AHU Air Handler Unit Indoor blower fan troubleshooting diagnosis & repair.

This article series describes in detail the testing and diagnosis of problems with air conditioning fans and with forced warm air heating blower fans found in the indoor blower or air handler or AHU.

When the blower fan won't start the problem could be something as simple as a blower compartment door that is not fully closed, or a clogged condensate drain.

How to Diagnose & Fix a Blower Fan that Will Not Start

Why won't my furnace blower fan start on its own? It will run if I give it a "spin"

My gas heater isn't working correctly. My thermostat signals the heater correctly and the burner ignites, but the fan doesn't always turn on.

If I open the panel and spin the squirrel cage a little, it immediately begins to blow air and runs the heating cycle. What could this be? - Mike.

Photo: an electric motor using a pulley and belt to drive the fan in an air handler.

[Click to enlarge any image]

Reply: Check or replace the blower fan motor start/run capacitor

Mike:

Often when an HVAC fan won't start on its own but will start and keep spinning when you give it a push that means that the start-capacitor for the unit has failed.

It's an inexpensive part that can be installed or replaced by your HVAC service tech or by a homeowner who has expertise in electrical wiring, using a VOM, and following simple wiring instructions.

12 Reasons that an Air Handler, A/C or Furnace Blower Fan Does Not Run

Photo: a direct-drive air handler blower motor on a nicely-cleaned AHU.

Before we focus on the motor and controls of the air handler blower fan (used in both air conditioning and heating systems) let's ask if the trouble is not specifically the blower fan but more basically: the air conditioner or heater itself just won't start in response to a call for cooling or heating.

To rule out trouble outside of the fan or air handler itself, check:

• A/C won't start or lost cooling capacity: If your air conditioning or heat pump system has lost its cooling capacity or won't start at all
  
  see REPAIR GUIDE for AIR CONDITIONERS. Make sure that all electrical power switches for the system are "on" and that the thermostat is properly set.
• Heat won't start or lost capacity: if your heating system or heat pump (warm air heat) won't start at all,
  
  see HEATING LOSS DIAGNOSIS-FURNACES.

Now we can continue by assuming you're convinced the trouble is right in the air handler. So take a look at these most-common causes of failure of the AHU blower fan to run. I've arranged this list roughly in order of probability and also in order putting the easiest and simplest things to check first.

Most homeowners can check the first six of these things by simple observation.

Watch out: turn off the electrical power before opening and inspecting the interior of the air handler or its blower compartment. There are risks of chopped off fingers or even death by electrocution if the equipment is not completely turned off.

Certainly most homeowners (except my mom) can check to see that the thermostat is set to call for heating or cooling, and you can look to see if a blower compartment door is open or the condensate tray is full of water.

But for electrical inspection and testing of components or switches, if you are not trained, comfortable and confident with using basic electrical test tools like a neon tester or VOM or DMM to check for electrical power, do not try it and don't touch anything. Instead call your HVAC service company for help.

1. Controls are not calling for heating or cooling
   
   - a thermostat or sometimes electronic control board fault
   
   See FAN AUTO ON THERMOSTAT SWITCH
2. No electrical power to the fan or its controls
   
   - check for a blown fuse or heating or cooling switch set to off.
   
   Check for a loose or disconnected wire or a corroded electrical connector.
3. Open blower compartment door
   
   - a safety switch may be preventing fan operation -
   
   see BLOWER DOOR SAFETY SWITCH
4. Flooded condensate drain tray
   
   - for heat pumps and air conditioning systems that use a sensor switch to detect water in the condensate overflow pan, this condition can prevent the air handler from running in air conditioning and heat pump systems -
   
   CONDENSATE PAN SWITCH LOCKOUT
5. Loose or broken fan belt
   
   On belt-driven blower assemblies - the blower fan motor runs but the fan does not turn
6. Loose pulley
   
   on belt driven blower assemblies - the blower fan motor runs but the fan does not turn
7. Damaged blower assembly shaft or bearings
   
   - a seized fan assembly (unusual). The motor will draw abnormally high amps.
8. Bad fan motor start/run capacitor
   
   - See details
   
   at FAN MOTOR START CAPACITORS
9. Bad fan control relay
   
   in air conditioners or air handlers that use a control board or relay to operate the fan the relay or other control board components may have failed.
10. Bad fan limit control switch
    
    in heating furnaces -
    
    see FAN LIMIT SWITCH TROUBLESHOOTING
11. Overheated electric motor,
    
    off on thermal reset -
    
    see MOTOR OVERLOAD RESET SWITCH
12. Bad electric motor
    
    for the fan or blower itself -
    
    see ELECTRIC MOTOR DIAGNOSTIC GUIDE

 

 

