Weak A/C or Heat Air Flow FAQs

Questions & answers on weak supply air flow from an HVAC cooling or heating system

Weak air Flow traced to Clogged Air Filters: Can Clogged Air Filters Also Affect the Room Thermostat?

If air conditioner filters are clogged will it cause the thermostat to shut off? Jim

Reply:

Jim: clogged A/C filters won't cause a room thermostat to shut off. The thermostat responds to room temperature.\

However clogged A/C filters that reduce air flow, cause coil frosting, or otherwise reduce or stop the flow of cool air into the room where the thermostat is located would mean that the thermostat would remain "un-satisfied" and should mean that the thermostat says "on" - continuing to call for cooling.

See AIR FILTERS for HVAC SYSTEMS

 

Our A/C unit is not drawing air through the return air inlet and filter

A/C unit does not have intake suction from inside of home where filter is located. - by Anonymous

Reply by (mod) - air conditioning system has NO return air taken from inside the home

Anonymous

If you are saying that your air conditioning system has NO return air taken from inside the home, that's not a reasonable design - too costly to operate;

If you are saying that there is no air flow in to the return air inlet, then I suspect there is a dirty filter or a duct disconnection or leak problem to find and fix.

So what's needed is

1. Check for a dirty or blocked air filter and replace it with a new clean filter

If that doesn't fix the problem then

2. Call your HVAC service company and ask for diagnosis and repair help; you may need to have the blower fan cleaned or there could be a duct system that's blocked or disconnected, or the blower may not be working at all

- Daniel

To Improve air flow I ran the A/C system with no air filter - how can I fix the system?

Just got done replacing my condenser fan motor and capacitor...finally I have cold air again.

Removed the filter from the inside unit as it was dirty but didn't have a new one, so let it run a few hours with no filter.

Two rooms in my house have always been 'hot' due to low airflow from the registers, but just dealt with it for many years. (I have tried both expensive, cheap, reusable filters - same result.)

I checked the airflow from these registers (with no filter in place) and there was GREAT airflow, and the rooms were both quite cool.

I bought new filters and installed one, then checked airflow in these rooms again.

As always, very poor airflow.

Since my electric bill was $400 this month (of course it's the hottest June in Colorado on record) I'd like to help with it's efficiency.

So, my AC has restricted airflow when the filter in place, and my AC is working harder than it needs to.

What, if anything, can I do to help this situation? I certainly can't go for long without a filter...any advise is appreciated. by Mike -

Reply by (mod)

@ Mike

Watch out: running your A/C or heat pump system without an air filter will cause both the blower fan blades and the evaporator coil itself to become dust clogged. Ultimately that blocks air flow and will require a service call to clean the system properly.

Once that hsa been done:

I would look into replacing the filter with a more flow-efficient type that would increase the airflow and still provide proper air filtration .

It could be that you are using HEPA rated filters rather than standard filters, and if you dont need the HEPA rated filtration you could quite nicely do without it...

Aside from that option, replacing your fan or blower unit may prove feasible.

It may be that your current fan or blower is dying on you or you just need a more powerful unit to blow air through thick air filters (especially if you are using HEPA filters and you need to keep them for health concerns...)

AC was getting weak. We shut it off over-night. In the morning it was working.

AC was getting weak. We shut it off over-night. In the mourning it was working. Kept apt. with tech that we made the day it stopped.

He sucked water out of the PVC drain line where condensate discharge water comes out from the AC.

3 weeks later, AC blowing warm air again.

Tech came, showed me the condenser(?) - (that small can about the size of a 6oz drink) was swollen.

New condenser(?) installed & it worked again, for a week. Now it stopped blowing cold air again. All three times it rained heavy.

Made sure the water from the unit can get out since I suspected rain water might be preventing the run-off water from the AC unit to get out.

Also sucked it with a shop vac. This time and previous, fan in the compressor (the lager unit outside) was not rotating. The first time it was shutting off & on in approximately 5 minute intervals. What's causing this? could wrong amperage (but I did not change anything) blow the condenser?

Could water short-circuit the unit?

