Central Air conditioner troublshooting

[smc]

Central Air conditioner troublshooting

Moved into a 2011 home in December, just now testing out the central air conditioner.

It will not turn on, neither the fan or the compressor. The setting the thermostat to cool does activate the switch on the a/c unit. I have taken the panel off to verify. The a/c is getting 120V from two wires so I guess 240 total (or maybe I am measuring the voltage in the wrong spot). There is a very faint hum regardless if the unit is fuse for the a/c is on or off.

Thoughts? The unit is less than three years old. The capacitor looks fine.

Thanks

[Darell_n]

Your furnace will energize the contactor in the outdoor condensing unit, even with the 240v disconnected. (this is the humming sound when calling for cooling). I would check for voltage drop across the contact with it pulled in (should be 0 volts per phase) After that I would need a schematic to see the safeties in the circuit. You may be simply out of gas.

[jeffh]

I had a similar problem recently that was the result of a faulty relay on my board. Difference is my fan on my outdoor unit would turn on, but nothing else. So, based on that, I think your problem rests with something earlier on in the sequence. I'd check your tstat(thermostat) and its wires/connections, make sure none of the wires have loosened. I am pretty sure there is a way to jumper your tstat controls at the board's 'tstat connectors' to rule out a faulty tstat.

[smc]

Originally posted by jeffh
I had a similar problem recently that was the result of a faulty relay on my board. Difference is my fan on my outdoor unit would turn on, but nothing else. So, based on that, I think your problem rests with something earlier on in the sequence. I'd check your tstat(thermostat) and its wires/connections, make sure none of the wires have loosened. I am pretty sure there is a way to jumper your tstat controls at the board's 'tstat connectors' to rule out a faulty tstat.

It definitely isn't an issue with the thermostat. When I sent the thermostat to cool, the contactor closes. I'll check the voltage across the contractor tonight to make sure it isn't broken.

[Darell_n]

Post a pic of the wiring diagram in the outdoor unit.

[Maxt]

Does it have an outdoor disconnect switch and is it on?

[smc]

I'll post a pic tomorrow.

It does have an outside disconnect and it is on. I have measured the power going to the a/c unit with a voltmeter.

[smc]

Not sure if these are useful but I'll post anyway

http://www.n-images.net/Beyond/ac1.jpg
http://www.n-images.net/Beyond/ac2.jpg
http://www.n-images.net/Beyond/ac3.jpg
http://www.n-images.net/Beyond/ac4.jpg
http://www.n-images.net/Beyond/ac5.jpg
http://www.n-images.net/Beyond/ac6.jpg
http://www.n-images.net/Beyond/ac7.jpg
http://www.n-images.net/Beyond/ac8.jpg
http://www.n-images.net/Beyond/ac9.jpg
http://www.n-images.net/Beyond/ac10.jpg

[rage2]

So my A/C has been inconsistent every spring. The only pattern I can find is that the outside air isn't hot, basically ~15C and under.

Is there a outside temp sensor that disables the A/C at a set temp to reduce the chance of the coils freezing? Or are my coils actually freezing?

[Darell_n]

Originally posted by rage2
So my A/C has been inconsistent every spring. The only pattern I can find is that the outside air isn't hot, basically ~15C and under.

Is there a outside temp sensor that disables the A/C at a set temp to reduce the chance of the coils freezing? Or are my coils actually freezing?

The low ambient control will prevent the compressor from starting and damaging itself when it's too cold outside. These are optional on residential units and are typically at 55*F (12.7*C) for commercial units without crankcase heaters. The indoor evaporator coil may also have a freeze stat to prevent ice formation. Low air flow (dirty filter or coil) or low refrigerant charge are the common causes.

[Maxt]

Put voltmeter on yellow and black at the top of the contactor (21)-(28) should be 220-240 volts ac
Blue and brown are the control wires should be in the range of 24 volts when thermostat is asking for cooling.
Red and black at bottom should have 220-240 ac when contactor is energized( blue and brown have 24 ac.

[Darell_n]

SMC, your photo has the contactor not pulled in and is the de-energized state. There should be no humming or call for cooling. If you force on the A/C the contactor should pull in and you should measure 24Vac on the small blue and brown wires.

