Photograph of attic air conditioning air handler, condensate drips on floor Air Handler Unit FAQs
Air Handler or Blower Assembly Q&A

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Q&A on the Indoor air handler or blower unit for A/C or heat pump or furnace systems:

This article series explains how to inspect & repair the indoor components of air conditioners and heat pumps.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Air Handling Unit / Blower Assembly Q&A

Photograph of toxic mold growth on a squirrel cage air conditioner blower fan unit[Click to enlarge any image]

Questions about fixing air handler units or blower units posted originally at AIR HANDLER / BLOWER UNITS - topic home. Be sure to check that article.

On 2017-10-23 19:58:38.314369 by (mod) -


at FAN, AIR HANDLER BLOWER UNIT we give diagnostic steps to check when the air handler blower won't run. Try that and let me know what questions remain.

If your air handle is for BOTH heating and cooling, then also


On 2017-10-23 1 by Jan - blower motor in A/C air handler won't turn on

The blower motor in ac air handler won't turn on

On 2017-09-28 by (mod) - air handler struggling when turns off


What you describe could be caused by any of a number of problems, more than I can accurately guess with so little information. Your service tech will probably consider a start capacitor for a motor that's having trouble starting or a bad controller relay

On 2017-09-28 by Dave

My air handler turns off but sounds as if it is struggling. The air flow isn't consistent. It is a Carrier installed in 2010.

On 2017-08-15 by Leaking water

The air handler is in the attic and is dripping water on top of the ceiling of house. My problem is trying to find the drip. Any suggestion where to look? I cannot find the drip.

On 2017-07-01 14:18:09.521072 by Kenneth Wood

Very great information thanks

On 2017-06-22 03:46:39.369964 by (mod) -

Perhaps a faulty door safety Interlock swirch

On 2017-06-21 08:14:45.967510 by Vusi

What cause a fresh air unit aircon to cut off when the doors are closed but switches on again when the door is wide open but after sometime it overheats.this is very confusing because there are no limit switches or sensors on the doors becauce i would suspecr maybe they might be faulty

On 2017-06-05 03:40:20.460368 by (mod) -

There are several possible problems but I think a good place for you to start with b at this diagnostic article

On 2017-06-05 00:24:30.893291 by Rick

I have a Rheem RHSLHM3017JA The indoor fan motor will not stay on. Replaced fan motor and T Stat.

On 2017-05-19 01:59:47.753248 by (mod) -

That sounds like a failed control or shorting wires.

On 2017-05-18 16:54:19.181238 by Andrew Biello

My air handler fan goes on and off even when the unit is off. system works fine but when temp reaches setting on thermostat unit will turn off then fan will go on and off every couple of seconds. Only way to stop is shut breaker to handler.. Very strange.

On 2017-05-15 by (mod) - Guides for evaluating HVAC System Performance and Functionality


it's a perfectly-good question but not one I can answer. I think that if an A/C takes many hours to reach the set temperature in a building then on a still-hotter day it simply won't get there at all. But the problem might not be the equipment itself.

It could be undersized, have leaky ducts, be in a building that's not insulated, exposed to unusual solar gain, etc. So someone onsite needs to see what's going on.

More often HVAC guys talk about how long it takes the A/C system to drop the indoor temperature by 2 degrees: that avoids the capacity but not the open-window problem.

Rules of thumb for A/C performance:

Typically, in a properly-sized residential A/C system, assuming no stupid conditions like someone left the windows open, in 20 minutes a small room should be noticeably cooler, and in 3-4 hours the system should be able to drop the indoor temperature by about 10 degrees F.

More technical approach to AC cooling performance:

There are performance standards for A/C and heat pump systems. Typically those specify a given set of test conditions like:

Operating Condition A: 95°F outdoor air temperature, 80°F dry bulb/67°F wet bulb indoor coil air entering conditions. [Energy Star]

A useful standard is "ANSI/AHRI Standard 210/240 with Addenda 1 and 2 (formerly ARI Standard 210/240)" describing a four-hour test cycle.