If so, why did this not used to happen but is now? It ran fine during hurricane Irene. by Irene

Reply by (mod) -

Irene,

First: check your air filter:

When the air flow is weak but returns strong after the system has been shut down for hours the most-likely explanation was that the cooling coil (evaporator coil at your indoor air handler) was blocked by frost or ice - as can happen if there is a refrigerant leak or if the system was run without a good air filter.

Next: understand the repair that was already made:

What you refer to as the "condenser" that was swapped out was probably a start/run capacitor - an electrical component.

Often a new capacitor can get an iffy electrical motor running again by giving it an extra electrical "kick" to get spinning. But if the motor is fundamentally failing, say by a bad internal bearing or some other problem, eventually even the new capacitor won't get it working. The bad motor will need repair or more likely, replacement.

At your outside A/C unit listen to hear what's happening - if you hear a humming there is a motor unable to start.

When a fan won't start we suspect a bad start/run capacitor for that motor, or a bad fan motor or bearing itself.

The condensate drain problem is a separate issue.

 

What are the Standards for Air Conditioning System Cooling Capacity or capability required for rental units?

My rental property management agency told me that my unit's AC capacity is only required to cool my townhouse (1800 sq ft) to 15 degrees below the outside temp. Is that correct? I don't believe them. - by Brent

Reply by (mod) -

Brent:

On Standards for Air COnditioning System Cooling Capacity or capability required for rental units

There is no national code or standard for the cooling capacity nor turn-on date for air conditioning in rental units, though there may be state or local housing authority standards for cooling in your municipality - that's something for you to ask your local building department or rental housing authority.

Indeed if a cooling system is under-sized it is likely to be unable to keep up with cooling your rental unit in very hot weather. The actual ability of an air conditioner to cool an occupied space is of course affected by the properties of the building as well as the air conditioner.

So picking an A/C unit's BTU cooling capacity, normally based on square feet alone, can get us in trouble if the particular building has lots of sun-exposed windows, or other reasons for high heat gain.

Certainly in our research to answer your questions we found some municipalities where there is a local rental unit housing authority to whom complaints should be addressed if a landlord refuses to respond to an air conditioning operating problem in a reasonable amount of time.

E.G. quoting from Montgomery County Maryland:

To file a complaint, please provide a brief description of the problem, the address where the violation is occurring, along with a specific location (if applicable).

The caller's name and phone number are requested so that the inspector can call and provide an update of their findings or, if this is a rental property, to schedule an appointment.

Weak air conditioner air flow - is there a relationship between refrigerant charge level and weak cool air flow rate?

Les said: Weak air conditioner air flow: Our A/C was serviced two months ago and the repairman said it had a leak.

$400 later it was recharged with coolant and now the ac is doing the same thing. Very little pressure coming out of vents and no cold air coming out. Does anyone know what I can do for the weekend? It is stifling!

See DUCT & AIR FLOW PROBLEMS

Reply by (mod) - no

Les:

Watch out: A leak that was fixed by a re-charge is not as good a repair as a leak that was fixed by finding and fixing the leak - you'll just have to keep adding refrigerant.

Watch out: weak air flow out of the vents would not be due to a refrigerant leak; more likely a clogged filter or crushed or disconnected ductwork, or a blower fan problem.

Blower fan runs but air flow is weak: How do I improve airflow or air delivery from an HVAC system?

I need to move more air through the duct system. I have a 1075 CFM unit now - can I replace it with a 1110 CFM or large with no problems - by Danny P Verrette

by (mod) -

Danny, in general it is often possible to improve airflow or air delivery from an HVAC system by several means, but if you push air too fast you may exceed the capacity of the cooling coil.

Also, before increasing fan capacity I would want an accurate assessment of the system.

For example, if the present air delivery rate is too weak, we want first to be sure the filter is not clogged, ductwork not blocked, crushed, leaky, disconnected, registers are open, return air is adequate. Otherwise your "fix" may be both wrong and ineffective.

See our complete guide at

AIR FLOW IMPROVEMENT, HVAC

Air flow is cool but weak at supply vents

Question, just had and HVAC tech over. The fan is working and the freon level isn't the issue. Low air flow coming from the vents and it is cool, but weak flow.