Reader Q&A on Blower Fans

Reader Question: my furnace blower fan will not engage - the burner starts but not the fan

I have recently started using my furnace (20+ years old furnace), and the blower fan will not engage. The pilot and gas burners start, but the fan does not. I have ensured that the fan is set to "auto", on the thermostat. Is there any procedure I can do to troubleshoot the issue? I have seen several topics, however none seem to be helpful. - J.B. 12/31/2013

Reply:

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. But here are some suggestions to start troubleshooting the problem of a furnace blower fan that does not start:

Step 1: I would start by confirming that the blower fan will operate. Your system probably has a manual FAN ON switch on the thermostat, or if not, there may be a FAN ON push pull switch right on the fan limit switch in the air handler.

If you can make the blower run then we know the problem is not with the blower motor or drive belt or assembly and we'd go to step two.

See  FAN AUTO ON THERMOSTAT SWITCH for the switches on the thermostat;

For a manual FAN ON switch found on some limit switches in the blower or air handler assembly itself

see CONTINUOUS BLOWER FAN OPERATION

Step 2: I would continue diagnosis by watching the behavior of the fan limit switch as the furnace heats up; presuming nobody has messed with the switch to try to change its settings, it should act as described in the article above beginning

at FAN LIMIT SWITCH TROUBLESHOOTING

This article series answers most questions about central heating and air conditioning system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

On 2021-10-09 by EB - replacing the circuit board resolved the issue of a fan that wouldn't run

@inspectapedia.com.moderator, replacing the circuit board resolved the issue.

the start capacitor arrived and when replaced did not resolve the issue (circulation fan will still not turn on).

I attempted to check if the fan motor is getting power, but not sure if I am checking correctly...I followed black and white wires from safety switch to the board and was able to verify 120v. I removed the black and white wires from the fan motor to the board and set fan to “on”. I do not get voltage at those locations on the board.

I also checked voltage past the transformer is 24v. I tried jumping R to G at thermostat and fan will not run. Do you have any additional advice?

Since there is not 120v at the location on the board that the fan motor is connected when it should be running, I am going to order a replacement circuit board. Thanks for suggestions so far. I will advise if this resolves the issue.

I ordered the capacitor and will double check wires while I wait. Thanks for the link to DMM use and safety reminders.

On 2021-10-09 by Inspectapedia Com Moderator - After trying everything else, it was the circuit board for the blower fan

@EB, Well done. Glad it's been resolved. And thank you for letting us, and other readers, know the outcome.

The most common problems when the fan won't run and when we do suspect the motor itself or its start capacitor, are a poor connection, bad relay, or on occasion a bad control board.

Do keep us posted. That will help other readers.

On 2021-09-28 by EB - replaced fan motor, spinning the fan doesn't get it started

Thank you for the reply. I could not find a reset button and decided to replace the motor. With a new motor in place, the blower will still not turn on

. I did not replace the start capacitor when I replaced the motor. I don’t have a meter to check if the capacitor was damaged too.

I read that giving the squirrel cage a spin while calling for heat or air could be a test to see if capacitor was bad. Spinning the cage does not seem to work. Could my problem still be a bad capacitor? Or should I be checking something else? I know what caused the issue, just not sure how to fix it. Thanks in advance for any advice.

On 2021-09-28 by inspectapedia.com.moderator (mod) - replace the starting capacitor

@EB,

Possibly; a starting cap is very inexpensive - so often a technician will simply try replacing it.

Be sure your wiring is correct and all connections good;

Be sure there is power to the motor;

Watch out: you can be shocked or killed working on electrical stuff, or get fingers cut off in a spinning fan.

DMMs VOMs SAFE USE OF

may be of help

Then check for a burned or damaged control board.

On 2021-09-03 by Katherine - can bad squirrel cage fan cause circuit board to burn up?

If my furnace squirrel caged was frozen, can that cause my circuit board to fail

On 2021-09-03 by inspectapedia.com.moderator (mod) - jammed blower fan may cause circuit board failure

@Katherine,

Possibly; it depends on what caused the fan to jam or seize and whether or not there was local overheating of a motor or control or circuit board.

On 2021-06-14 by Tom R. - air conditioner fan only puts out warm air

What happened to the first part of my problem question? I did all that for nothing and waisted a whole 30 or so minutes of my life on this?

/ only puts out warm air... Have learned much at this excellent site, so look forward to view more tech on this A/C problem now. By the way, it is a heat/A/C pump system for a mobile home. Thank you.

On 2021-06-14 by (mod)

@Tom

I am so sorry if part of your question is missing or lost.

On our end, if the Comments Box software THINKS that the post contains a link, such as text with a.period without spaces it'll block it and send us a notice: we un-block such messages as soon as we can.