Hou has written a theoretical paper on this that, if you can stand it, gives insight to why a simple answer like " it should take no more than 2 hours to cool down your room" are difficult:

This guide is focused on indoor air quality and what measurements are made such as of air velocity, % of fresh air, etc. - we don't get help with "how long should it take to cool my room"

On 2017-05-15 by Ken Stocke - How much time does the AC system have to reach a degree below setting to be performing acceptable.

How much time does the AC system have to reach a degree below setting to be performing acceptable.

On 2017-05-08 by (mod) - air blower won't shut off


I used the InspectApedia search box above to search for "fan won't stop running" to find this diagnostic and repair article


that suggests what you should do

On 2017-05-08 by patrick

air blower won't shut off

On 2017-03-06 by (mod) - as soon as unit is switched on the coil gets very heated

Is this a heat pump?
Are controls working properly?
Is it in heating mode?
Is there an auto-defrost cycle running?

On 2017-03-06 by Anmol

My ahu cooling coil is chilled when units if switched off. But as soon as unit is switched on the coil gets very heated.

On 2017-02-25 20:22:46.189169 by John

Why actuator do not let heat when needed

On 2017-01-27 19:40:13.884811 by Adam

Older Westinghouse air handler keeps blowing internal fuses--why?

On 2017-01-27 19:39:30.063684 by Adam

I have a Westinghouse air handler (circa 1979) that continues to blow internal fuses, trying to determine what to test and replace. Model # AJ010CRW, Style 3976A62G01

On 2016-12-19 15:44:31.507253 by Anonymous

I just installer a air handler with heat strips and my fan relay keeps clicking and no fan

On 2016-12-15 02:15:40.447301 by Ben brown

I have a goodman unit. Outside unit and air handler in atic. Replaced defrost board and compasiter on outside unit. Also replaced the fuse in the air handler and still not working outside ?. Any ideas

On 2016-11-18 21:01:06.671488 by police luutenent needs me iwas living qith werewolves and i brought my children to berkeley

his son attempt to be near someone while these two were to get her would lead to this policefollowi g him for
Quinn haber and his father whoso much time asking stores to accuse him of taking things for jeep resident California fresh market

then removing his own sin and telling g nation. that he is the son. this. group attorneys claim to give suit against police were William morris attorney after eating his almond Roca ask Dave to tell people he walked up to Quinn haber and William haber

police telling g the planet they followed him since 16

allowed the father to be the son

being harassed by white people that try to put them selves or rather their disease in his body. by. hanging out near him.

he feels good and paid police to allow the to use body to feel better

leading to obvious job and sexual harassment from govt and state city county employees wanting to be apart of William Wantedtoeayi I am reallyyourfriendandbeleivingeisnerfrienfshipmeans
His family and life
Ask police if they could give him homopapioma

That his father help eisnerfriends. Ask why is your community helping h I'm he is my son
We ask that Susan romig speak to his wife's ex husbandAsking that he remove the son from his wife his motherThis attempt yo stop his job police attempt to tell us they care and will make sure people beat him up for the parents His original attempt to see ovitz son at William morris care for poor person is police joke. Eisner and police help steal his things to give to the father. Chinese and residents of California. A FBI joke asking Arizona to make a homeless person so they can end his life Troubled cause he can't find proper attorney with out this William haber money. These that are his family give their money to police supporting removing him from his parents for this William morris way of thinkingWhy would you hang out with usSo this final attempt to form psychological workers to ssask first that inventory stop wanting to through things at him but rather prison for Poor wwe can't like so his parents sdont have to here he is alive

On 2016-09-15 18:55:34.986488 by (mod) -


If your unit is a heat pump look for backup heat that is ON when it should be OFF - typically a control board relay problem, sometimes shorted thermostat wires.

On 2016-09-15 18:22:49.390426 by Tom

My heat is blowing when the air conditioner is supposed to be on all of a sudden. What do I need to do?

On 2016-08-12 22:24:08.334878 by (mod) -

RE: WHICH WAY does the AIR FILTER GO regarding its ARROW?

Dave we've got several articles on air filters including location and placement beginning at See AIR FILTERS for HVAC SYSTEMS (search InspectApedia for that phrase).

