it turned off then later came on again another 3 minutes elapsed
befor the compressor came on.
Having a long expierince in electronic problem solveing I had 2 A/C
techs look at it before I decided to observe very carefully myself.
Some judicious banging on the case and watching revealed the above.
New timer works like a dream. :-)
1) Where are you located? The reason that I ask is that I am located in an
area where my gas and electric utility provider has a deal where they will
come out and look at a broken item such as HVAC, figure out what is wrong,
and give a price to fix it. If I don't use them to fix it, there is no
charge for the visit. So, it's a free diagnosis. If you are lucky enough
to have a utility company that provides that free service, let them check it
out for you. I sometimes pay them to do the work if it is something basic
and not too expensive. Their repair prices are high in general, but
sometimes they can just fix what's wrong while they are there and I'm done
2) Since the condenser fan is running, this may not be applicable, but two
times recently when my AC was just blowing hot air it was because the lawn
company accidentally weed-whacked the 24-volt wire running to the condenser
(two different properties).
OK, guys, thanks to those who encouraged me to look further.
Again, what was happening before was that the fan was running, but the
compressor was not running.
I turned off the thermostat altogether, for several days, due to cool
weather. Today, the weather was warm enough to try looking into my AC
I turned the thermostat to COOL and nothing at all is happening. The
furnace fan is not blowing and the outside compressor and fan are not
running at all.
This is a change from 4 days ago, when at least something was running,
now nothing is running.
I spent some time today investigating this. This is what I found:
*) There is 120 volts coming into the furnace from the circuit breaker
*) There is 120 volts on the input of the 24 VAC transformer
*) There is no 24 VAC on the output of the transformer, the output is
0 volts AC.
*) The secondary (low voltage) winding has resistance appx. 1 ohm
*) The primary (high voltage) winding has infinite resistance, in
other words it is broken.
So, on its face the answer is that my air conditioner is not working
because the control transformer is not functioning. It should be easy
What I am not sure is why it failed. Did it happen simply due to age,
or there was perhaps overdraw of current or a short in the 24v system
that caused it to fail? Any thoughts on this?
I can easily find a 120->24v transformer, but I am not sure if I found
the root cause or not.
OK, I think that I understand what happened, the root cause.
The cause was that the contactor for the outside compressor was not
closing properly. That is why the compressor was not running
Because the contactor would not close, the contactor coil used
excessive current. After a while of this, the control transformer
I actually figured this out just by sitting and thinking.
Then I went outside, opened the control area of the compressor unit,
and found the following confirming evidence:
1) The compressor motor works just fine when I push the contactor to
close, by hand
2) The contactor coil stinks and looks blackened/browned, instead of
wholesome gold like color.
3) The coil also stinks, like burned out coils are wont to do.
So, I think, that I am looking at replacing both the contactor unit,
as well as the transformer.
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