FAQs on repairing Indoor air handler or blower unit for A/C or heat pump or furnace systems, set #2:

More Q&A on AHU or air handler unit / blower unit troubleshooting and repairs.

This article series explains how to inspect & repair the indoor components of air conditioners and heat pumps: the air conditioning system indoor air handler units, blower units, or AHU's, (also called fan coil units) including the air conditioner blower fan, the indoor cooling coil or "evaporator coil", air conditioning system filters, and the causes, cures, and prevention of air handler leaks that lead to rust, damage, and mold contamination in the air conditioning system.

Air Handler / Blower Unit Diagnostic FAQs 4

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These questions & answers were posted originally

at AIR HANDLER / BLOWER UNITS - home - be sure to see the diagnostic help given there.

On 2020-01-26 by (mod) - ADP air handler won't turn back on

"then blows cold air" until switched off -
sounds as if the burner or heat source is going off (perhaps on high limit (safety)?)

On 2020-01-26 by john

I have an ADP air handler in attic. runs for about 8-15 hours ok. Than blows cold air and does not turn back on unless I shut it off at the circuit breaker and turn it back on. it has a zone control EMM-3 with 2 thermostats attached and zone relay bd in basement. . Checked blower, cleaned coils, replaced starter cap.

On 2020-01-02 by (mod) -

With the brand and model of your system you should be able to find at this website and download the manual that will contain a fault diagnostic table

On 2019-12-31 by Mark

We recently came across a fault in ahu unit. At the panel there was an indication of air fault and the fan runs for about 5 mins before tripping out. Motor is ok when tested and air flow switch ok just need some help for fault

On 2019-12-21 by Steve Dorcheus

Our home has a Goodman AC & Heating Unit (A42-15 208/240 VAC air handler/coil & outside unit is G8C130421AC) :

The blower starts within 30 seconds for heating, but takes about 5 minutes +/-for the blower to start for the AC after the outside unit has begun to run. The AC blower used to start with less time delay (less than 1 minute it seems).

What may cause such a lengthy time for AC handler/fan to start, while the heater start is timely? What is normal fan star timer delay for the AC and is there a permissive switch on motor start circuit?
A local repair tech wants to change out air handler, but argued with my question about possible issue with freon gas system as a possible cause. Would the freon circulation system have a pressure switch (permissive) in the circuit or some other control/relay that causes the slower AC fan start until gas condition is satisfied?. Please advise what you think is going on.

This delayed AC fan issue started last summer 2018.
So last summer, I left fan run continuously to frequent avoid motor starts & stops (fearing the air handler motor / motor starter circuit may be degrading), , and manually cycled the compressor (outside unit).

Cooled fine, but was a hassle waking-up to warm house and then manually running compressor for 15 minutes until house cooled again

It's winter now so not much need for AC to run, but there is a concern something is going on with fan motor start circuit.

Est replacement cost for air handler is $4,000 + wood work & sheetrock redress of enclosure, so we're a bit indecisive what makes most sense before we initiate a replacement. What kind of diagnostic can we ask tech to undertake to establish what is really going on and what remedy is needed.

The system is not very old and my gut feel is there is something about the freon circuit to be evaluated as much as AC motor starter/circuit.

The only parts replaced on system was an outside condenser fan and capacitor 2 yrs ago & freon checked. When the outside fan was replaced system was checked and given ok.

The entire outside condenser unit was replaced in 2010, but inside air handler unit was here when I bought the house. Probably less than 15 - 20 yrs old.

There was a freon leak in 2014 which was caused by outside unit installer in 2010 crimping smaller dia. pressure tubing, which finally began leaking. The tubing leak was repaired and system recharged at the time; System worked OK

Please advise.

Thanks and regards

Steve Dorcheus, Houston TX

On 2019-12-18 by Anonymous

replaced capcitor now air handler in attic won't turn on left unit out side run a while but Still no air coming thru the air handler any suggestions

On 2019-11-13 by (mod) -

Al:

Please find your question and a detailed reply including links to Rheem manuals that may help you out, now found at

BLOWER FAN SPEED SETTINGS

and help me out by asking whatever follow-up questions you need (on that page) and perhaps by posting a photo of your Rheem blower motor wire connector and wires

On 2019-11-13 by AL

Rheem air handler runs too slow when A.C. is on , but runs way fast when furnace is on. wiring must not be correct, am thinking I need to switch 2 wires , am I correct ? and which wires

On 2019-11-07 by Majer Joseph

soon I turn on my breaker the air handler on , with out turn on my thermostart and fan off

On 2019-10-11 by (mod) -

From your description it doesn't sound like it. Sometimes Tuesday foaming spray that rips into a pan for cleanup and may require less actions

On 2019-10-10 by james Quinn

I have a carrier air handler, attic mounted. I need to clean the coils. I cannot get to both sides. Can I access the coild without removing the duct work?