A quick test you can try with the outdoor unit powered up is to quickly press in the contactor with a plastic pen. The compressor and condenser fan motor should run as long as the contactor is held in. If they both run, then you have a control problem.

[Maxt]

I should ask if anyone has been into the main panel at some time? Its possible to stab the 2 pole breaker into the same bus so you end up with the same phase of 120 on both poles of the breaker instead of 240 from different phases.

[smc]

Originally posted by Darell_n
SMC, your photo has the contactor not pulled in and is the de-energized state. There should be no humming or call for cooling. If you force on the A/C the contactor should pull in and you should measure 24Vac on the small blue and brown wires.

A quick test you can try with the outdoor unit powered up is to quickly press in the contactor with a plastic pen. The compressor and condenser fan motor should run as long as the contactor is held in. If they both run, then you have a control problem.

When the photo was taken the A/C signal from the thermostat was off. There was no humming. When the thermostat is set to cool the contactor does pull in, but nothing runs :(

If I push hard on the contractor pin I get a louder sound, but still nothing starts.

[smc]

Originally posted by Maxt
I should ask if anyone has been into the main panel at some time? Its possible to stab the 2 pole breaker into the same bus so you end up with the same phase of 120 on both poles of the breaker instead of 240 from different phases.

Thanks Maxt!!!!

The bus was the problem. It is now working. It was drawing only 120V before.

[Crazyjoker77]

Originally posted by smc


Thanks Maxt!!!!

The bus was the problem. It is now working. It was drawing only 120V before.

its actually very easy. put your voltmeter on terminals 11 and 23 you should see ~240v means everything is fine breaker side.

If it reads 0v between 11 and 23 then use your meter and measure each one individually to ground (that lug with the green wire) if both have 120V to ground and nothing between the two terminals the breaker is incorrectly installed in the panel.

[rage2]

Originally posted by Darell_n
The low ambient control will prevent the compressor from starting and damaging itself when it's too cold outside. These are optional on residential units and are typically at 55*F (12.7*C) for commercial units without crankcase heaters.
Thanks man, means I'm not going crazy haha. Yesterday was one of those days where it wasn't hot out, but the sun was global warming my whole house. A/C wasn't going and house hit 27C. Brutal.

[benyl]

Originally posted by rage2

Thanks man, means I'm not going crazy haha. Yesterday was one of those days where it wasn't hot out, but the sun was global warming my whole house. A/C wasn't going and house hit 27C. Brutal.

Open the windows?

I have 12 SW facing windows and the sun will heat our house to 30C when it is -10 outside. My A/C still has the cover on it. We just open the window. haha (yes, I am cheap).

[Jeff TYPE R]

Originally posted by rage2
the sun was global warming my whole house.

http://www.iflscience.com/sites/www.iflscience.com/files/styles/ifls_large/public/blog/%5Bnid%5D/billboard_0.jpg

[hedge]

For some reason mine is termpermental the first time in the season. The house fan will come on but the outside unit will not. I'll try it again later and it will then start up. Only seems to be the first time in the season and then it's fine the rest of the summer.

I've had 3 different companies in to check it and they can't find anything wrong and of course it works fine when they are there. Frustrating.

[rage2]

Originally posted by hedge
For some reason mine is termpermental the first time in the season. The house fan will come on but the outside unit will not. I'll try it again later and it will then start up. Only seems to be the first time in the season and then it's fine the rest of the summer.

I've had 3 different companies in to check it and they can't find anything wrong and of course it works fine when they are there. Frustrating.
I'll bet it's the same issue I had haha. I've done the exact same thing for a few years, call for service, nothing is wrong, works when they show up. Apparently they don't turn on when it's too cold outside.

[ExtraSlow]

Retro-bump, but it fits the topic and I don't think it makes sense to start a new thread.

I have a problem with my air conditioner freezing up. Usually just means I need to change my furnace filter, but it froze overnight last night, even though I had replaced the air filter yesterday. Could see visible frost on it outside, and inside, once I shut it off, water was pouring out of the drain pipe from the furnace.