The pipe has ice on it when running and he suspects it is a blockage/resistance to the coil.

Is there a fix outside of replacing the whole unit ($11,000). Could it be anything with blocked/detached ducts?

Can a blockage to the coil be fixed? Thanks. Tom

Reply by (mod) - Is there a fix other than replacing the whole A/C unit ?

I would not consider replacing the "whole unit" unless it's very antiquated;

I've seen the air flow rate double or triple simply from cleaning the blower fan - a small bit of debris greatly reduces the fan output;

And I'd really be upset if I spent $11K on a new AHU and heater or A/C unit only to find that the original problem was a crimped, fallen, or damaged air duct. So let's inspect the whole duct system with care.

If the coil is "blocked" itself that's normal and occurs as dust and debris accumulate on the coil fins (maybe because someobody forgot to install the air filter in the system); coil cleaning service is a normal and common service procedure and costs a micro-fraction of a new system.

The only rub is if the system is very old and the coil very corroded the tech may be afraid to spray on the cleaner; (Spray, wait, vacuum up the muck).

What to check if no air comes from any of the vents but the blower is running

If there is no air coming from any of the vents in the apartment and the indoor blower is running, you should check the : breaker,condensing unit,fire damper,owners manual - Johnny

Reply by (mod) - check for crushed or disconnected ductwork

Thanks Johnny

I would add a check for crushed or disconnected ductwork

 

No Airflow: condenser froze because I had shut down the blower while the AC was still running

A few days ago I had to trip a couple of fuses to install a new light in the hallway.

What I forgot to do was to shut the AC off while I was doing the work.

What happened next was that my condenser froze because I had shut down the blower while the AC was still running.

The condenser had accumulated so much ice that my duct system was about 80% blocked.

Had to start the heater to defrost the condenser and then set the temp bakdown to AC levels. On 2018-05-28 by Sam Manz

Reply by (mod) -

Sam

Thank you for your report of this experience. It will certainly help other readers. Your system should be okay once you defrost of the coil. Let us know what happens.

Only getting cold air pressure on one side of mobile home

Only getting cold air pressure on one side of mobile home, replaced cross over and looked down in every register vent with mirror and light and it's clean from front to back on both sides and still no pressure but the side that works blows hard. Please I'm going nuts. - by Kristie

Reply by (mod) -

Kristie

There may be a balancing damper closed somewhere - follow the ductwork from the point that the two sides of the home's air system split off - look for a damper lever or motor.

Does my couch block return air intake?

Is there any way that my couch is blocking the intake with this amount of space? Our motor has burnt out twice this summer.

The repair crew said this wasn't enough space and was the cause of the motor burn out.

The first motor worked for 2 years until breaking and the 2nd broke only a month after installation. Is it more likely that this is an electrical issue or is this really blocking intake? - by Joey Weng

Reply by (mod) -

I suspect there's some other issue, Joey. You've got a reasonable amount of room in front of the return air inlet.

A blocked filter or blocked return air duct might overheat the system. But I don't see that in your photo. Of course there could be an air flow blockage elsewhere in the duct system or even something as simple as a blocked dirty air filter or a dirty squirrel cage blower fan itself.

The service tech can certainly also check supply voltage and wiring.

Evaporator fan motor runs very slowly - slow fan means weak air flow at supply registers

System was working fine during cooling mode, we use gas heat and barely use the heat setting. when the weather started warming up, we turned on the cooling setting, but the evaporator fan motor runs very slow.

Side panel off and you can see the fan turning very slowly, input wire has 20 volts. Any help is appreciated. - by Dan

Reply by (mod) -

Dan

Seeing just 20VAC on a fan circuit that normally runs at 120VAC, particularly if the input voltage to the unit is found to be proper (120VAC) suggests a bad wiring connection (corroded or a loose electrical splice) or control board or relay.

There could be a low-voltage short in the unit's wiring.

(Look for damaged wires, corrosion, or poor-quality after-market repair parts).

But most likely is a bad fan motor.

LG Air Conditioner in Singapore is Not Cooling our Rooms

My LG aircon out door unit is working but no cooling in rooms. Model is H2UC186FA0
Kindly advise what could be possible problem.

