HVAC system control & switch Questions & Answers set #2: what are the various HVAC switches and controls, where are they found, what does each do & how do we repair or replace a bad control?

Page top photo: outdoor service switch on the brick wall allows the service technician to safely turn power on and off while working on the compressor/condenser unit.

But this one used copper pipes where fuses should have been installed - a very dangerous condition.

This article series explains where to find and how to use the switches and controls for air conditioning and heat pump systems.

Air Conditioner Switch & Control FAQs

These questions and answers abour air conditioner and heat pump controls and switches were posted originally

at CONTROLS & SWITCHES, A/C - HEAT PUMP where you will find a discussion of thermostats, zone dampers, and circuit breakers on air conditioners and heat pump systems.

Air conditioning and heat pump diagnostic procedures are at DIAGNOSTIC GUIDE A/C or HEAT PUMP

First here are some helpful A/C and heat pump diagnostic procedures:

Question: My Air Conditioner won't turn off - what to do?

Carla said: My outside air unit will not turn off on its own. I have to manually turn the breaker off to turn it off. Does anyone know why or how I can fix it?

Reply:

Carla if your A/C won't turn off it could be that the thermostat is set to a temperature that the system cannot reach - due to lost cooling or due to a setting below the capability of the system.

If your A/C won't turn off even if you set the thermostat to a temperature that is above the current room temp, then the thermostat or an A/C control board or switch is bad and needs replacement - in that case you need a service call from a trained HVAC Technician.

See OPERATING TEMPERATURES HVAC and also CONTROLS & SWITCHES, A/C - HEAT PUMP

When your air conditioner ultimately turns off but is staying on too long, see LONG-ON CYCLING AC COMPRESSOR.

Question: My Air Conditioner (or heat pump) keeps cycling on and off too rapidly - what might be wrong? short A/C on-cycle problems

Joe said: short cycling air conditioner compressor diagnosis: I have the same problem as Mathew: my A/C compressor cycles on and of every ~10 seconds. I is about 5yr old. What can we do to fix this system. Please help. Thanks!

Matthew said: short cycling air conditioner problems: Our air conditioning compressor cycles on and of every few seconds or minutes. What can we do to fix this systems not even a year old

Reply:

See SHORT CYCLING AC COMPRESSOR for details of diagnosing and repairing an AC unit that keeps cycling on and off

Heat works but Air Conditioning Doesn't - Where's the control relay?

I have central air conditioning . and heat.. Heat works air conditioning don't. I have been told it could be relay switch. Where is relay location - - Tom

Reply by (mod) -

Typically there are relays inside the compressor/condenser unit and often in the indoor air handler compartment as well, usually on a circuit board.

But Watch out: That's a service item for your trained service tech, not a homeowner replacement part.

Outside condenser fan doesn't run but I have heat indoors: is something wrong ?

Hi, my outside unit fan does not turn on but i do have heat coming through the vent and the green comes on the thermostat. by Doumbia

Reply by (mod) - your system may be running in backup heat mode

Is your system running in backup heat mode? if so that's normal. If outdoor temperatures are very low I suspect that's what's going on.

Where is the Cut-off Switch for my LG Portable Air Conditioner?

Where is the cutoff switch for my LG Model LP1414GXR? - Danny

Reply by (mod) - LG portable AC remote control

Danny

The LG Portable Air Conditioner you cite uses a remote control for its operations.

If you've lost your remote or need a user's guide, contact LG:

LG Electronics U.S.A., Inc.
1000 Sylvan Avenue Englewood Cliffs, NJ 07632 Customer Service and Technical Support: (800) 243-0000
LG.com

A/C circuit breaker keeps clicking off.

My air conditioner runs great but the circuit breaker keeps clicking off. It may run for several hours before clicking off and usually I trip the switch and it comes back on, however every now and then when I click the breaker back on it fails to work. Once waiting a several minutes it starts again when I click the switch.

I replaced the circuit breaker but it did not fix the problem. I have blown out the radiator coils so it is not blocking air flow. I am at a loss. I have replaced the filter. I would appreciate any suggestions. JRB

Reply by Anonymous

JRB

Watch out: It sounds as if your AC circuit is drawing excess current - something is failing, probably a motor. Watch out: don't keep running it or you risk as fire.

Kenmore A/C fan runs slowly and compressor won't turn on

Thank for your informative post. I Have a Kenmore AC unit outside, the fan runs slow and compressor doesnt turn on. I replaced the capacitor and the compressor still doesnt work. Any tips would be greatly appreciated - by Jay -

Reply by (mod) -

Jay the service tech, in addition to checking for a bad control or relay or board or wiring, will perhaps check the current draw to look for a seized motor.

