Air conditioner & heat pump controls & switches questions & answers.

This article series explains the function, location, identification & use of all air conditioning & heat pump system operating controls. Photos and text help you to find & recognize each of these controls and the text explains what the control does.

Q&A on Air Conditioning & Heat Pump System Operating & Safety Controls

These questions and answers about any and all of the controls and switches used with air conditioners and heat pumps were posted originally

at OPERATING CONTROLS, A/C & HEAT PUMP - topic home, be sure to review that article too.

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Question: HVAC wiring: wire size vs. circuit breaker size

(Jan 27, 2014) george said:

I am wiring a bryant 113a,21/2 ton ac unit. calles for 14 wire 46' run with a 25 amp breaker. My new run is 55'. Should I increse wire size or breaker size.

Reply:

(Jan 27, 2014) (mod) said:

It's always safer to use a heavier gauge wire than to put in a larger circuit breaker. For HVAC equipment, to handle the start-up surge in current draw, it is often permitted to install a one-step oversized breaker but before doing so take a look at the guidance in the installation instructions for your equipment and on the equipment data tag. And see

CIRCUIT BREAKER SIZE for A/C or HEAT PUMP

DATA TAGS on AIR CONDITIONERS

Question: HVAC circuit board trouble codes, lights, indicators

(May 4, 2014) Gary Althoff said:

Circuit boards trouble codes

Reply:

Gary I am guessing your succinct query asks for a guide to the trouble codes displayed by some HVAC circuit boards. I agree that such would be useful information. I've attempted to get at this question before for several readers and I find the subject too broad and grand for a single table or guide.

For obvious reasons the various manufacturers do not use standard indicator codes nor even methods of displaying them. We see individual colored lights, blinking light codes, digital codes, alphameric codes etc.

What we can do is dig up the error code guide for a specific brand and model of equipment.

Question: a repairman came into the wrong house (ours) and messed up our air conditioner

5/20.2014 Jennifer McCullough said:

A couple of weeks ago we found that our upstairs A/C unit was leaking water into our garage. At that point everything worked just as it should for heat and air. That is a small problem, but not the pressing issue here.

A few days later, an A/C repair truck showed up at our house saying he was here to fix the A/C and my kids let the guy in to look at it. The problem was that we hadn't called anyone.

The kids tried to contact me, but I was in a bad service area on my way home from work and wasn't aware he had even been there until I got home and he had already left. Apparently he fiddled around with the downstairs unit in the garage for about 20 minutes and supposedly called "me" and found out he was at the wrong address and left.

We didn't know there was a problem until later that night when it became icy cold in the house. Even when we turned the thermostat to off, it kept blowing cold air. We saw a switch on the actual unit in the garage and tried turning that off. It turned off the fan, but then the A/C wouldn't come back on unless we turned the switch back on.

Then we had a couple of days down in the low 40s and needed heat, so we turned the thermostat to heat and flipped the switch back up. I never felt warm air come out of the vent, and just like with the A/C, it wouldn't turn off. The actual thermostat still clicks as though it has reached a temperature to turn on or off, but the fan only blows according to the switch position. The upstairs heat and A/C work fine.

Do you think this misguided gentleman simply disconnected the thermostat from the unit or what, and how do we correct it without calling a service person to our house and spending who knows what?

The kids only saw green letters with A/C and Cooling Repair on the white truck...no company name or anything and the guy didn't give them a card. It will be near 90 later in the week and a working downstairs A/C would be great to have.

Reply:

Jennifer, as the Poughkeepsie police sergeant said to Anna M., a woman who complained about the night time noise made by train engineers blowing their whistle at crossings, Well that's one I haven't heard before.

Since the repair person actually did something to your A/C system and didn't take away anything from the home I'll assume it was a somewhat light-headed repair person at the wrong address. Indeed I once entered and began inspecting conditions in the wrong house.

I was joined by a termite inspector - we'd both been given a wrong address of a supposedly unoccupied home - by a realtor. Since two of us had come to the same address we never imagined we were in the wrong house. Luckily, soon and onlyt by noticing the names on mail lying out on a table did we figure out our mistake.

If there are only a few A/C repair companies in your area you could call around and in your least threatening tone (so as to get cooperation not defense) ask them to check service call records to see who was at your home on the date in question. Then if you can identify the company speak with the service manager and ask if he'd be kind enough to send over a senior technician to unfoul whatever was fouled up.