Can I get schematic for outdoor unit as well. Thanks a lot.- Shan in Singapore.

Reply:

Shan

If the air handler is moving air but the air is not cold most likely the outdoor compressor/condenser is not working.

See the diagnostics above on this page - AIR FLOW TOO WEAK

For more broad diagnostic procedures see

• 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.

About a schematic, I too found it difficult to locate a service manual for your unit - I went to LG's support website at lg.com where the H2UC186FA0 is indeed listed, but the company says that no technical manual is available - which was a surprise.

Here is a link to the LG service manual for the H2UC series split system air conditioners

LG HVAC SYSTEMS INFORMATION & MANUALS

or go directly to the LG HVAC SYSTEM SERVICE MANUAL [PDF] at

You can contact an LG Support Representative at

1 800-822-822(National call Rate)

AC tripped fuses - iced coil

A few days ago I had to trip a couple of fuses to install a new light in the hallway.
What I forgot to do was to shut the AC off while I was doing the work.

What happened next was that my condenser froze because I had shut down the blower while the AC was still running.

The condenser had accumulated so much ice that my duct system was about 80% blocked.

Had to start the heater to defrost the condenser and then set the temp bakdown to AC levels. by Sam Manz

Reply by (mod) -

Sam

Thank you for your report of this experience. It will certainly help other readers. Your system should be okay once you defrost of the coil. Let us know what happens.

What should the air speed be at supply vents?

What is the ideal speed air should exit a vent? - by Mark

Reply by (mod) -

Mark

Thanks for asking a critical and very basic question: what should the air flow rate be at a supply register?

If you are cooling your home, the desirable rate of cool air flow in an air conditioning system is around 400 to 450 cubic feet per minute.

Larger air ducts routed only through conditioned space might work better with a still slower air speed in fpm.

But

Watch out: that is NOT necessarily the "right answer" for your home. There are some important and very basic variables that I'll state in a more-detailed reply.

Please find your question and my detailed reply now at the bottom of

AIR FLOW RATES in HVAC SYSTEMS

Will reducing the diameter of our supply duct improve the air flow in the system?

I have a 12 in. Round flex return from the outside system to fixed duct. Can I reduce this to a 10 in. In order to improve air flow throughout the system? This is a manufactured home, 1000 sq.ft. . The central air is less than 2 yrs. old, flex ducts are not crimped or ripped.

There is air flow to all returns, but I would like to increase air movement. - by David Krucz

Reply by (mod) - NO

I don't think so David. Reducing the diameter of return duct will restrict air flow significantly. It won't improve it.

Start with a clean air filter and with cleaning the blower squirrell cage fan; inspect the ductwork for kinks or blockage.

Then search InspectApedia using the search box at the top or bottom of any our pages for heating or cooling air flow improvement or start reading at

AIR FLOW TOO WEAK - topic home and also be sure to read

RETURN AIR, INCREASE

Can I block some air supply registers to get more airflow out at other rooms?

the Master Bdr is on second floor with HVAC unit in heated/cooled basement. There are Three other bdr son second floor. Can I block some registers on the first or second floors to increase air flow to the Master Bdr. The Master has three registers and two returns. - by Bill_Thomas

Reply by (mod) - yes

Yes you can do that as long as the other rooms remain habitable.

One side of house has great airflow, the other almost zero

I just moved into a home with a decent AC system. The left side of the house (living room, front room, master bedroom and bathroom the ax vents are loud, have massive airflow and cold.

The right side of the house (three other bedrooms) the ac vents blow very very weak and it doesn't seem as cold as the other side of the house. What can it be?

My two boys bedroom are warm as hell when me and the wife are freezing.

The thermostat is set to 75 and it's located by the three bedrooms on the warm side of the house and it seems to have a hard time going below 78 at times. Very frustrating! Any help will be greatly appreciated! - by Andre

Reply by (mod) -

Andre,

I would first confirm that all of the ductwork is intact and properly connected. If there are no. Problems then I would had a balancing damper to help redirect air flow to the weak side

Half our doublewide gets good air flow, the other half gets nothing

I live in a seven year old 1600 sf double wide with a heat pump .