Indoor blower runs but outdoor split system compressor/condenser does not turn on

My blower comes on but split unit outside does not. I have replaced capacitor. I can manually push in something that looks like a breaker in side unit (below and to the right of capacitor) and unit will come on as long as I hold it in. On 2015-06-14 by Anonymous -

Reply by (mod) -

ANON

try the diagnostics beginning with the article (Found in INDEX to RELATED ARTICLES at our Continue reading suggestions at the end of this article)

COMPRESSOR / CONDENSER REPAIR - topic home, problems with air conditioner compressor/condenser units

Air to air heat pump that pops the breaker

I have an air to air heat pump that pops the breaker in the cord when changing thermostat the heat.The system works fine in cooling mode when removing the unit from the wall the 4 way valve made some strange noise . Is the power draw on the 4 way valve strong enough to pop the breaker? Mike

Reply by (mod) - air to air heat pump that pops the breaker

Mike

If the unit is switching to heating mode I suspect a control board or heater element failure.

A failing compressor motor will also trip the breaker.

Followup by Anonymous

Thank You for the feed back it was very helpful

Will it hurt the unit if I force the spring loaded switch together and let the unit run

RE posted from mobile site

AUTHOR:Kevin klinglesmith (no email)

COMMENT: Will it hurt the unit if I force the spring loaded switch together and let the unit run

Reply by (mod) - Holding down a relay to force equipment to run is unsafe and so not recommended for homeowners

Kevin

Techs do this as a test and only BRIEFLY.

Watch out: I would never force equipment to run by holding a relay closed - doing so risks overheating a control or component and thus a fire or other damage.

And if you're not trained in HVAC system repair you could be shocked or killed.

A/C won't work after plumber came to unclog a sink drain where the A/C condensate goes

The plumber came and cleaned out a drain from the a/c that runs into one of my sinks because the sink was clogging up.

Now my a/c doesn't work at all and it was fine the same day of him doing that. Now an a/c man tells me that is the circuit board needing to be replaced! by Laura

Reply by (mod) - last person to touch the equipment will be blamed for its failure

Laura

I don't blame you for being baffled. I call this "the last person in" syndrome. Service techs know that the last person to touch the equipment will be held responsible for its next failure.

Sometimes justly, sometimes not. In this case, if the plumber never touched the A/C system, just the sink drain, I would not think she or he had a thing to do with the air conditioning system.

Possibly the fault showed up because the system began to get used?

Details?

Followup by Laura

The plumber did go into the attic and told me that he would be vacuuming/cleaning out the drain from the a/c that drains to the sink. And being from Texas we do use a/c mostly year round. The a/c will not work at all.

Reply by (mod) -

Aha
so let's take a look: did he

- bang into something
- spill anything
- turn any switches on or off
- disconnect anything

As a simple example: if your AC system has a condensate drain pan safety switch that was disturbed, that alone could have switched off the AC unit.

 

Question: air conditioner keeps cooling even in heating mode

hi I have a problem with window type air conditioner, it is cooling even when I have turned the adjuster to heating mode. it only cools and regrets to warm me up in my office - Justice

Reply from Dave:

DAVE said: What does it do Justice?

Justice,

Dave and I face the difficulty of guessing at what's wrong on an air conditioner with very little information.

But I'll add that if a unit will not change from cooling to heating mode, and presuming it is designed as a heat pump capable of both cooling and heating, then an internal control or switch needs repair or replacement - possibly the reversing valve in the unit.

See REVERSING VALVE on HEAT PUMPS

 

Question: air conditioner fails in bad weather

(June 28, 2014) terry wycoff

i have an old arcla? brand ac that runs water outside,but as soon as you turn the dial only runs seconds

(July 28, 2014) Anonymous

Hi. I have brand new American Standard split system. Runs fine until there's a storm. Power doesn't need to go off, nothing weird happens in the house, but the unit loses all power, even the thermostat is dead, which is wired to the air handler in the crawl space.

I've had utlility company out and everything on their side is good. I've had electrician out and all on my side is good. Unit is under warranty for now, but I'm frustrated.

I have to call them out on average once a month when a storm goes through. I have two other places and this doesn't happen, ever. Was thinking about installing whole house surge protector, but both air guy and electrician tell me that won't help my problem. This is not good and I need some type of idea on what to do. I'm really upset, since my air company can't seem to fix it. Thank you.

Reply:

I agree you need better diagnosis, and from here can only guess.

Has anyone checked for a water or moisture problem in controls or wiring?

Question: service panel got wet, mother board got wet, green light not working

I left my service panel off and the inside of it got wet. The mother board had a green light that is not working. The unit does not come on at all. What should I do about it to fix it. - Bov

Reply:

Bov

I'm troubled by the water damage too and can't begin to tell you how to fix it - knowing nothing about your system, what it is, what got wet, or what are your skills.

There is risk of further equipment damage just from turning it on if the controls got wet.

I'd ask for help from an experienced service tech or electrician both for safety and to avoid frying more components or getting shocked.

Question: air conditioner trips circuit breaker

Air conditioner wont run it will kick the house breaker out when you turn the power on (May 10, 2014) William

Reply:

Watch out: William, leave the unit off. The problem could be a bad compressor - we don't want to damage other components or overheat wiring (a fire hazard) by trying to run it.