In general the ARROW you see on the edge of the filter should point in the SAME DIRECTION as the AIR FLOW in the air handler.

Take a look inside your air handler.

You'll see a big opening that brings IN air TO the air handler FROM the RETURN DUCT.

You'll see another big opening that sends air PUSHED by the BLOWER IN to the body of the air handler or TOWARDS the COOLING COIL.

So air is moving FROM the RETURN DUCT - TOWARDS the COOLING COIL inside the air handler.

Whether that is up or down, left or right, depends on the design of the particular air handler - and of course I can't see yours.

Let me know if this works for you or else ask again.

On 2016-08-12 14:46:04.069534 by Dave

I'm a little confuse about which way to insert the filter in my central AC air handler?
I have a vertical air handler in my basement that supplies air to the whole house, is the filter arrow pointing toward the floor the bottom of the air handler in the direction of the condenser outside the house or up toward the ceiling and the evaporators?
I've read that the arrow needs to point toward the Blower Motor, is the Blower Motor above the coils toward the ceiling or under the point where the filter goes in? I think there is nothing under the filter opening on the floor of the air handler.
Thanks in advance

On 2016-07-23 16:53:40.216161 by (mod) -

Dick I'd look for a bad thermostat, thermostat wire, or blower unit control board or relay.

On 2016-07-23 00:11:45.588540 by dick

I have an old Goodman air handler. Often the compressor starts and the air handler blower does not and I get a freeze up. Our current solution is to leave the blower motor running all the time. What is causing this? I have heard it is the relay board and have heard it is just a relay. Any answer will be appreciated.


On 2016-07-18 18:27:38.483810 by (mod) -

Yes, Rose.

On 2016-07-18 10:41:21.045065 by

My air is on but bUT barely can feel cold air at vents could it be my filter?+

On 2016-07-05 16:45:41.429394 by (mod) -

Brad please search InspectApedia for THERMOSTAT WIRING to see a sickening number of articles on wiring thermostats by brand and type. Bottom line: it will help to know the thermostat brand and model and then to check the wiring diagram in the installation manual.

Having a thermostat that permits more wires than you need is rarely a problem: typically the 5-wire TT is simply providing hookups for more features than your older system (and thermostat) used. The un-used features and connections are usually ignored.

I'm not sure what relays you ask about - heating + cooling? Relays are in the air handler and in the compressor/condenser of an air conditioner or heat pump. Mulitple.

On 2016-07-05 08:54:15.817628 by Brad

I got a new thermostat for free from a friend that does heat and air. But I have to have a 5 wire thermostat wire. My thermostat wire in only a 4 wire. Is there any advantage of having the 5 wire thermostat vs. the 4 wire other than it doesn't need batteries?

At least I will be able to eliminate one of thw possible problems and it not cost me anything.

Just my time pullling a new thermostat wire and mounting the new one. Thank you for your help danjoefriedman. I will let you know if thia fixes the problem. BTW do most residential system have one or two relays?

Or do they usually only have one relay for both the heating and cooling? I have no idea if mine has one or two. If it has two I might be replacing a relay too.

On 2016-07-04 16:54:40.354152 by (mod) -

Intermittents are hard to track down unless by luck the problem occurs when the tech is on-site. Often we find a loose wire, bad switch, bad relay. To me this sounds like a control board problem.

On 2016-07-04 05:55:00.053197 by Brad

I have an intermittent air handler fan problem. Sometimes the outside compressor unit will come on and the inside fan will not start.

It usually take 10-15 seconds. Of course if not caught soon this causes the coils and compressor to freeze up. I can immediate turn off the the cooling mode and put it in heat mode, run the thermostat set point up, heat unit kicks on at the thermostat and about 15-20 seconds later the fan comes on just like normal.

So why will the inside fan come on when in heat mode but intermittently doesn't come on in AC mode.

Alot of times after switching the thermostat from AC to heat, run the system til the inside fan comes on in heat mode, then switch it back to AC mode the inside fan will come on.

After that the AC system will run fine for a couple days or on the very next cycle on the inside fan will not cone on again.