Half of the registers in the home provide excellent air flow no matter if I am heating or cooling while the other half of the registers provide little to no air flow at all .

Any suggestions on what I need to check . Thank You . - by Jeff in NC

Reply by (mod) -

I would get under the home and follow the HVAC ducts from the air handler onwards - guessing that as usual ducts are under the unit. You'll probably find a point at which the main line splits into two: one going to each of two halves of the home.

From that point onwards along the half of the home with poor flow you'll find the trouble: a blocked, crimped, or disconnected duct or perhaps an improperly set balancing damper.

Followup by Jeff in NC

Thank You . I'll give that a try .

I need to replace our A/C system because air flow is so weak

Uggg SO annoyed. I have serious sinus issues and if its to dry and a/c isnt cooling enough BAM sinus infection.

I checked the vents after cutting the air down and air is coming out but barely. I know we prob need a new unit by now but we are bleeding money right now with my wifes medical problems. by AIRnnoyed

Reply by (mod) - do not replace air conditioning equipment if the problem is too low air flow.

I would not replace air conditioning equipment if the problem is too low air flow. Usually that's something that can be corrected by finding and fixing a problem in the ductwork or a dirty air filter or a dirty blower fan.

I can only run one heating zone at a time or we don't get enough heat

I bought a townhome built in 2014 a little over 1600 sqft, It runs off a dual zone control system.

My current problem seems to be that I can only run 1 zone at a time efficiently. Like now for example its cold here and if I have both thermostats on the house will despite the temp setting the house will stay cold and little air can be felt coming from the vents.

BUT if I turn of 1 zone the air blows strong and heat up that zone efficiently. Same goes for cooling. I'm getting tired of switching either zone off depending on where I am in the house to be comfortable. Can you advise on this? - by Andre A.

Reply by (mod) - start by looking at the zone dampers

Andre

Your HVAC service tech will perhaps start by looking at the zone dampers to see if they are opening as they should be, then at the air handler to see if the blower fan is running and clean, and also to confirm that the air handler blower capacity is properly sized for the duct system

Oversized heat pump doesn't have enough return air

contractor put an overkill size heat pump in my rental mobile home.

it is only a little over 800 sq. feet. all the duct work was replaced and an air handler was installed as there was a split previously being used. strong air flow from register vents but weak air flow on return vent where filter goes.

unit does cool properly in hot weather until late at night nor does unit heat properly in cold weather.if it is 25 degrees it will only get 63 in house. by john

Reply by (mod) - not enough return air

John,

It sounds like you've diagnosed the first problem, not having enough return air. If you checked the return ducts and everything is connected and tight end not leaking then you may need to add additional return air

Watch out though, when you get the return and Supply Air balanced, if the air conditioning system is in fact oversized you may find that it cools but it does not de humidify.

See RETURN AIR, INCREASE

Refrigerant leaks, coil ices up, cool air isn't being delivered

We have a dual zone HVAC. We just had it serviced with 2 lb of coolant replaced about two weeks ago.

We do have a leak of some kind. It seemed to be running fine until yesterday when the coolant line iced up at the outside compressor. We let it defrost for almost 24 hours and turned it on again today. It's been on for about 2 hours with no more icing up, but the house hasn't cooled down much - maybe 2°.

We've noticed that one vent downstairs is putting out cooler air and with a stronger flow than all other vents.

The other vents are putting out just mildly cool air and you can barely feel it coming out of some of them.

We did also recently install smart thermostats (after the tech was here) and when the tech was here he found that one of the old thermostats wasn't installed correctly so the dampers weren't working.

Could the difference in air temp/force be the dampers again and due to changing the thermostats out (by amateurs)? Or are we probably low on refrigerant again? by Liz -

Reply by (mod) -

Liz

I'm sorry to say that if the refrigerant has leaked out in just a couple of weeks - as it sounds from your description - there is absolutely no point in adding more refrigerant - all that's doing is fouling the atmosphere and speeding the melting of the ice shelf in Antartica. Better will be to find and fix the leak before the next recharge.

If the A/C runs when the thermostat calls for cooling then the problem isn't the thermostats.