On 2019-09-14 by (mod) -

Roc

Rattles at the air handler unit can be as trivial as an inspection door not latched, loose hardware, loose duct connections, or as troublesome as a blower motor that's failing with bad bearings. You need to ask your service tech to take a closer look. Tell us what you're told by the tech and we may be able to comment further.

Also either search InspectApedia.com (using the search box just above OR in the ARTICLE INDEX just above see HVAC NOISE DESCRIPTIONS for a complete diagnostic procedure for just about every noise type.

On 2019-09-14 by Rocco

I have a brand new Lennox a.c. And handler installed. The handler located in the attic rattles why

On 2019-07-17 by (mod) - fan runs with control wires disconnected

That's crazy. We must be missing something. What the heck? Electromagnetic fields?

More likely we're wiggling something on a control, connector, or board;

On 2019-07-17 by Eric W

Dan, I’ll check what you said. The thing that is baffling is why it turns on when a length of wire is attached to just the red wire and the other end isn’t connected to anything. It’s not completing the circuit so it can’t be shorting out on anything and when that length is disconnected the fan won’t turn on.

On 2019-07-17 0 by (mod) - the fan comes on and will not shut off

Eric

Take a look at the debugging tips starting at FURNACE FAN WONT STOP https://inspectapedia.com/heat/Blower-Fan-Wont-Start.php

On a new installation I suspect shorted wires - just as you did.

When you disconnect the TT wires right at the air handler and the fan still insists on running then check for a FAN ON switch on the limit control (assuming this is heating & cooling air handler) and check any dip switches or jumpers on the fan control board.

On a new unit my last guess is a bad control board or fan relay.

On 2019-07-17 by Eric W

Installing a rheem air handler. Attached wiring for thermostat. Without connecting the other ends to the actual thermostat and turning the power on at the unit, the fan comes on and will not shut off. After thinking there was a short in the length of thermostat wire, so changed that, twice. Still comes on with the other end not attached to anything.

After playing around with it more, I took a length of single wire off a spool, attached it to the red wire in the air handler and nothing on the other end, disconnected the green and brown wire form the air handler, turned the power on to the air handler and the fan comes on.

If I take the length of wire off the red wire from the air handler and turn the power on, the fan does not turn on. It doesn’t make any sense....I even swapped out the circuit board to see if that was some how causing it, but it still did it. Does anyone have any ideas?

On 2019-06-14 by (mod) -

I wouldn't assume that the problem is a failed motor. It could certainly be a dirt, ice, defrost cycle problem, or bad control board or relay.

On 2019-06-13 by Steve

This air handler problem occurs even when only the fan is engaged

My A/C air handler switches on the shuts off, then switches on again. No pattern. I replaced capacitor...no change. All wires tight. Sometimes it runs for hours NP. Could this be the beginning of the need for a new motor or am I missing something?

On 2019-02-16 by (mod) -

Possibly the fan is mis-wired or a dip switch set incorrectly.

Also you'll see in the article problems with run direction related to a bad start/run capacitor.

On 2019-02-16 by Anonymous

It doesn’t run backwards but 1/4 turn then goes other direction and keeps doing that never spinning I did replace board with exact same one no different

On 2019-02-16 by (mod) - fan runs backwards - causes, effects

A fan that is reversing and running backwards can be caused by a power surge that damages a control board or relay or on occasion even the motor itself.

On systems that require cooling by a fan such as the outdoor condenser unit, a backwards-running fan will also permit overheating - the system may shut down on thermal overload.

On indoor air handlers a backwards running fan or a squirrel cage blower that's mounted backwards will mean weak air flow through the duct system.