During cooling season, I replace the furnace filters about once per month, and I use the cheapo ones to allow more airflow.

House is two-story, and dark stucco, so it really soaks up the heat in the afternoon and evenings. I've needed AC on days it was 10 degrees outside! Stupid attached infills, it's very hard to get a cross breeze going with the windows, and obviously, when it's 28 degrees like yesterday, we don't even try. On warm days, the AC unit runs pretty much constantly from around 4 PM until midnight.

So some questions:
1) does freezing up damage the unit? am I going to wreck something?
2) is there maintenance I should be doing aside from replacing the furnace filter?
3) I have it set to allow the house to warm up slightly during the day, to a max of 21.5, and then cool it down all evening, in increments, to 19 degrees overnight. Am I asking too much with that temp swing?
4) we have a few vents closed on the main floor so we don't freeze while watching TV. I've always assumed that there would be sufficient airflow elsewhere that it wouldn't matter. Now I'm not sure. Am I choking the flow too bad and causing freezing?
5) is there a thermostat that will cycle the AC unit and allow it to dry off / defrost one an hour or something? Seems like it would be easy to get rid of small amounts of moisture that way.

Thoughts or suggestions guys?

[Darell_n]

You might be low on refrigerant. The evap coil in your furnace is designed to run at 4°C and will get colder and start to freeze if the refrigerant level causes the compressor suction pressure to drop too low. Insufficient airflow is the other freeze up cause, as you have already mentioned.
I've only seen building water damage from a/c freezeups but ice crush damage is common in commercial freezers and coolers. As for a defrost timer, 99% of all coolers and freezers use them, including your fridge at home and a cheap Grosslin timer can be installed easily in your outdoor unit. This is certainly not the proper way to fix it and is just a bandaid.

[BokCh0y]

Hopefully this is the right place rather than starting a new thread, so just gonna treat this as a general AC help thread.

Just got AC installed last week via Action Furnace. AC works great, but I can't seem to get it to really cool the upstairs down. Upstairs is always 3-4 degrees celcius warmer. How can I increase air flow upstairs? i saw at home depot they have these fans you can install in the ducts that are supposed to run off the furnace. Would these help?

i've already gone and closed all the vents in the basement and the main floor and this has helped a little but not as much as i'd like. The upstairs vents are just so weak. This is an issue too in winter but maybe not as bad.

Thanks.

[RealJimmyJames]

Would running bathroom fans on the top floor help suck some warm air out?

[jeffh]

Install volume dampers after the take offs on all the pipe run-outs in your basement supply duct line. Closing the dampers close to the main trunk line should significantly help.

I think am going to eventually run a new 9" pipe up to my 2nd floor hallway, through a closet and right close to my main plenum. That'll be done sometime after i hook up ac.

[bigboom]

Kind of related question but does blocking off the cold air returns upstairs help keep the upstairs cold and basement from freezing?

[jeffh]

I think you'll have the opposite effect, alternatively you can try blocking the main floor returns somewhat, play around with it. Just dont overdo it as it could put strain on your blower.

[jeffh]

I run my upstairs bathroom fans in the evenings, it seems like it keeps the house a bit cooler. They are fairly cheap to run as well. But i dont think running those fans when you have central ac is the solution you'd be looking for.

[Maxx Mazda]

Any tips to make my central AC more efficient? (house built in 2005)

Main floor (where the thermostat is) gets nice and ice cold while the upstairs is still hot. I also have a "ventilation fan" should I be running this in the summer or not? Seems to be connected to cold air return and runs directly outside.

[benyl]

Originally posted by ExtraSlow
Retro-bump, but it fits the topic and I don't think it makes sense to start a new thread.

I have a problem with my air conditioner freezing up. Usually just means I need to change my furnace filter, but it froze overnight last night, even though I had replaced the air filter yesterday. Could see visible frost on it outside, and inside, once I shut it off, water was pouring out of the drain pipe from the furnace.

During cooling season, I replace the furnace filters about once per month, and I use the cheapo ones to allow more airflow.