It sounds as if someone jury-rigged wiring or subverted a control.

(May 20, 2014) Jennifer McCullough said:

Thanks. Unfortunately I'm in metro Atlanta/Marietta, GA and there are hundreds of companies, so I don't even know where to begin.

I sent an email to a place that advertises around here to see if they recognize the truck. Beyond that I don't know what to do. We could probably redo the wiring if we knew where to start because it just seems like the thermostat isn't running the unit any more.

Reply:

Jennifer, if you don't have an idea who was there you're left with having to bring in an independent repair technician. Sorry.

If you want to check wiring of the thermostat, just disconnect the thermostat wires entirely - preferably at the A/C unit as that will exclude the chance of wires shorted together anywhere enroute from the thermostat to the unit.

With the thermostat disconnected you can be certain you're not calling for cooling. If the system still runs a control or control board has been snafu'd.

Question: AC compressor won't shut off

(June 20, 2014) Frank said:
my ac is working fine except that the compressor does not shut off. I have to turn off the breaker. Whats wrong.

Reply:

Frank,
Perhaps

Thermostat set below a level of cooling that the AC system can achieve, a short in thermostat wires, or a failed control or relay.

Question: A/C unit runs when oil fired furnace is running

21 April 2015 mark S. said:
my a/c unit comes on while my oil furnance is running any ideas?

Reply:

Mark:

On 2017-05-04 by (mod) -

Genie

At the top of this page we show a condensate overflow pan safety switch. This switch will turn off the air conditioner if it detects water (condensate spillage) in this overflow pan.

That's to prevent condensate from leaking into the ceiling below where it would cause damage and possibly an expensive mold contamination problem, and it's also to let the building owner know that repair is needed for the primary condensate disposal system.

On 2017-05-04 by Genie

What is the item in the first picture that is at the top of this page

On 2016-01-24 17:27:23.868377 by (mod) -

Check the service disconnect at or close to the outdoor compressor/condenser unit.

On 2016-01-24 06:16:06.498991 by mark

Power got shut off for 10 min and when turned back on I don't have heat. Everything blowing no heat someone said it needs heat pump breaker reset. Where is that. Rooftop Goodman unit

On 2015-09-26 20:55:08.332429 by craig

what can i do to determine if it is the control board or the relay. the thermostat was working at the time. the a/c works fine now, but am trying to get the heater working before winter comes. any ideas about how to troubleshoot?

On 2015-09-26 17:33:17.157934 by (mod) -

Craig:

I'm a bit confused by a repair that simply disconnects a wire. What the heck was the tech thinking? Forcing the heater "off" doesn't fix a problem with a control board or relay or thermostat that was turning on the heater when it should not.

Don't just wire it back up. In cooling mode the system should not be turning on the heater.

On 2015-09-26 17:06:59.246531 by craig

last summer, our a/c unit stopped cooling and was blowing heat. we contacted, we later realized was a parts changing service tech. he said he disconnected a wire on a relay and the a/c started working again. But we later learned because of this, the heater does not work. Our unit is a a/c-heat pump. I am trying to find the disconnected wire and/or the component he disconnected the wire from, but unable to. any suggestions? the unit is a Bryant. any help would be greatly appreciated.

On 2015-07-28 06:27:13.749365 by Anonymous

Jim,

If you listen at the outdoor compressor condenser unit you should heaer the compressor start and run, not just the fan.mitsmunlikely that a tech would leave a unit with fan on but no power to the compressor motor.

Search Inspectapedia for. REFRIGERANT LEAKS to see more advice that may assist in your case.

On 2015-07-28 02:47:28.840794 by Jim

Great site. I have a heat pump that is not cooling my townhouse. I know that both the inside and outside unit are most likely past their useful life but I was hoping to get at least a couple of months use out of it.

I called a service technician two weeks ago and he said everything was working "ok" but there was most likely a refrigerant leak. He suggested that I add some refrigerant and judge how long it lasts to determine how long I can continue to live with the system. I am not sure how much refrigerant he added but now the system cools worse than it did before he arrived.

The inside and outside unit both turn on but no cool air comes out, the temperature seems to be the same as when the fan is running. Is it possible that the compressor is disconnected but the outside unit's fan still runs?