Personally I am starting to think it might be the thermostat that is bad. Since the inside fan is coming on everytime and all winter it works fine. It only doesn't come on sometimes in the AC mode. Any help would be great.

On 2016-06-01 10:17:06.560325 by (mod) -

Check the blower door safety switch too

On 2016-05-31 21:26:21.227968 by Ken Neyhart

The outside unit is running but the air handler is not, I have checked all of the obvious things such as the breakers over flow switch etc. Pan is dry. This unit is only 4 years old.

On 2016-05-02 15:17:06.244864 by Anonymous

Our brand new sanctuary in our brand new church is hearing a very loud (annoying) squeak (screech sound) when the air conditioning first comes on.

It is a metal building and the duct work is visible. The system works fine once the air flow gets going but the screech when it first comes on (especially during communion) is really annoying. Any thoughts on what could be the problem?

On 2016-04-12 13:08:26.870625 by (mod) -

Sorry I don't understand what " suction is not working properly" to which you refer means.

If your HVAC system is "running" but not delivering air, then there is a problem with the duct system or air handler that needs to be found and corrected.

On 2016-04-12 12:53:26.549129 by suncity medicare

if suction is not working properly, is that possible that we can use the high speed fan in ducting which is connected to AHU, We are not receiving cold air in our modular operation theater .

On 2015-11-19 20:30:03.646607 by (mod) -


The dryer vent idea sounds backwards to me and perhaps not approved by your water heater manufacturer: that is, normally the dryer vent mounted on an exterior wall includes a flapper that opens when the dryer is blowing OUT to vent outside; when the dryer stops the flapper closes by gravity - keeping birds and rodents and drafts out.

You wouldn't rely on such a vent to add combustion air as it'd not admit air when needed. If you install the vent backwards or on the inside of the wall you invite birds or rodents to enter the utility area.

A screened opening or perhaps a draft inducer fan that turns on to bring air into the utility area when the heater operates could work for some heating systems but a gas water heater won't on its own provide the necessary control.

Ask your inspector for more specifics and send that information to us by using our page bottom CONTACT link.

Ask your Rheem supplier or Rheem's technical support for what they'd approve. Call Rheem tech support at 1-800-432-8373

On 2015-11-19 19:05:25.790579 by Mark

I had my new Rheem 50gal Natural gas Hot water heater inspected for my permit and failed. According to new ordinances, i do not have enough ambient air volume in the room now? Choices, a $400.00 Vented door,

or, the inspector said they sell units that look like dryer vents for $50 $60 dollar that I could install to let more air from outside come into the basement area, they have a one-way flap so no heat escapes. Fine, but I don't know what this is called and I cannot find anything like this online?

Can anyone tell me what I need? he also stated I need a filter now for the gas line coming into the hot water heater too?

Anyone know what that is called as well, so I can get these items? Thanks in advance for nay help!

On 2015-10-08 14:11:56.221604 by Bobbi

when turned on it blows heat for maybe 3-4 minute maybe , then it just runs blowing out cold air . the air condtioner on it works fine .

I am at a loss at what is causing it not to put out any heat , I know diddly about heating and air cond

On 2015-07-30 17:19:32.332243 by (mod) -

Am, George and other readers, please Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies,

On 2015-07-30 14:35:45.904620 by (mod) -


Look for flexing ductwork or for a loose blower or component in the air handler.

Question: air handler not running

(Feb 5, 2014) GENE said:

My air handler unit won't come on



See AIR CONDITIONER WON'T START How to Diagnose & Repair an Air Conditioner that Won't Start

for help with the problem you cite - IF you are talking about a cooling system or heat pump

If you are asking about a heating system or if the heater runs but the blower won't start,


for diagnosis and repair help.

Question: air handler control board fuses blown

(May 18, 2014) Gary Matthias said:

Blown fuses (3A) on the air handler control board? Carrier Model CD3BXA036000AAAA made in 1995 repeatedly blows the fuse on the control board. I replaced the thermostat, disconnected one of the wires to the blower motor, but still have the problem.