 

Question: American Standard Heritage 16 Heat pump operating trouble

8/18/14 sleepless in Seattle cause no cooling

I have an American Standard Heritage 16 Heat pump. I did the terrible deed of not cleaning the air filter located above furnace and it shut off the whole system. I cleaned the filter and ran through some test modes on the thermostat and the furnace comes on fine, but not the heat pump.

I read that a motor may have a reset button that needs attention, but I opened up the side of this thing and it looks like a motor covered with orange insulation is under the fan, but I can't see how to get to it. Yes. I know nothing about this stuff but can read directions, only I'm not able to get any schematics on this thing. Any help would be appreciated.

Reply:

Sleepless - Seattle

We're flying blind here but possibly a fan motor might overheat due to reduced air flow. However If the furnace and blower run in response to a call for heat then the fan motor is working. If the fan is inoperative the furnace limit control should shut the system down.

I'm not sure how an indoor fan problem will keep an outdoor heat pump from turning on. I'd look for a thermostat mode setting problem or a control board or relay problem first.

Reader follow-up:

The furnace fan comes on during test mode from the thermostat. Once the thermostat calls for heat or cooling, it shuts off and heat pump does not come on. Thermostat flashes "wait" like the heat pump is in some setup or testing mode?

Reply:

If the blower runs properly in test mode then we're not looking at a problem with the blower fan motor itself. More likely there is a problem with the compressor/condenser unit or a control board, relay, or theremostat problem.

First check your thermostat's instructions and manual. Some therm air conditioner and heat pump thermostats such as some Honeywell models will introduce a five-minute delay before starting the compressor when the thermostat is switched "on" or set higher in short intervals.

That's because rapid turning off and on of a call for heat at a thermostat can cause compressor motor short cycling.

Because some compressors may have trouble starting against high refrigerant head pressures that remain at the moment of switching "off" the five minute delay is intended to give time for refrigerant pressures to equalize in the system - giving an easier start to the compressor. If the compressor still won't start I'd suspect a bad start relay or start capacitor.

It's time to ask your HVAC service company to send out a trained service tech.

 

Question: furnace fan comes on in thermostat test mode - flashing "Wait"

The furnace fan comes on during test mode from the thermostat. Once the thermostat calls for heat or cooling, it shuts off and heat pump does not come on. Thermostat flashes "wait" like the heat pump is in some setup or testing mode? Sleepless in Seattle

Reply:

If the blower runs properly in test mode then we're not looking at a problem with the blower fan motor itself. More likely there is a problem with the the thermostat itself, or more troublesome, the compressor/condenser unit or a control board, relay.

First check your thermostat's instructions and manual. Some therm air conditioner and heat pump thermostats such as some Honeywell models will introduce a five-minute delay before starting the compressor when the thermostat is switched "on" or set higher in short intervals.

That's because rapid turning off and on of a call for heat at a thermostat can cause compressor motor short cycling. Because some compressors may have trouble starting against high refrigerant head pressures that remain at the moment of switching "off" the five minute delay is intended to give time for refrigerant pressures to equalize in the system - giving an easier start to the compressor.

Watch out: five minutes may not be enough - depending on the brand and model hat pump or compressor.

At REFRIGERANT FLOODBACK, LIQUID SLUGGING we explain how liquid refrigerant entering a heat pump or air conditioner compressor motor can destroy it and we discuss the recommended time that the system should be LEFT OFF if was switched off while it was running

If the compressor still won't start I'd suspect a bad start relay or start capacitor.

Sleepless - Seattle said: bad thermostat

Service tech said the thermostat (Honeywell) is bad, but still under warranty. Yay!
Thanks for your help.

 

Question: Florida Heat Pump - not working in heating mode

(Feb 5, 2015) T.P. said:
Hey folks, I've got a well used Florida Heat Pump. During the winter, about 4 times/week, the air suddenly blows cold.

We found that stopping the heat (on the thermostat), and restarting it seems to "reset" the system, and after a few minutes delay, it returns to normal temps. Any idea what might be going on? Thanks.

Reply:

Sounds as if your heat pump is not heating: perhaps the thermostatic expansion valve is freezing-up.

Less likely, a control board or relay problem. Ask your service tech to check out the system. Keep us posted.

...

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

Or see A/C HEAT PUMP CONTROL / SWITCH FAQs-3 - more questions and answers about switches and controls on air conditioners and heat pumps.

Or see these

Recommended Articles

• A/C - HEAT PUMP CONTROLS & SWITCHES
  • OUTSIDE HVAC SWITCHES & CONTROLS
  • INSIDE SWITCHES & CONTROLS
  • OPERATING CONTROLS, A/C & HEAT PUMP

Suggested citation for this web page

A/C HEAT PUMP CONTROL / SWITCH FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

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

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.

---

IF above you see "Comment Form is loading comments..." then COMMENT BOX - countable.ca / bawkbox.com IS NOT WORKING.

In any case you are welcome to send an email directly to us at InspectApedia.com at editor@inspectApedia.com

We'll reply to you directly. Please help us help you by noting, in your email, the URL of the InspectApedia page where you wanted to comment.

Citations & References

In addition to any citations in the article above, a full list is available on request.

---

ADVERTISEMENT

---