I am getting follow up sales calls and I do not want to imply any impropriety about the compressor. Is the compressor a separate device and could be off or broken while the rest of the system appears to run? How can I check that the compressor is running?

On 2013-03-10 21:09:44.193882 by Anonymous

why iam not getting 120 volts on the black wire coming from the condensing fan motor that goes 0n the L1 on the contactor coil

On 2012-11-29 02:24:02.391183 by Mel

I have a heat pump in my house. Outside unit was replaced 7/2012 with a new Payne by Carrier.I live in East coast and it is winter time. I noticed that when condenser is on ,the inside fan doesn't turn on.

I called a contractor and replaced the motor in the air handler in the basement.But still, the outside unit turn on but sometimes the blower turn on sometimes not.I recall the contractor but they kept telling me that everything is fine .Sometimes it will take 10 min that the condenser is on before I feel that the fan is on. HELP! Need some advice

On 2012-09-03 06:42:53.447587 by Janet

I am looking for a users manual for A/C Vailant VD 105 HDO unit. The A/C is pre installed and it is a duct split system.

On 2012-08-14 17:43:17.307976 by aftabjamal

thanks for info god bless you

On 2012-07-27 20:47:11.308687 by (mod) -

Marc, I am grateful to see a question that is so far beyond my expertise, meaning guys smarter than me are helping with this website. I just don't know what you ought to see by way of voltage in the case you describe. I'd use the Arcoaire company's contact information to obtain the installation and service manual and wiring diagrams for the unit model and serial number you have installed. Or call their tech support hotline.

I can see why you're asking us - the company's website studiously and disappointingly avoids making it possible for a customer or anyone else to contact them directly: no address, no telephone, no email, no online documents except product sales descriptions and warranty information - often ten years. The company does provide a dealer locator web page and some specific dealer contacts (such as Precise Cooling Inc. in Port Charlotte Florida - (941) 626-6916) You should go to the arcoaire website to find the dealer closest to you. arcoaire [dot] com.

Please let us know what you find - what you learn will help other readers.

On 2012-07-27 20:39:07.963469 by (mod) -

Brad: because A/C equipment causes a brief current draw surge at the time of start-up of the compressor motor, installers are permitted to slightly "over-fuse" the system beyond its running current requirements. Usually the circuit wiring is sized to the running load amps not the higher value. For an authoritative citation start with the installation manual for your unit as doubtless it includes a wiring size recommendation.

Note this exception: for long wire runs it can become necessary to go to a larger wire size.

On 2012-07-25 01:47:04.707902 by Marc

Hi,
I have a 2 ton arcoaire hp with a scroll compressor. It just doesn't seem to be cooling correctly and I'm suspecting the control board on the condensor. The Reversing valve is supposed to be energized on a call for cooling and the correct calls are getting to the board. R-O-G have 25v on the input taps. If the valve is energized shouldn't the RV tap on the output side have 25v also? It shows 25 when the thermostat is set to off but nothing when set to cool. Also when I turn the system off it sounds like the valve is moving. It's kind of a deep sigh. I think it's always done that though. I just can't remember if it was when I turned it on or off. Any way to safely test the valve by jumpering to 25v? Thanks.

On 2012-05-14 04:27:40.473804 by Brad

I replaced an old Gaffers & Sattler 4-Ton compressor with a new Goodman 4-Ton (SEER 13) unit, but the city inspector is requiring that I replace the exisiting 10-gauge wiring with 8-gauge. He's going by the label on the unit which specifies a Maximum fuse size of 40 Amps. But the label also specifies a Minimum circuit size of 23.9 Amps, well under the 30 Amp current capacity of the exising 10-gauge wiring. To me it seems unreasonable to require larger wiring for a newer, more energy-efficient unit of the same size. What do you think?

On 2012-05-12 01:13:07.441953 by dan

I ordered a replacement contactor for my home a/c. The original part had A FLA rating of 25 and RES of 30. The new contactor has FLA 0f 30 and RES of 40. Can the new one be used?

On 2012-05-04 15:07:10.660880 by Anonymous

My compressor will not come on, it keep kicking off breaker . Do you think that could be the thermo, or the compacitor?

On 2012-04-17 00:28:00.783606 by (mod) -

Allan I wouldn't keep pressing the reset button if the system does not start and run on its own. If you are talking about the reset button on an electric motor, if it's going off on reset that usually means the motor is overheating or is unable to start (perhaps a bad start capacitor).