More details are at ELECTRIC MOTOR RUN DIRECTION - backwards

https://inspectapedia.com/electric/Electric_Motor_Direction.php

On 2019-02-16 by Dave

Hi I have a Rheem air conditioner 2014 year. The air handler comes on and then immediately stops and goes back and forth each direction everything seems to be working except fan it does the same when put on just fan on any help would be appreciated

On 2018-11-30 by (mod) - heat coil turns on but not the blower

Watch The Fan limit control switch. If the temperature dial turns to the fan on position and the fan isn't turning on I suspect a bad switch or incorrect wiring.

On 2018-11-29 by Aaron

I have an air handler that the heat coil turns on but not the blower. If I turn on the ac the blower does work. What is my problem?

On 2018-11-27 by (mod) -

Josh,

It's really possible that the system could be damaged by repeatedly cycling up to the high limit and switching off. That can be caused by a dirty filter or lack of air flow through the system. A dirty blower could cause lack of airflow.

On 2018-11-27 by Josh

I had an HVAC tech come out an tell me trash had clogged up my blower motor causing the system to constantly switch off and on as well as burn out my motherboard. 1. Iit cost me 900, is this a fair price. 2. Is this even a possibility?

On 2018-11-30 by (mod) - blower does not turn on

Watch The Fan limit control switch. If the temperature dial turns to the fan on position and the fan isn't turning on I suspect a bad switch or incorrect wiring.

On 2018-11-29 by Aaron

I have an air handler that the heat coil turns on but not the blower. If I turn on the ac the blower does work. What is my problem?

On 2018-11-27 by (mod) -

Josh,

It's really possible that the system could be damaged by repeatedly cycling up to the high limit and switching off. That can be caused by a dirty filter or lack of air flow through the system. A dirty blower could cause lack of airflow.

On 2018-11-27 by Josh

I had an HVAC tech come out an tell me trash had clogged up my blower motor causing the system to constantly switch off and on as well as burn out my motherboard. 1. Iit cost me 900, is this a fair price. 2. Is this even a possibility?

On 2018-11-19 by (mod) - air handler blows circuit breaker

Most likely there's an overcurrent and the safe thing is to leave the equipment turned off until it is repaired.

We can't know exactly what's causing the overcurrent without more on-site inspection and diagnosis. From just your text I don't know if there's a backup heat issue a motor issue a control issue or a wiring issue

On 2018-11-18 by Anonymous

air handler blows circuit breaker

On 2018-11-14 by (mod) - if jumping the thermostat connectors right at the control board doesn't turn on the A/C

Dean if jumping the thermostat connectors right at the control board doesn't turn on the A/C nor heat pump and when you know that there is power to the unit I suspect

- a bad control board relay

- a bad control board

On 2018-11-14 by Dean

My outside unit will not come on in heat or ac I had the capacitor changed the defrost board changed I can push in the contacts and it comes on I have 24 ac to my tstat my fan in the attic comes on the heatstrips come on but no 24 volts to the contact to turn it on. My fuses are good the 3 amp fuse is good and I have 24 ac out of my transformer.

My wires are in good no breaks. I have a 3 year old goodman any answers deanclip@gmail.com.

On 2018-11-08 by (mod) - dirty sock smell or gym sock smell in air conditioning or heat pump systems

I have reviewed several Trane documents without finding reference to a new alloy - it would be most helpful if your dealer could point us both to an information source.

www.novellcustom.com/wp-content/uploads/2017/01/the-trane-difference.pdf - discusses using properly-selected metals to avoid corrosion problems, not odors

www.trane.com/Commercial/Uploads/Pdf/1028/coil-ts-2.pdf does not mention the word metal nor the word odor.

http://www.trane.com/WEBCACHE/AH/COILS%20(COIL)/SALES/COIL-SLB006-E4_01012014.PDF - discusses concerns with corrosion and vibration damage, does not mention odors.

Watch out: as I discussed earlier, some mold contaminants in HVAC systems, including in the ductwork, in the air handler, or on the cooling coil, can indeed produce unpleasant odors that include a variety of smells, some of which are described on occasion as "the smell of gym socks" or "the smell of dirty socks" - which in fact are mold odors.

Steps to reduce mold odors sometimes focus on trying to reduce mold growth in the system, using UV or using special coatings on the coil itself.

In my OPINION, while all of those steps are fine to take, they're band-aid approaches where what we want is to avoid mold growth in the HVAC system in the first place.

