23 replies to this topic

[roomservicetaco]

I have a small home/office that is detached from my home and it has it's own A/C unit. Last Monday, I came into the office in the morning and the air handler was blowing air, but the A/C unit was not working, such that the A/C was blowing warm air.

Took the unit apart and got it to the point where the compressor was working but the fan was not spinning (I pressed the button labeled "High Pressure Control Release/Reset" though I'm not sure if pressing this button was what got the compressor turned on or not). Got the fan to spin manually, so figured the issue was just the capacitor.

Replaced the capacitor (original was 40/3 but the store had only 40/5, which they said would work) but now I can't get anything to turn on - either the compressor or the fan.

Is there a good way to troubleshoot what other parts may need to be replaced?

One other thing - when I first went to replace the capacitor, for some reason, there was still electricity going to the A/C even though I had turned off the breaker. I managed to get some sparks before I realized this and turned off the main feed to the house. Is it possible I shorted something or fried one of the electrical parts? Any good way to test what needs to be replaced?

Thanks.

Here are the relevant pictures (last one is of the unit with the replacement capacitor installed. It was smaller in diameter than the old one, so I needed to fill with some weather stripping.) The "reset" button is the red one at the bottom center of the first picture.

https://picasaweb.go...itionerAug2012#

[jumptrout]

Your picture link does not work for me.
You will need a volt meter to do the test.
Use the meter to verify 220volts at the incoming side of the contactor.
If voltage is good,press the center bar of the contactor by hand to see if the compressor and fan motor come on.
If they will come on,set the thermostat for COOL.
Then use the meter to check for 24 volts at the contactor solenoid terminals located on each side of the contactor.
If you have 24 volts here,replace the contactor.
If you do not have 24 volts here,re-set the pressure switch.
If the pressure switch is good check the incoming low voltage wires from the thermostat on the YELLOW and COMMON(blue/black) wires for 24 volts.
If no volts on YELLOW and COMMON either the thermostat is bad or you have a broken thermostat wire.

[RegUS_PatOff]

... Replaced the capacitor (original was 40/3 but the store had only 40/5, which they said would work)
... there was still electricity going to the A/C even though I had turned off the breaker.
... Is it possible I shorted something or fried one of the electrical parts?
... Any good way to test what needs to be replaced?
... https://picasaweb.go...itionerAug2012#

model number ?
1) 40/3 = 40 is for the Compressor ... 3 is for the Fan ... 5 is nearly 2x3 .. more important what voltage rating ?
2) something's wired wrong .. who knows ?
3) yes
4) .. won't know until the wiring is corrected
5) ... "Sorry, that page was not found."

[roomservicetaco]

Thanks. Let me see if this link works better for you: http://goo.gl/mUACR

RegUS - let me get some additional information for you as per your questions and get back to you.

[roomservicetaco]

Model number: UAPA-024JAZ - see picture here for entire label: https://picasaweb.go...080675971223330

Also, here are two pictures of the label on the new capacitor, as installed. I brought the old one to the appliance store, showed it to the guy, and he said this one would work:
http://goo.gl/LrIUz
http://goo.gl/C9GBU


Can you confirm that everything is ok and then I can follow jumptrout's suggestions for troubleshooting (or let me know if you have other suggestions).

Thanks.

[jb8103]

One other thing - when I first went to replace the capacitor, for some reason, there was still electricity going to the A/C even though I had turned off the breaker. I managed to get some sparks before I realized this and turned off the main feed to the house. Is it possible I shorted something or fried one of the electrical parts? Any good way to test what needs to be replaced?

It's possible the capacitor was still holding a charge. You should have not only a circuit breaker but also a service disconnect at the condenser. Hopefully this unit was professionally installed by a reputable contractor.

[jumptrout]

Voltage rating on the cap is good.
Trace your components for power both low and high voltage.
Look closely at the contact points on the contactor.
They may burned and deteriorated.

If everything works except the fan,replace the fan motor.
Get a motor rated for a 5 mfd cap.

Edited by jumptrout, 08 August 2012 - 05:58 AM.

[roomservicetaco]

It's possible the capacitor was still holding a charge. You should have not only a circuit breaker but also a service disconnect at the condenser. Hopefully this unit was professionally installed by a reputable contractor.

Thanks - capacitor still holding charge is possible. How do I locate/identify the service disonnect?

Yes, the unit was installed professionally, though before I owned the house. The capacitor replacement was the only thing I've done to it other than clean it.

[roomservicetaco]

Voltage rating on the cap is good.
Trace your components for power both low and high voltage.
Look closely at the contact points on the contactor.
They may burned and deteriorated.

If everything works except the fan,replace the fan motor.
Get a motor rated for a 5 mfd cap.

Thanks. Going to follow your prior instructions for testing voltage at contactor. Just to clarify - I can test the voltage at the screws on the top of the contactor, right? There is also a brown wire and a yellow wire running off the side of the contactor to the delay-on unit. Should I test those? What about the big black cylinder at the top with the red wires coming out?