But before calling for repair again review the weak airflow items in the article above, as weak air flow can cause cooling coil icing.

Followup by Liz

thanks. The one thing we hadn't done was change the filters. They were obviously clogged.

The other thing we did yesterday was sawing through drywall so a lot of dust was kicked up. We'll see how well it cools now. I think airflow has already improved. As far as finding a leak vs replacing the system would you recommend finding the leak?

The system is only 10 years old and we've recently also replaced the blower fan (dirty air filters again, maybe we've learned that lesson).

Reply by (mod) -

Thank you for the update.
keep me posted

Followup by Liz - A/C Unit froze up again

Well, it froze up again. The tech just came and it's back down 2 lbs so we have a leak search appointment scheduled. Thanks for the info! This is a great site.

Reply by (mod) - find and fix the refrigerant leak

There can be several causes of the problem but the most common is low refrigerant, Liz, as we now all seem to agree.

Some techs may want to add a "stop-leak" product if they can't quickly find the leak.

That's an arguable fix as some experts warn that such products can gum up other controls or parts in the system such as the expansion valve that meters out refrigerant.

Find and fix the refrigerant leak. At this point anything else is throwing away money.

Weak air flow after fixing a coil icing problem

Hello there, I have a central air conditioner that froze up today.

The coils and the refrigerant line always freezes up when I set it to "cool"

I also noticed when I changed my filter that it seems there is no suction coming from the evaporator; however, the blower is working and I can feel (warm) air coming through the ducts/vents. Any ideas? by Larry from Guam USA

Reply by (mod)

Larry, please search InspectApedia for AIR CONDITIONER ICING to see the common causes and cures (often low refrigerant and a refrigerant leak) of the trouble you describe.

When ice blocks the cooling coil indeed the system won't be able to cool air passing through the ductwork.

Followup by Larry from Guam USA

Thank you so much for your reply... Even when the unit has been completely defrosted and I run the system on "on" (not cool) there seems to be no air being drawn into the coils but the blower is working and air is being passed through the vents. My concern is if the coil system is not pulling in any air on "on" mode, is this a problem?

Reply by (mod) - weak air flow after fixing a coil icing problem

Sure: you want to check the items in the AIR FLOW TOO WEAK including looking for a defective blower fan - loose belt or even just dirt on the fan blades - will drastically reduce air flow as will many other defects like an open, disconnected, or leaky duct system, improper blower motor voltage, dirty air filter, dirty cooling coil.

Either low air flow rate or low refrigerant can cause frost and ice blockage at the coil.

 

The fan blows very strong without A/C on, but it blows very weak when the A/C is on.

Hi,

The fan blows very strong without A/C on, but it blows very weak when the A/C is on. So, my house is not cool enough. Can you tell me the possible reason, please? Thanks. - by Anonymous

Reply by (mod)

I would check for low-voltage, a defective control on a multi-speed motor, or failing bearings, or if your blower is belt-driven I would check for a loose pulley or slipping belt.

You have already made sure that there's no blockage in the duct work, crimped or disconnected duct work, or a dirty air filter, right?

Trouble finding out why air flow is weak in our system: filters have to be changed every week!

We have to change the air filters about once a week. Our unit is fine and the drip line is down. Home inspector and several AC companies said it's fine but yet it's barely blowing inside.\

Once we even found water in the duct work. We sicked it out and checked for leaks. There are no leaks. We've even replaced sections of the duct work. Why is it still acting like it's blocked? by Serina

Reply by (mod)

First: it's VERY unusual to have to change air filters weekly. That suggests that there is an unusual dust or debris source in your A/C duct system, perhaps damaged fiberglass-lined HVAC ducts,.

If you still have the problem after finding and fixing that source of filter clogging then I'd ask:

Have you

1. had actual measurements of air flow at different points in the system or all of the consultants saying all is fine just expressing opinion based on no data?

2. has anyone checked for a dirty squirrel cage blower fan - dirt on the blades will substantially cut air flow

3. check for crimped, disconnected ducts or other defects listed in the article above.

Weak air conditioner air flow - is there a relationship between refrigerant charge level and weak cool air flow rate?