House is two-story, and dark stucco, so it really soaks up the heat in the afternoon and evenings. I've needed AC on days it was 10 degrees outside! Stupid attached infills, it's very hard to get a cross breeze going with the windows, and obviously, when it's 28 degrees like yesterday, we don't even try. On warm days, the AC unit runs pretty much constantly from around 4 PM until midnight.


A couple of things. My understanding is that freezing happens when the unit is undersized. So it runs constantly.

Also, your furnace / thermostat should be reading the flow and shutting down when the flow is restricted by ice. Unless you have a really old ass furnace.

[nzwasp]

What is the role of a cold air return when air conditioning is in use?

[Masked Bandit]

Originally posted by ExtraSlow
Retro-bump, but it fits the topic and I don't think it makes sense to start a new thread.

I have a problem with my air conditioner freezing up. Usually just means I need to change my furnace filter, but it froze overnight last night, even though I had replaced the air filter yesterday. Could see visible frost on it outside, and inside, once I shut it off, water was pouring out of the drain pipe from the furnace.

During cooling season, I replace the furnace filters about once per month, and I use the cheapo ones to allow more airflow.

House is two-story, and dark stucco, so it really soaks up the heat in the afternoon and evenings. I've needed AC on days it was 10 degrees outside! Stupid attached infills, it's very hard to get a cross breeze going with the windows, and obviously, when it's 28 degrees like yesterday, we don't even try. On warm days, the AC unit runs pretty much constantly from around 4 PM until midnight.

So some questions:
1) does freezing up damage the unit? am I going to wreck something?
2) is there maintenance I should be doing aside from replacing the furnace filter?
3) I have it set to allow the house to warm up slightly during the day, to a max of 21.5, and then cool it down all evening, in increments, to 19 degrees overnight. Am I asking too much with that temp swing?
4) we have a few vents closed on the main floor so we don't freeze while watching TV. I've always assumed that there would be sufficient airflow elsewhere that it wouldn't matter. Now I'm not sure. Am I choking the flow too bad and causing freezing?
5) is there a thermostat that will cycle the AC unit and allow it to dry off / defrost one an hour or something? Seems like it would be easy to get rid of small amounts of moisture that way.

Thoughts or suggestions guys?

I've run into the problem of the unit freezing up as well and aside from being diligent on changing your filters, which it sounds like you're doing, I found that running the furnace fan constantly eliminates the issue. The side benefit is that if you're always moving that air around in the house you balance out the temperatures both upstairs & down. On really warm days like yesterday & today if I let the house get up to 21.5 / 22 the AC can't catch up until a few hours after the sun goes down. On a day where the temperature hits the high 20s the upstairs will hit 24-25 by 7:00 PM if I don't keep it at 20 through the day.

[Crazyjoker77]

Originally posted by nzwasp
What is the role of a cold air return when air conditioning is in use?

Its just like the recirc button in your car. Its better to pull ~23c air from inside the house and cool it than it is to pull ~28c+ from outside and have to cool that.

A dirty A coil (evaporator) can also increase your risk of freezing. They are usually a pretty big PITA to clean but is something that should be done. High humitidy will also increase the chance of it freezing up.

Running an exhaust fan or "ventilation fan" only works when the outside is cooler than inside. It exhausts the air in the house which creates a low pressure within and will replace that with air from outside.

[BokCh0y]

Still no answer on this...sounds like Maxx Mazda is having a similar issue as I am. How can we make the unit more efficient in that the upstairs is cooled properly?

If i bought those ventilation fans that you can install in the venting, would that help the airflow? What i'm seeing right now is the upstairs just isn't blowing hard enough to cool the room and push the hot air into the cold air return back to the furnace.

Something like this help:

https://www.homedepot.ca/en/home/p.square-of-round-ducts-air-booster.1000509032.html

https://www.homedepot.ca/en/home/p.4-inch-with-pressure-switch.1000745620.html

https://www.homedepot.ca/en/home/p.duct-under-mount-air-boostercfm.1000509033.html

[kenny]

Originally posted by Maxx Mazda
Any tips to make my central AC more efficient? (house built in 2005)

Main floor (where the thermostat is) gets nice and ice cold while the upstairs is still hot. I also have a "ventilation fan" should I be running this in the summer or not? Seems to be connected to cold air return and runs directly outside.