This problem was discussed in an industry publication: ACHR News on 13 March 2006

A New Solution Found for Dirty Sock Syndrome original source: ACHR News: https://www.achrnews.com/articles/97993-a-new-solution-found-for-dirty-sock-syndrome

A copy is also here: https://inspectapedia.com/aircond/Dirty-Sock-Odors-in-HVAC.pdf

Also see this paper on the effects of dirt in AHUs by Siegel

https://inspectapedia.com/aircond/Dirty-Air-Handler-Blower-Effects-Siegel.pdf

On 2018-11-07 by George - Trane has new alloy that resists air handler odors?

Thank you for your quick response - My units are Trane and the dealer claims that the metals are at fault for the smell during the change over period claiming they do not smell when completely wet or completely dry - says Trane has a new alloy for their indoor coils - can find nothing to substantiate this claim

On 2018-11-06 by (mod) - cleaning the blower unit

George,

What you are being told is consistent with my experience.

You would need to have the coils cleaned before turning on your air handler after a period of dis-use if you want to avoid the initial dusty odor and if you don't want the (costly) change-out to a dust resistant evaporator coil.

I'd also have the tech check the cleanliness of the squirrel cage blower fan itself. A small amount of dust on the blades can significantly reduce airflow, increasing system operating costs for both heating and cooling.

In addition, that dust, if it's normal house-dust, contains organic material including skin cells and some fabric fibers that, in the presence of moisture, can support mold growth that might also contribute to odors.

There are UV systems that can knock down biological materials on air handler surfaces that may also reduce odors but I don't recommend that in your case as you're complaining about what sounds like normal house dust odors.

If you can obtain the name of the dust-resistant coil products your tech has in mind I'd be glad to do further research.

FYI, experts like Siegel (2002) assert that dirt on coils makes a less than 10% reduction in air flow, while noting that "in extreme conditions" the effects may be much more significant.

In my nearly 50 years of inspecting air handlers and blowers and participating in the cleaning of some of them, I have seen an enormous change in air flow rates following cleaning.

That has been on the particularly-dirty blower assemblies. But on a 15 or 20 year old AHU blower fan it is very common to see the curvature of the individual blades filled to nearly-flat by dust and debris.

The fan spins at the same old RPM but its ability to move air is, IMO, and only subjectively-determined, very significant.

Here's a list of cleaning topics to review with your technician as steps to reduce odors from the air handler:

1. Clean the AC evaporator coil itself

2. Clean the blower fan and blower fan compartment

3. Replace the air filter monthly for each month that the system is in use in heating or cooling

4. Consider improved filtration such as an electrostatic air cleaner and, if the air speed and blower an handle it, HEPA filtration

5. UV treatment (which I'm not recommending for your case)

6. Also inspect for any mis-handling of condensate such as dirty condensate tray or blocked or slow condensate drain that can splash or spray condensate downstream in the air handler - inviting mold growth

7. Check that the AHU air speeds and system sizing are correct; an over-sized fan, for example, may keep blowing condensate off of the cooling coil and downstream into the duct system

8. Inspect to confirm there have been no other floods or leaks into the duct system

9 Inspect the home for other odor sources or mold reservoirs that might, by being close to the air returns, pick up and send odors or mold through the building. (Search this site for ODOR DIAGNOSIS for details).

Siegel, Jeffrey, Iain Walker, and Max Sherman. "Dirty air conditioners: Energy implications of coil fouling." American Council for an Energy-Efficient Economy 529 14th Street N.W., Suite 600 Washington, D.C. 20045-1000 Phone: (202) 507-4000, Residential Buildings: Technologies, Design, Performance Analysis, and Building Industry Trends - 1.287 (2002).
[PDF] retrieved 2018/11/06, original source: aceee.org/files/proceedings/2002/data/papers/SS02_Panel1_Paper23.pdf

You can also get a copy here: inspectapedia.com/aircond/Dirty-Air-Handler-Blower-Effects-Siegel.pdf

On 2018-11-06 by George

Air-Handler appears to be very clean - have professional maintenance twice a year and have 3" pleated filters - however, twice a year (spring and fall) the smell from the air-handler after using the heat and the next day requiring A/C smells like dust - very irritating - A/C company says it is a microscopic build up on the coils -

it goes away once we use either the Heating or Cooling on a consistent basis but is always there during the switch over weeks in Spring and Fall - what can be done to control this??? A/C company claims that they have new coil materials that stop this - but why pay for a coil change out - any thoughts???