The Red LED light on the board begins to flash after the fuse has blown. Any suggestions would be appreciated, I have limited electrical knowledge, but I do have a voltage meter and can generally troubleshoot or component replace. Thanks


Blown fuses on a control board often take you to a faulty control or control board itself; check the obvious: loose or damaged wires; hard-starting motors, burnt relays, contacts.

Question: loud thumping sound after the a.c. turns off

(July 24, 2014) H.Mulligan said:

My blower unit makes a loud thumping sound after the a.c. turns off. It sounds like something hitting against something. It sounds like air on a fan. Fan unitbwasvreplaced last year. Technicians can't find the problem.



Did you check for loose fan, bad fan bearing, or motor mounts that jiggle as the spinning components in the air handler slow down?

Question: buzzing noise coming from the Return Air Handler

(Sept 16, 2014) barbara holton said:

there is a buzzing noise coming from the Return Air Handler. I live in an apartment and they keep putting screws on the metal plate and the noise stops but then the buzzing returns later. If I switch the unit off at the circuit breaker the noise stops. Do you think it may be the transformer or relay switch. Thank you



You're doing a better diagnostic job than your repair people. I agree that one should look for the buzzing component: often a failing low voltage transformer or a control relay.

Take a look at LOW VOLTAGE TRANSFORMER TEST for details.

Of course other vibration noises might be tracked to loose duct components or blower components, even an access panel. Those noises would also stop when the equipment is shut off.

Question: strong air flow buckled air handler door - makes noises

(Sept 26, 2014) Don Brown said:

Had a new ac unit installed and have great air flow that causes the air handler door to buckle and retract when blower starts and stops making an annoying sound. Any suggestions?


Don it sounds as if there is inadequate return air ducting - the air handler is air-starved. I'd look into that problem rather than just stiffening the door. Just improving the door to stop the noise is treating the symptom not the problem.

Question: The heating coil has ruptured

(Oct 1, 2014) Jimbo 10/1/14 said:

I have a small air handler with both cooling and heating coils inside. They are very close to one another and the air must pass over both of them regardless of whether heating or cooling. The heating coil has ruptured twice in a three year period.

I am being told that this will happen if the air conditioner is running and the heating coils have cold water in them.

I guess I am being told that the water in the heating coil is freezing and expanding. This does not make sense to me. Must I drain the water out of the heating coils at the end of each heating season?


(Oct 5, 2014) (mod) said:

I'm with you Jimbo - I can't make sense out of what you're being told. I don't know what sort of equipment you've got installed.

Question: how long does it take for mold to grow on the air-conditioning unit?

(Oct 18, 2014) Donielle said:

How long does it take for mold to grow on the air-conditioning unit?



When conditions of moisture and temperature are favorable for molds commonly found in buildings and mechanical systems mold can grow in 24-48 hours.

Question: air handler door safety switch voltage

1 Nov 2014 Anonymous said:

on the air handler door safety switch , would like to know what volts is suppling the switch and where thanks.

Reply: proper blower door safety switch voltage, installation, replacement, repair


Usually a furnace or air handler blower door safety switch carries 120 volts. The switch is connected in series between a relay in the air handler that operates the blower fan and a terminal on a control circuit board in the unit. The switch is not powered independently. It's power comes through the circuit board.

You'll be able to see this by following wires from the blower door safety switch back into the air handler.

WATCH OUT for dangerous shock hazards. Be sure all power to equipment is off before touching any switches, wiring, etc.

Replacement blower door switches are easily obtained for your air handler by brand and model via your local HVAC supplier, from the manufacturer, or often online. Some safety switches will work properly on several air handler brands and models.

I add that the blower door switch is an important safety feature that helps avoid chock or chopped-off fingers or worse. Be sure that your replacement switch is properly mounted so as to be reliably operated by the blower compartment door(s) - the switch opens- cuts off power - when the door is opened, and is depressed in to close and permit power to the blower when the door is properly closed.


Question: blower door switch voltage

(Nov 2, 2014) Anonymous said:
On the air handler door safety switch , would like to know what volts is suppling the switch and where thanks.



Usually a furnace or air handler blower door safety switch carries 120 volts.

The switch is connected in series between a relay in the air handler that operates the blower fan and a terminal on a control circuit board in the unit. The switch is not powered independently. It's power comes through the circuit board.