If you have a single furnace in the house and only your main floor is cool, close up the air returns where it is cold and keep the fan running 24/7.

[nzwasp]

I have this issue too but ive just come to accept that while the ground floor is 20 degrees the upstairs will be 22 and im ok with that.

Those damper fans that you get at homedepot though, my neighbor got pete the plumber to install them in his ducts to the tune of $3000 which I think is insane, surely it doesnt cost that much.

[jeffh]

Nzswap, the purpose of your cold-air return is to circulate the air. Try not to think of it as a 'cold-air' return, but simply 'return-air'. When you bring in newly conditioned air(hot/cold/humid/dry/filtered/etc) through your 'supply' grilles, there needs to be somewhere for the stale air to go. For the most part, that stale air will flow through your return air grille. It is essential that there is an open return near an open supply for your system to operate properly.

Sidenote, having to install aduct inline booster fans in individual supply air lines is a sign of poor initial design and/or install. Personally, I'd look at upsizing(eg. 5"--->6"pipe) branch lines, and streamlining the elbows as much as possible(eg. Eliminating regular 90s, in favour of 30/45deg bends or full radius 90s).

[Darell_n]

Most 2 story houses have crappy hvac design due to cheap builders and cheap design and owners not knowing better.

[jeffh]

^ absolutely correct

[ExtraSlow]

Originally posted by benyl


A couple of things. My understanding is that freezing happens when the unit is undersized. So it runs constantly.

Also, your furnace / thermostat should be reading the flow and shutting down when the flow is restricted by ice. Unless you have a really old ass furnace. My unit may be undersized, or I may have just been asking it to drop the house temp too much. It can hold the temp stable regardless of weather without running constantly.

I don't think my thermostat has any function to read "flow". When it ices up, if I don't notice, it just keeps churning away all night. Wouldn't call it old ass either, furnace is from 2008 maybe? Thermostat is a couple years newer, decent honeywell wireless unit.

[bigboom]

Originally posted by ExtraSlow
My unit may be undersized, or I may have just been asking it to drop the house temp too much. It can hold the temp stable regardless of weather without running constantly.

I don't think my thermostat has any function to read "flow". When it ices up, if I don't notice, it just keeps churning away all night. Wouldn't call it old ass either, furnace is from 2008 maybe? Thermostat is a couple years newer, decent honeywell wireless unit.

Also, from what I was told make sure you aren't using a really good filter either as reduced air flow can also cause the evap coils to freeze up.

[benyl]

Originally posted by ExtraSlow
My unit may be undersized, or I may have just been asking it to drop the house temp too much. It can hold the temp stable regardless of weather without running constantly.

I don't think my thermostat has any function to read "flow". When it ices up, if I don't notice, it just keeps churning away all night. Wouldn't call it old ass either, furnace is from 2008 maybe? Thermostat is a couple years newer, decent honeywell wireless unit.

Some furnace / thermostat combinations talk to each other.

For instance, my thermostat will tell me when to replace my filter basic on the static flow that is read by the furnace.

Do you run the fan when it isn't cooling?

[BokCh0y]

Originally posted by jeffh
Nzswap, the purpose of your cold-air return is to circulate the air. Try not to think of it as a 'cold-air' return, but simply 'return-air'. When you bring in newly conditioned air(hot/cold/humid/dry/filtered/etc) through your 'supply' grilles, there needs to be somewhere for the stale air to go. For the most part, that stale air will flow through your return air grille. It is essential that there is an open return near an open supply for your system to operate properly.

Sidenote, having to install aduct inline booster fans in individual supply air lines is a sign of poor initial design and/or install. Personally, I'd look at upsizing(eg. 5"--->6"pipe) branch lines, and streamlining the elbows as much as possible(eg. Eliminating regular 90s, in favour of 30/45deg bends or full radius 90s).

Thanks for this.

Would it even make a difference once the vent starts to go upstairs? Clearly anything upstairs of the basement is finished and sealed, so increasing the ducting from say 5" to 6", the bottle neck would still be when the duct goes upstairs behind the walls and such correct? So what would be the point?

