Air Conditioning condenser not working

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diggler306
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Air Conditioning condenser not working

Post by diggler306 » Mon May 07, 2018 10:43 pm

So I went to run my AC for the first time this year, and go figure, it doesn't work. I use the NEST thermostat (I have for years with no problem), and when I turned it to COOL, the furnace fan started up but it did not produce cold air. So I went outside to check the condenser, and it was not running.
I verified that the circuit breaker was on at the panel. I verified that the outside shutoff switch was on and that power was actually entering the condenser unit.

After some Googling, I'm starting to think maybe the capacitor is faulty, so I pull that out and use a multi-meter to test the capacitance. The capacitor is 40+5 MFD +/-5% 440VAC. My tests come out at 37.03 and 4.467. Technically both are over the 5% variance but would that be enough to cause the entire unit not to run? I also checked continuity and that seemed fine. I don't see any visual bulging which they say is a sign of a faulty one.

Is there something else I should be looking at?

Im in Saskatoon. Anyone know where I can buy a new capacitor? I think I'll just replace it and hope for the best. Cheaper than calling the repair man (which I may still have to do honestly lol)!


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Aaron
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Re: Air Conditioning condenser not working

Post by Aaron » Tue May 08, 2018 12:29 am

You know that the condenser is getting signal from the furnace to switch on, right? It's that two-wire signal cable... if you test 24 vac across the two wires outside, then you know that both the thermostat and furnace are calling for the condenser to be operating.

If you know you have 240V entering the condenser, then yes, there's some issue with the relay/solenoid switch or capacitors.

diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Tue May 08, 2018 12:41 am

What I do know is that after I killed the power to the AC unit, I checked for voltage using a non-contact tester on the signal cable coming from the furnace since the furnace power was still on. I had voltage there; I didn’t check for 24V specifically though.

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emtnut
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Re: Air Conditioning condenser not working

Post by emtnut » Tue May 08, 2018 4:54 am

diggler306 wrote:
Mon May 07, 2018 10:43 pm

I verified that the circuit breaker was on at the panel. I verified that the outside shutoff switch was on and that power was actually entering the condenser unit.
When you say power is entering the unit, is the contactor pulling in ?


And a side note *** It's early May, and you need AC in Saskatoon ??? :o :o :shock:
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diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Tue May 08, 2018 7:26 am

Hehe I know right? I think it peaked at 28C in the sun yesterday. The kids’ rooms were just too hot. The high is back down to 19 today and 13 tomorrow so we won’t need AC. :)

I didn’t put a meter on the other side of the contactor but I did a quick visual inspection and checked that all wires were making contact. Didn’t see any burning. The little magnet part moved freely. I get a little squirrely working with 240 so I try to touch as little as possible with the power on. Lol

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emtnut
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Re: Air Conditioning condenser not working

Post by emtnut » Tue May 08, 2018 7:55 am

If you're comfortable with the unit starting, with the cover off, and you beside it ...

If you watch the contactor, and have someone make the call for AC, you should physically see the contactor pull in.

If it doesn't, then it's either a bad contactor, or the furnace relay isn't sending 24Vac to it.
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diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Tue May 08, 2018 9:38 am

emtnut wrote:
Tue May 08, 2018 7:55 am
If you're comfortable with the unit starting, with the cover off, and you beside it ...

If you watch the contactor, and have someone make the call for AC, you should physically see the contactor pull in.

If it doesn't, then it's either a bad contactor, or the furnace relay isn't sending 24Vac to it.
That's a good test - I'll try that too, thanks!

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emtnut
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Re: Air Conditioning condenser not working

Post by emtnut » Tue May 08, 2018 9:57 am

diggler306 wrote:
Tue May 08, 2018 7:26 am
I didn’t put a meter on the other side of the contactor but I did a quick visual inspection and checked that all wires were making contact. Didn’t see any burning. The little magnet part moved freely.
I must have missed this part :?

If you pushed in the 'magnet' part of the contactor, the unit should fire up.
If the Caps were bad, you would just hear a 'Hummmmm'

You mentioned you verified AC power. Did you measure the 240V at the contactor ?
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Re: Air Conditioning condenser not working

Post by diggler306 » Thu May 10, 2018 10:54 am

Alright so I powered everything on and when I manually depressed the contactor, the unit fired up. So I made sure I had the Thermostat calling for cooling (the furnace fan does run when AC is on) then I put the meter on the 24V connections on the contactor and got nothing. Somewhere along the low voltage line I'm losing power.

What's the process for checking the low voltage circuit?

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emtnut
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Re: Air Conditioning condenser not working

Post by emtnut » Thu May 10, 2018 4:39 pm

Good ! Now you know your AC unit is fine.