You'll be able to see this by following wires from the blower door safety switch back into the air handler.

WATCH OUT for dangerous shock hazards. Be sure all power to equipment is off before touching any switches, wiring, etc.

Replacement blower door switches are easily obtained for your air handler by brand and model via your local HVAC supplier, from the manufacturer, or often online. Some safety switches will work properly on several air handler brands and models.

I add that the blower door switch is an important safety feature that helps avoid chock or chopped-off fingers or worse. Be sure that your replacement switch is properly mounted so as to be reliably operated by the blower compartment door(s) - the switch opens- cuts off power - when the door is opened, and is depressed in to close and permit power to the blower when the door is properly closed.

Question: clearance distances around air handler and heat pump

(Jan 16, 2015) Anonymous said:
I have heat pump and the air handler is in the basement what is the distance from the back of the air handler can we build a wall



Take a look at the installation specifications for the air handler and heat pump you installed - you'll see that the manufacturer gives allowable clearance distances both for air circulation and for access to perform various maintenance and repair tasks. Some equipment back sides, if there are no openings or no removable panels on that side, may be permitted just inches from a wall - it depends.

Or tell us the brand and model of your unit and we can help look for the specifications.

Question: trouble cleaning the squirrel cage blower fan assembly

Feb 10, 2015) KARL BALDWIN said:
I have a squirrel cage fan cleaning problem. The fan is in a Mitsubishi, Mr. Slim MSZ-A15NA indoor unit. The squirrel cage fan can not be removed for cleaning due to problems with the installation location. Twice a year, the fan blades get caked with dirt, reducing airflow.

To clean it, I 1st have to place a large plastic sheet below the unit to catch all the drippings. I then use Frost King Foaming Cleaner, which I spray directly onto the fan blades, from the bottom of the discharge vent as I manually rotate the fan.

After letting it soak, I then flush the cleaner and dirt out with a pump spray bottle filled with vinegar. I usually have to repeat this messy endeavor 2 or 3 times to remove the majority of the dirt build-up.

While the above procedure gets the job (partially) done enough to restore airflow, I'm trying to find an alternative spray cleaner that would do a better job. Mitsubishi engineers had no suggestions other than to point out that the build-up comes from pollution within my house.

But other than humidity, there is little else that I know of to cause the build-ups as I also have supplemental filtration - Filtreat Foam covering the air intake ducts on the unit and a pair of German made, VENTA Air Wash units placed on the floor.

My question, other than asking if you know of an alternative spray cleaner that would do a better job, is if you can offer any other better solutions. Thank you for your time.

Karl Baldwin



I think you are using the right cleaner and I agree that it is a lot of work and a mess.

And I agree that even a small amount of debris on the blades of a squirrel cage fan can significantly cut airflow - I've measured CFM rates before and after cleaning.

In my opinion you should not have to clean the fan very often, certainly not annually.

I would look carefully at these sources of crud that can clog a blower fan.

- leaks in the return duct system that pick up crud from somewhere enroute

- missing, improperly fitted and leaky, or poor filtration level at the return air inlet filter

- damaged fiberglass insulation inside the ductwork

- debris generators in the air handler such as a fraying belt on a blower assembly or oil or grease leaks nearby

- leaks into the air handler return plenum or blower compartment

If the problem were an unusual source of particulate debris in your building itself, we ought to be able to see that right on the air filter.

There is a chance that a lab analysis of the air filter contents might point to an unusual particle source.

Use our email at the CONTACT link at page bottom if you want to arrange a pro-bono forensic lab examination of a dust sample from your blower fan blades and/or the filter following the procedure I document at

Question: sealing air handler leaks

(Feb 20, 2015) Valerie said:
If a air handler is installed in the attic, should the unit be sealed so it doesn't suck in dust particles from attic insulation? Should an HVAC company inspect attic blown in insulation if the house was built before 1975?



as long as there is adequate return air being taken from the occupied space of the home, the air handler ought not be pulling dust from the attic. Ask your HVAC techs to confirm that return air is adequate .