Les said: Weak air conditioner air flow: Our A/C was serviced two months ago and the repairman said it had a leak. $400 later it was recharged with coolant and now the ac is doing the same thing. Very little pressure coming out of vents and no cold air coming out. Does anyone know what I can do for the weekend? It is stifling!

(mod) said: no

Les: A leak that was fixed by a re-charge is not as good a repair as a leak that was fixed by finding and fixing the leak - you'll just have to keep adding refrigerant.

But weak air flow out of the vents would not be due to a refrigerant leak; more likely a clogged filter or crushed or disconnected ductwork, or a blower fan problem.

See A/C AIR DUCT PROBLEMS

 

Weak air Flow traced to Clogged Air Filters: Can Clogged Air Filters Affect the Room Thermostat?

If air conditioner filters are clogged will it cause the thermostat to shut off? - Jim

Reply:

Jim: clogged A/C filters won't cause a room thermostat to shut off. The thermostat responds to room temperature. However clogged A/C filters that reduce air flow, cause coil frosting, or otherwise reduce or stop the flow of cool air into the room where the thermostat is located would mean that the thermostat would remain "un-satisfied" and should mean that the thermostat says "on" - continuing to call for cooling.

See AIR FILTERS for HVAC SYSTEMS

Air Filters & Cooling System Amperage Draw: Could Removing the Air Filters Cause the Electric Motor in the Air Handler to Draw Higher Amps?

Question: got one for you. I put an ammeter on my air handler and it read 8.25 amps, I removed the filters and it went up to 9.75 lmao at the situation the amperage should have gone down.

What gives here - Lost

Reply: causes of variations in electric motor efficiency and current draw measured in amps

Lost: this amps variation is beyond my expertise, but in general reducing the load on an electric motor will show up as lower amps or current draw, not higher amps. Here are two interesting explanations of amps or current variations on an electric motor that I found when researching the question:

1. Voltage variations and current draw at electric motors:

If your supply voltage is varying from your power company that can show up as higher amps draw on the motor (though it's a suspicious coincidence to see it exactly when you removed the filters and supposedly reduced the load on the motor). Quoting from motorsanddrives [dot] com:

"The effect of low voltage on electric motors is pretty widely known and ... The amount of power the motor draws is roughly related to the voltage times current (amps). Thus, when voltage gets low, the current must get higher to provide the same ... To summarize the situation, low voltage can cause high currents"

2. Load variations and electric motor efficiency:

A second possible source of seeing higher amps or current draw on your blower motor when you pulled out the air filters and thus reduced the load on the blower motor might be illuminated by this U.S. DOE pamphlet "Determining Electric Motor Load and Efficiency" - Quoting:

"Most electric motors are designed to run at 50% to 100% of rated load. Maximum efficiency is usually near 75% of rated load. Thus, a 10-horsepower (hp) motor has an acceptable load range of 5 to 10 hp; peak efficiency is at 7.5 hp. A motor’s efficiency tends to decrease dramatically below about 50% load."

Effect on air flow if motorized air conditioning zone dampers not working

My house has "zone" control with dampeners to close off the upstairs over the garage room unless that thermostat is on - the room is not cooling. I have located the damper under the house. What are some causes for the damper not opening and how to repair them? condensation, motor to damper? silicon glued properly? - Becky

Reply by (mod)

Becky, If a motorized HVAC zone control damper is not opening or closing, most likely the motor has failed, or the thermostat that operates that zone control is off or set in an incorrect position.

See ZONE DAMPER CONTROLS

 

Question: why is there a gap under doors in my house?

I was trying to find credible proof as to why there is a gap under the doors all through the house. I've tried explaining return air for the H V A C and ventilation for the bath exhaust fan to draw air from. My wife wants to close the gap at the bottom of the bathroom door. Any advice? Tom Dalton

Reply: to improve air flow into rooms that have no return air inlet registers, just supply registers

Tom

In a house with central air returns, if you make the rooms more air tight by fitting tightly-closing doors you will certainly impede the delivery of heated or cooled air from the HVAC system - it's like trying to blow air into a balloon - you can do it, up to a point. Then your lungs just aren't up to the task. (Or you burst the balloon)