If you follow the low voltage wires back to the furnace, you will find the AC fan relay. They usually use a separate transformer (one for the furnace, and one for the AC).

See if you have the 24Vac there, and check connections from the T-Stat.
If you don't find anything obvious, try to upload a pic.
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Aaron
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Re: Air Conditioning condenser not working

Post by Aaron » Thu May 10, 2018 9:32 pm

On my furnace the 24VAC line to the condenser outside, red and black, is tied directly to the same terminals as the yellow and blue wires coming from the stat. The black/blue is common and the red/yellow is the cooling signal.

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Re: Air Conditioning condenser not working

Post by diggler306 » Thu May 10, 2018 10:49 pm

Here's a few pics! One of my thermostat (yes I see teh red wire's jacket is cut), two of the condenser unit, and the last is the circuit board in my furnace.

One question I have:

- In the condenser photo, the red wire from the red/black thermostat wire is pigtailed to a blue wire that goes to a circular thing, then out to the contactor. What is that?
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Circuit board photo explanation:
- The red sleeved red/black wire is the wire going out to the condenser unit. Black to C terminal, Red to Y
- Nest thermostat wires: White (Heat) - W, Black (A/C) - Y, Red - R
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Attachments
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emtnut
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Re: Air Conditioning condenser not working

Post by emtnut » Fri May 11, 2018 6:21 am

On your furnace control board, you should read 24vac between C and R.
When the call for air is on, you should read 24vac between C and Y terminals.

You can also check at the AC unit outside, where the red and black are wirenutted to the blue yellow wires. It should read 24vac when the call for air is on.


If you're getting 24vac outside, then it is one of the pressure switches. Not likely the switch itself, but probably the unit is low on refrigerant.
If we get too that point, if you can get a good pic of the outside schematic, I 'May' be able to help a bit more. I'm not an HVAC guy, so if it's a refrigerant problem you may need to get someone out there.
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diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Fri May 11, 2018 7:54 pm

Update:

I checked R + C at the furnace control board and we had 28V. I checked C + Y with cooling call and had 27V.

So I checked the red/white thermostat wires in the condenser with cooling calling, and I only have 21V. See photo.

Is that voltage loss normal? The thermostat wire is likely only about 30ft. And I wonder if 21V is enough to engage the electromagnet on this contactor or not.

Also, there's still the issue that once I re-connect the red wire to the contactor, there's near 0V across teh contactor terminals. I ohm'd out the low voltage contacts and got 15 ohms. So let's assume that the contactor coil is good and 21V is enough to make; the black thermostat wire is wire nutted to a yellow wire that disappears into the condenser unit, then comes back out and connects to the other side of the contactor coil. Perhaps it's this side that is broken? Maybe a safety switch or something inside? preventing it from passing the voltage?
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diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Fri May 11, 2018 10:16 pm

Further to what I just said about losing voltage inside the unit... here is the wiring diagram for my Lennox 13ACX.

C and Y1 on the right side of the diagram show the thermostat wires. One goes directly to the contactor, the other routes through the pressure switches. Since I know I have 21V on teh thermostat wires but 0V at the contactor after routing through the switches, I'm going to guess that's likely my problem.
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Re: Air Conditioning condenser not working

Post by emtnut » Sat May 12, 2018 4:43 am

I'd say it's probably leaked some refrigerant and the low pressure switch is preventing it from turning on.

Your diagram shows an optional 'A4' timer. If equipped, this could be the problem. (timer stuck off or set to be off right now)
If you can access where the switches are, you could visually inspect the wires for corrosion.
You asked about the circular device as well. I can't quite make it out, but does the blue wire pass through it ? Not exactly wired like the Diagram, but I think it's a temp switch. You can check for resistance, or try to measure 24vac from the blue at the contactor to the black from the transformer to see if it's the problem.

I'm not up on all the R-410A rules, but you may be able to get a recharge kit for it. If not, you need someone with a refrigerant license out there.

*Edit* The low voltage is also odd. Since the wires aren't connected, there should be no voltage drop. In case you have a problem with the control wire, you can try to hook up the black and red directly to the contactor (you may need a short jumper for this). This will confirm if there is a problem with the control wire.
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diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Sat May 12, 2018 12:08 pm

emtnut wrote:
Sat May 12, 2018 4:43 am
I'd say it's probably leaked some refrigerant and the low pressure switch is preventing it from turning on.

Your diagram shows an optional 'A4' timer. If equipped, this could be the problem. (timer stuck off or set to be off right now)
If you can access where the switches are, you could visually inspect the wires for corrosion.
You asked about the circular device as well. I can't quite make it out, but does the blue wire pass through it ? Not exactly wired like the Diagram, but I think it's a temp switch. You can check for resistance, or try to measure 24vac from the blue at the contactor to the black from the transformer to see if it's the problem.