You can also inspect the air handler interior for presence of attic insulation dust.

But yes I'd use foil tape to seal any leaks.

Question: economical to replace air handler parts or not?

Anonymous said:
Is it worth replacing the metering device coil of the air handler vs replacing



That depends on the equipment age and condition. It may be economical to do so. What does your HVAC service tech say?

Question: heat pump is running but not cooling

(July 2, 2015) Anonymous said:
heat pump is running but not cooling


Check out the DIAGNOSTIC GUIDES A/C / HEAT PUMP link found at Continue reading where you will find an INDEX to RELATED ARTICLES.

Question: water dripping from air conditioner supply registers

(July 10, 2015) Bill Coots said:
Our central air system has begun dripping water at the individual room vents. Is this a sign of pulling warm attic air into the evaporator/blower assembly and then condensing this warm air as it is being returned to the rooms of the house?


Bill without onsite investigation we can't know for sure why water is dripping out of your room vents when the AC is run. The problem could be return air duct leaks, missing insluation, leaks into the ductwork, condensate mis-handling (if condensate can leak into nearby supply ducts), or condensate blowing into the ductwork out of the air handler because of a condensate capture and disposal problem there.

I'd take a look in the attic, first for obvious duct leaks or disconnections, and second at the condensate handling system. Map the dripping supply vents to the attic duct locations to see where to look closely.

Question: AC unit in attic does not shut off

(July 16, 2015) Jodi said:
When my outside unit shuts off the attic unit continues to run and will not shut off, even after turning the whole system off the fan on the air handler unit in the attic continues to run, any ideas what this could be?



When you are "turning the whole system off" and the air handler fan continues to run then we think that either there is an electrical wiring or a control board or relay error (you'd need an electrician) or you are not finding all of the shut-off switches. For example turning off power to the outside compressor/condenser unit does not turn off power to the indoor air handler unit.

In other words, if you actually turn off electrical power to the unit, for sure it has to stop running or there is a wiring or switch error. In that case switch off the circuit breaker.

Some fan controls include an always-on switch as do some thermostats. Check for those.

(July 16, 2015) Jodi said:
Thanks for your input but it was a bad relay switch

Question: OK to run the blower if blades are missing from the squirrel cage fan?

29 Jul 2015 Am said:
Is it possible to run a squirrel cage blower fan with some missing blades without damaging the motor? Have a portable ac with a plastic blower fan. Removed a couple broken blades. Fan turns freely. Thanks for your advice!

Reply: no


I am doubtful. The problem, if there is one, is not so much reduced air output as that if the fan is out of balance it may destroy the fan bearings. Possibly you'll know that a balance problem is occurring by hearing or seeing vibration or wobbling when the fan runs.

Personally, I'd give it a try if it were my unit, but I cannot advise the public to do the crazy stuff I might try.

Am said:
Thanks danjoe. I did try it, what the heck much easier. But sound let me know it was horrendously imbalanced right quick. Oh well.

Reply: AM well at least we know the score. It's time to leave the machine off until the part is replaced.

Question: thumping brick falling noise when AC shuts off on the roof unit

George said:
When AC roof mount shuts off there is a noise like a brick is being dropped on the roof.
Is this normal?
Had a barometric damper on previous house that did not make noise.



Look for flexing ductwork or for a loose blower or component in the air handler.

If the noise is coming from a relay, compressor motor, fan motor, or other electrical component, shut off the system while waiting for repair.


Continue reading at AIR HANDLER / BLOWER UNITS - home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AIR HANDLER / BLOWER UNIT FAQs-2 - more-recent questions and answers about air handler units AHUs Blower Units Fan Units

Or see AIR FLOW TOO WEAK diagnose weak air flow

Or see AIR HANDLER BLOWER DOORS - how to find and open the blower compartment door or cover



HVAC Blower Fan Articles

Suggested citation for this web page

AIR HANDLER / BLOWER UNIT FAQS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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


Ask a Question or Search InspectApedia

Questions & answers or comments about how to diagnose & repair problems with the air handler or blower unit / fan assembly in a warm air furnace or air conditioning system .

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.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher - Daniel Friedman