On 2018-08-08 by (mod) -

See your question and our reply at BLOWER FAN CONTINUOUS OPERATION https://inspectapedia.com/aircond/Blower_Fan_Continuous_On.php#FAQ

On 2018-08-08 by Anonymous

I have a Carrier air handler ,on air conditioner side the thermostat is off but,the blower motor continues to run ?

On 2018-07-31 by (mod) -

Adding: if your unit had a power surge or lightning strike a motor may be running backwards.

On 2018-07-31 by (mod) - Compressor Startup or Rotation Error Diagnostic Flowchart - Samsung Error Codes E461 and E467

[Click to enlarge any image]

John,

Typically a "rotation error" pertains to an air conditioner compressor motor, and often the first diagnostic step is a power-on reset of the system.

But knowing not a shred of a microdot of information about your system, I am flying more blind than Mr. Magoo.

Start by looking at the compressor unit, note the brand name, then look at the data tag and note the model number and serial number. Then find the service manual for your specific model and there you will find a table of error codes and names as well as the recommended diagnosis and repair steps.

Or see MANUALS & PARTS GUIDES - HVAC https://inspectapedia.com/heat/HVAC_Manuals_Air_Conditioners_Boilers_Furnaces.php for help downloading the manual for your unit if you don't already have one.

Below is an EXAMPLE page diagnosing rotation error codes for certain Samsung split system AC models.

This flowchart helps diagnose Compressor Startup and Rotation Error Codes E461 and E467.

On 2018-07-31 by John

My fault code keeps coming up with a rotation error

On 2018-05-26 by (mod) -

Steve

Yes indeed, though it's a heck of a ride for the mouse.

Once the blower and air handler unit AHU have been cleaned and perhaps sanitized, I'd check the motor bearings. If the blower fan was off balance enough it could have damaged the bearings.

On 2018-05-26 by Steve

Is it possible for a mouse to get into the air handler and cause the fan motor to get off balance and stop working? Ours started making a loud noise and our ac tech says a mouse must have got in it and caused the fan to get off balance which caused the problem. I find it hard to believe that could happen.

On 2018-05-10 by (mod) -

The fuse for the circuit that power is low voltage Transformer that then Powers the thermostat will be in your electrical panel

On 2018-05-09 by Justin

Does anyone know where the 5 to 10 amp fuse is on a ease air by johnson air handler might be located for the 24 volt for the thermostat

On 2018-05-06 by (mod) -

Ok

On 2018-05-05 by Joe z

The evap motor does not come on with the thermostat fan on switch. It works on a call for cooling, compressor starts first, then ecm motor runs up to speed.

On 2018-01-16 by (mod) -

Bearing damage arises from failure to lubricate the bearings on schedule. You'll need to replace the blower assembly

On 2018-01-16 by Mahendra kumar

Again to again bearing damage what's is problem

On 2017-10-23 by (mod) -

Jan

See BLOWER FAN WONT START at inspectapedia.com/heat/Blower-Fan-Wont-Start.php

where we give diagnostic steps to check when the air handler blower won't run. Try that and let me know what questions remain.

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

Jan

at FAN, AIR HANDLER BLOWER UNIT inspectapedia.com/aircond/HVAC_Blower_Fan.php 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 see FURNACE FAN WONT START at https://inspectapedia.com/heat/Fan_Limit_Switch_Test_Procedure.php#FanNoStart

On 2017-10-23 19:09:50.014132 by Jan

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

...

Continue reading at BLOWER FAN OPERATION & TESTING - home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BLOWER FAN OPERATION & TESTING
  • BLOWER FAN CONTINUOUS OPERATION
  • BLOWER DOOR SAFETY SWITCH
  • FURNACE BLOWS COLD AIR
  • FURNACE FAN CYCLES AFTER HEAT
  • FURNACE FAN CYCLES DURING HEAT
  • FURNACE FAN STOPS EARLY
  • FURNACE FAN WONT START
  • FURNACE FAN WONT STOP
  • WOOD FURNACE FAN LIMIT CONTROL
  • CAD CELL RELAY SWITCH

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AIR HANDLER / BLOWER UNIT FAQs-4 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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