I'm not up on all the R-410A rules, but you may be able to get a recharge kit for it. If not, you need someone with a refrigerant license out there.

*Edit* The low voltage is also odd. Since the wires aren't connected, there should be no voltage drop. In case you have a problem with the control wire, you can try to hook up the black and red directly to the contactor (you may need a short jumper for this). This will confirm if there is a problem with the control wire.
RESOLVED!

I did a quick test and bypassed the pressure switches by running the black thermostat wire directly to the contactor - guess what? It engaged!

So I opened up the unit and cleaned the VERY DIRTY coils. Then found the pressure switch reset button (red button- see below) and pressed it - BOOM - fixed!

Not sure what tripped it - maybe the dirty coils? Starving for air? It may have tripped for a reason that could require a service call in the future, BUT for now it seems to be running fine.

I am SO happy that it's fixed, even if it WAS just a reset button. I learned a lot from looking into this problem - and I want to thank you guys for all your input and support! Forecast is calling for high 20's (Celsius) the next few days so just in time.

p.s. Interestingly, after I got it working, I tested the low voltage across teh contactor again and i was getting 26V which is higher than the previous 21V I saw straight off the thermostat wires. Strange.
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Re: Air Conditioning condenser not working

Post by emtnut » Sat May 12, 2018 7:52 pm

diggler306 wrote:
Sat May 12, 2018 12:08 pm

RESOLVED!

I did a quick test and bypassed the pressure switches by running the black thermostat wire directly to the contactor - guess what? It engaged!

So I opened up the unit and cleaned the VERY DIRTY coils. Then found the pressure switch reset button (red button- see below) and pressed it - BOOM - fixed!

Not sure what tripped it - maybe the dirty coils? Starving for air? It may have tripped for a reason that could require a service call in the future, BUT for now it seems to be running fine.

I am SO happy that it's fixed, even if it WAS just a reset button. I learned a lot from looking into this problem - and I want to thank you guys for all your input and support! Forecast is calling for high 20's (Celsius) the next few days so just in time.

p.s. Interestingly, after I got it working, I tested the low voltage across teh contactor again and i was getting 26V which is higher than the previous 21V I saw straight off the thermostat wires. Strange.
Glad to see you got it going :)

Now you're all set for the 2 weeks of summer you get in Saskatchewan :mrgreen:
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diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Sat May 12, 2018 7:55 pm

emtnut wrote:
Sat May 12, 2018 7:52 pm
diggler306 wrote:
Sat May 12, 2018 12:08 pm

RESOLVED!

I did a quick test and bypassed the pressure switches by running the black thermostat wire directly to the contactor - guess what? It engaged!

So I opened up the unit and cleaned the VERY DIRTY coils. Then found the pressure switch reset button (red button- see below) and pressed it - BOOM - fixed!

Not sure what tripped it - maybe the dirty coils? Starving for air? It may have tripped for a reason that could require a service call in the future, BUT for now it seems to be running fine.

I am SO happy that it's fixed, even if it WAS just a reset button. I learned a lot from looking into this problem - and I want to thank you guys for all your input and support! Forecast is calling for high 20's (Celsius) the next few days so just in time.

p.s. Interestingly, after I got it working, I tested the low voltage across teh contactor again and i was getting 26V which is higher than the previous 21V I saw straight off the thermostat wires. Strange.
Glad to see you got it going :)

Now you're all set for the 2 weeks of summer you get in Saskatchewan :mrgreen:
Haha she’s fast and furious for sure! Thanks!

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emtnut
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Re: Air Conditioning condenser not working

Post by emtnut » Sat May 12, 2018 8:04 pm

Finally has been nice here in Ontario, for a few days ... If this keeps up, we may get 2 1/2 weeks of summer :mrgreen:

Thanks for getting back... I wasn't aware of the reset on those pressure switches. I'll keep it in mind if someone else has a similar problem.

Cheers,

Nutz
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Aaron
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Re: Air Conditioning condenser not working

Post by Aaron » Sun May 13, 2018 2:56 pm

I think I heard reports of frost in northern Minn, so I think our summer has wrapped up for the year now. lol

diggler306
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Re: Air Conditioning condenser not working

Post by diggler306 » Mon May 14, 2018 9:53 am

Aaron wrote:
Sun May 13, 2018 2:56 pm
I think I heard reports of frost in northern Minn, so I think our summer has wrapped up for the year now. lol
emtnut wrote:
Sat May 12, 2018 8:04 pm
Finally has been nice here in Ontario, for a few days ... If this keeps up, we may get 2 1/2 weeks of summer :mrgreen:
The "joys" of being Northerners eh? :D

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