[jumptrout]

Don't know what black cylinder/red wire you are referring to. Pictures are not coming up for me.

[Bullstok]

The cylinder you mention is a start capacitor with a relay to cut it off. Note that it is different than the run capacitor you have been dealing with. It is sort of the equivalent of a hard start capacitor nowadays. It boosts the compressor to get it going.

FYI: the dirt your ac is setting on was created slightly before the ac itself was created. Maybe within a week or so.

Edited by Bullstok, 08 August 2012 - 08:08 PM.

[roomservicetaco]

Thanks everyone.

Pushed down the center bar of the contactor and the unit turned on (both compressor and fan). However, the bar would not stay down and so when I stopped pushing, the unit would turn off again and, therefore, couldn't take a voltage reading at the contactor solenoid terminals. I presume that I need to change out the contactor...correct? Anything else I should change out while I'm doing that?

[jumptrout]

Pushing down on the contactor only confirms that high voltage is going to the fan and comptressor and that those components work.
Set the thermostat for COOL and lower the temperatture on the stat.
Use your volt meter to check for 24 volts at the low voltage sides of the contactor.
If you have voltage the contactor is bad.
If you do not have voltage it could be the thermostat,the low voltage wiring or a low pressure switch in the condenser circuit.
If you have a wiring diagram,post a picture of it here.

[jb8103]

I had a similar situation recently. Control voltage to the contactor is controlled by the anti-short cycle timer, in my case that was a small circuit board. It was not passing voltage to the contactor. We can rule out the capacitors since the compressor and condenser fan start when the contactor is manually actuated.

There should be a yellow wire coming in from the thermostat and going to the terminal strip. From there, either a yellow or a violet wire will continue to the anti-short cycle timer. Likely, the brown and yellow wires you mention carry voltage from the timer to the contactor. Check for 24 VAC across them when the thermostat is calling for cool.

But first, your service disconnect will be a gray metal junction box with a lid. It should be mounted right on the unit. It will have a thick gray cable leading into it (that's called the whip). Open that cover and you should see a pull-out connector or a heavy duty switch.

Edited by jb8103, 13 August 2012 - 08:40 PM.

[roomservicetaco]

Thanks for all the good information. A quick update:

1. Found the service disconnect - thanks, very helpful to use that.
2. Switched out the contactor
3. Unit still not working, but I realized that my multimeter is not working either so I can't accurately diagnose right now.
4. Here is a picture of the circuit diagram that's on the inside panel: https://picasaweb.go...003130614315954 It pretty unclear so I drew a diagram by tracing the wires to the different devices: https://picasaweb.go...086934698155634

Will pick up a new multimeter tomorrow. I think I understand where to take the 24v measurements, but, not sure how to pinpoint the thermostat,the low voltage wiring, the low pressure switch in the condenser circuit (what is that?), or the anti-short cycle timer.

Thanks.

[roomservicetaco]

Here is the drawing, in case it is not clear on picassa:

[jumptrout]

Remove the cover plate on the thermostat to view the wire connections.
Post the wire colors and their letter designation.
Example: Red on R....Yellow on Y....Blue on C.......etc.
The Time Delay Relay is most likely the problem since you replaced the contactor and got no joy.
Once you provide the thermostat schematic I can instruct you on by-passing the time delay.
Do you have a digital thermostat?

[roomservicetaco]

Yes, digital thermostat. Looks like White on W, Red on RC and another red connecting RH and RC, then Green on G, and Blue(?) on Y. Picture below.

The blower does come on when the thermostat is set to COOL, so at a minimum the thermostat is sending a signal out to that device.

Here is a pic of the thermostat:

Edited by roomservicetaco, 16 August 2012 - 07:36 PM.

[jb8103]

Blue on "Y" is the guy we're after. Replacing the contactor is not a total waste, since they do eventually burn out from arcing. A fresh one won't hurt a bit.

The anti-short cycle timer is the "delay on break" circuit you have marked there. Same thing.

The low pressure switch is probably inside the hermetically sealed compressor. Not to worry.

What you have marked "freon valve(?)" is intriguing.

But anyway, the thermostat cable is likely a brown jacketed cable coming from the house and leading into the lower section of the electrical box in the unit. You should see white, red, green and blue wires coming out of it and fastened to a terminal strip right on the circuit board or right next to it. (Blue should be yellow.)

The blue sends power to the contactor through the delay on break component. Jumptrout will explain how to bypass that, which is almost certainly the problem child here.

[jb8103]

Just FYI.The engineers prefer that we consumers do not stop and start the compressor more often than once every three minutes. This can happen when we fiddle with the thermostat, so a timer is built in to prevent a re-start.A digital thermostat also has a timer built in, which is why Jumptrout asked if you had a digital. Now he knows he can safely bypass the timer in the condensing unit, at least temporarily. Providing we see control voltage going in to the timer, but no control voltage at the contactor when the thermostat is calling for cool. Your problem should be solved after you follow his instructions.

Edited by jb8103, 17 August 2012 - 04:20 AM.