[jeffh]

It would make a difference on longer lines and ones with multiple bends. it would help to supplement the friction loss in those runs. I deal with this exact issue all the time in the commercial industry. You are correct in saying it'd bottleneck, but at least you are getting as much air volume as you can just before the line heads upstairs. Think about if you have a 50' long line compared to a 25' long line, you must expect the volume of air exiting the 25' line would be noticably greater than the 50' line.

Increasing pipe sizes where necessary is way cheaper and simpler than installing booster fans in similar spaces.

Glad I can help.

[BokCh0y]

Thanks again for this info Jeffh, and it does make sense. Something I am for sure interested in trying.

My upstairs and my downstairs is 4 degrees apart at times...jeez.

How about air return? I noticed in the my oldest sons room his air return doesn't seem to be doing anything. I took the vent cover off and noticed he does have ducting but I don't know where it goes or how to get it to work...I think if he had proper circulation it would make a difference at least a bit to suck the hot air out.

[jeffh]

The return in houses is generally just an over-sized opening for air to make its way back to the furnace's blower. It is basically just a convuluded path that takes twists and turns through joist spaces and wall cavities. During construction, it is a bit hard to decipher what the path is, as the future drywall on the walls and ceilings help form sides to the cavity spaces. As long as it isn't blocked in a major way, I wouldn't be too worried about it. Your son's room may have an inadequate supply run in some fashion(undersized, long run, too many bends, or even broken fittings/pipe along the way). There may also be an abnormal heat load on the room as well(south facing, poor insulation, poor window seals, above hot garage, etc). If you were to just prop his door open, his room should have enough return air capacity as long as there is another unobstructed return grille nearby.

[Darkane]

Anyone have a source for Lennox parts?

They're generic I'm sure but I might need a start/run capacitor or even a fan motor.

Seems that my conderser unit is fine but the fan won't start. Compressor runs then trips (over pressure I think).

Capacitor looks fine however, doesn't look pregnant. Wondering if the contactor is gone - will have to use my VM on some stuff tonight.

[Darell_n]

Originally posted by Darkane
Anyone have a source for Lennox parts?

They're generic I'm sure but I might need a start/run capacitor or even a fan motor.

Seems that my conderser unit is fine but the fan won't start. Compressor runs then trips (over pressure I think).

Capacitor looks fine however, doesn't look pregnant. Wondering if the contactor is gone - will have to use my VM on some stuff tonight.

The condenser motor is usually fed from the compressor contactor. Does the motor spin freely by hand? I would measure the value of the capacitor and compare it to the labelled value, measure amperage going to the motor. (is it hot?)

[Darkane]

So after mucking around and checking stuff it turns out I got the fan going only if I gave it a kick start. I had to use a prop to initiate movement then it caught and spun up to full rpm.

I'd say my capacitor is shot then. Didn't have the juice to fire. Either that or a loose connection somewhere - couldn't see any.

Thanks for the response Darrell

[Darell_n]

Originally posted by Darkane


I'd say my capacitor is shot then. Didn't have the juice to fire.

x2.

[Darkane]

Back up and running.

Paid $52 from Arpi's for the new capacitor. I tried buying it from Lennox direct, they wouldn't let me because I couldn't prove my refrigeration ticket or mechanical ticket. I asked them if second class with half of my first was good enough and they said no haha. Oh well little do they know.

All said and done saved myself probably $200? What would a call out cost with replacement part?

[Maxt]

Originally posted by Darkane
Back up and running.

Paid $52 from Arpi's for the new capacitor. I tried buying it from Lennox direct, they wouldn't let me because I couldn't prove my refrigeration ticket or mechanical ticket. I asked them if second class with half of my first was good enough and they said no haha. Oh well little do they know.

All said and done saved myself probably $200? What would a call out cost with replacement part?
about 175.00
You should have gotten your bro to text me, it would have been $8.00...;)

[Darkane]

Originally posted by Maxt

about 175.00
You should have gotten your bro to text me, it would have been $8.00...;)

Damn! I didn't know mark up was that much :(

Thanks for the offer Max.