On 2012-04-14 01:20:36.949998 by allan

I have changed my thermostat and the transformer has electricity to all approiate wires but neither my central air or m,y heat will come on. if I go outside and push the reset button in and hold it the compressor works fine. what next?

On 2011-12-07 13:59:40.875617 by Bill

Does form installation have anything to do with the size of ac unit united needed for 3300 sqft coverage?

On 2011-09-03 18:38:12.708588 by (mod) -

If your heat is from different equipment (that is you have an air conditioner and separate heater not heat pump system) then it sounds as if heat works but your A/C does not. In that case take a look at the diagnostics beginning at LOST COOLING CAPACITY (article link in our ARTICLE INDEX)

On 2011-09-03 18:28:13.653871 by miche

i meant that the thermostat will turn the blower correctly for heat but not for cool

On 2011-09-03 18:23:31.516385 by (mod) -

Miche take a look at the wiring articles found under THERMOSTATS (link in our ARTICLE INDEX) for help in understanding the usual color coding on thermostat wiring.

Despite all those wires on your TT, it's basically an on-off switch. So when you pick the correct wire pair and join them you'd be doing the same as the thermostat in calling for cooling.

I'm not clear on what's meant by your heater will turn on the A/C system.

On 2011-09-03 18:14:04.332332 by miche

I can not find a model number on the control unit, best I can find is the number 960-130012. There are the following wires: yellow, red, white, green, blue. 24 AC power to control. When off 26 volts on red, when heat running 24 v on yellow, blue, and across temperature transistor

On 2011-09-03 18:05:09.743266 by miche

my bryant control unit runs both my carrier a/c and my water heater furnace. The a/c will not turn on the compressor or blower by temperature control, but my heater will. My Carrier compressor can be started manually by holding the reset button in and it puts out cold air. If this is a thermostat issue, how can I test it?

On 2011-08-23 00:58:23.395371 by Anonymous

Roy a bad start capacitor can cause a motor to run backwards.

On 2011-08-21 21:46:07.379503 by Roy Van

What makes the compressor run backwards on split outdoor unit

On 2011-07-06 17:09:44.609365 by (mod) -

Sue: try taking a look at the diagnostic article for air conditioning found among the links in our ARTICLE INDEX and titled
LOST COOLING CAPACITY

On 2011-07-05 21:56:20.009884 by sue

air conditioner doesn't keep blowing cold air just cool air so can't get room down

On 2011-06-27 04:12:14.035433 by Anonymous

Dave, how does the capacitor look in the outside unit?? some of the calls ive gone to have the same systems.. and usually a bad capacitor will cause that effect

On 2011-06-23 12:25:39.601451 by Dave

when I turn on the unit to cool, the inside unit will turn on but the outside unit will not. The contactor is good, but something is weird with the 24v supply. Something blew the fuse in the board on the inside unit. Replaced the fuse and worked for awhile. Any thoughts. Thanks

On 2011-05-31 18:08:14.806741 by (mod) -

Sounds like a short circuit

On 2011-05-31 18:03:46.744921 by e burke

110volt to 24volt transformer blows. 24 volt wiring seems to be ok. anyone have an idea for us to check? thnx

On 2011-05-03 14:58:49.263478 by (mod) -

This sounds like a control board or control circuit problem. You need to call an air conditioning or heat pump service technician.

On 2011-05-02 20:49:00.145974 by wayne strickland

compressor not getting signal from thermostat. compressor keeps running when thermostat is set to turn off. to turn off compressor, the circuit breaker needs to be turned off to stop compressor from running. when thermostat is set to run, the compressor won't run. the main circuit breaker has to be turned on to start compressor to run.

...

Continue reading at OPERATING CONTROLS, A/C & HEAT PUMP or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR HANDLER / BLOWER UNITS - home
• COMPRESSOR / CONDENSER REPAIR - home
• CONTROLS & SWITCHES, A/C - HEAT PUMP
• COOLING & HEATING CONTROL & SWITCH INDEX - index to all controls
• DIAGNOSTIC GUIDE A/C or HEAT PUMP - suggestions for diagnosing compressor or condenser fan and coil problems that can mean intermittent or totally lost cooling capacity of your system.

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A/C & HEAT PUMP OPERATING CONTROLS FAQS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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