It helps me look through the posting database for messages if you remember to post under a consistent name, or if you can tell me an excerpt of words from your lost post.

I've looked through our list of blocked posts and don't see any that we've not un-blocked.

I'll check again

If we are discussing an A/C unit or a heat pump that is no longer cooling, let's start with the "LOST COOLING" diagnostics found at

https://inspectapedia.com/aircond/Air_Conditioner_Diagnosis.php DIAGNOSTIC GUIDES A/C / HEAT PUMP

Or for a more-succinct diagnostic list see LOST COOLING CAPACITY

https://inspectapedia.com/aircond/Air_Conditioner_Diagnosis.php

...

I looked back through posts on our system - there is no more text from you.

Watch out: I've been bashed by this problem before too: in particular, IF you should refresh your browser page while you've typed text into the Comments Box and before you've clicked the "Comment" button, indeed it'll be lost.

It's maddening, and nobody's fault, really.

What I do now is this: If I have a LONG comment to enter, I type it outside the browser, on my computer in a text editor,

then I past the whole shebang of text into a comment and post it.

Of course you don't have to do that. Just don't "refresh" your web page or turn your computer off and back on when you've put a lot of work into text in a comments box but haven't posted it

Sorry

On 2021-06-02 by CJ - outdoor condener unit fan jerky, then stops completely

At first outside AC runs but blower jerking back and forth and would not run. Then all of a sudden fan stopped jerking and does nothing and outside unit does not turn on.

What could have caused outside unit to stop working? Old Frigidaire unit with variable speed motor.

On 2021-06-02 by inspectapedia.com.moderator (mod) - What could have caused outside unit to stop working?

@CJ, quite possibly one of the causes listed above on this page;

Check first for loose bolts or mounts at the fan, motor, or its blower unit cage.

Then check for a motor with a bad or seized bearing

On 2020-12-19 by Darryl A - furnace fan stopped running

I have a gas forced air system. Furnace ignites fine. Fan was only engaging when on auto setting every several cycles of furnace firing up. Became less frequent and now doesn't engage at all. Tried running when fan in an "on" setting.

Worked on several occasions after running fan for a while but no fan no longer kicks back on after furnace fires up.

Additionally, we had a problem late summer where AC did not engage when fan on auto setting but did work when fan on contiuous run setting. Does this sound like a control board problem? Thanks.

On 2020-12-19 - by (mod) - furnace blower fan sometimes won't turn on

Darryl

When the fan doesn't start, does the burner shut off at high limit temp? That's a critical safety feature.

If that's going on the problem could be a bad fan motor or control board or relay - or of course something else.

On 2020-12-02 by Linda Chen - heater fan won't start automatically

Heater fan could not automatically start when we turn on the heater and set the fan as Auto, we have to manually turn on the fan when using heater, however, when we turn on A/C, the fan is automatically on and off.

On 2020-12-03 - by (mod) - blower fan won't start when in A/C mode

Linda

When a forced air fan in an air handler will run properly in cooling mode but not in heating mode AND if you've set your thermostat to HEAT but the fan won't come on then I suspect a problem with the heater's control board.

On 2020-11-27 by Pamela - AC fan doesn't come on when fan switch turned to ON,

Maybe you can give me a little direction....'a/c wasn't working, turned fan to "on", no air from vents. Opened handler cover. Coils were cold/iced. I defrosted and cleaned with coil cleaning foam. Checked and cleaned drain line and dried the sensor. Still no air out of vents.

If I turn off unit at the switch. Then turn it back on, I can hear the thermostat click, and the a/c unit 'picks'... then the internal fins in the blower are moving. I hear a kind of whump ... whump ... whump like some motor is trying to engage but nothing is happening. Even thought the fan inside the unit is spinning, no air blowing from the vents.

Is it time to go outside and work on the compressor part or could it still be something inside at the handler?

Its Friday after thanksgiving, trying to fix this myself if its possible, or at least know exactly what the problem is before I call in the "pros". I have some electronics background and I have changed out the run capacitor ouside a few time. Usually if its that, the air does blow from the vents.

On 2020-11-27 - by (mod) - blower fan runs but no air comes out at the supply registers

If the blower runs and no air is delivered,

un-blocking the coil is a good place to start; but in addition to ice the coil could be dust and debris clogged; Still I'd expect some airflow, just that it'd be weak.

1. Are you sure the blower fan is actually running?

2. Have you made sure the air filter is new and clean?

3. Have you followed the ductwork to be sure that a damper isn't closed and that the ducts are all connected and un-damaged?

4. Is there a broken fan belt between fan motor and fan assembly ?

5. Is the blower fan mounted backwards?

On 2020-09-06 by PETER - fan blower runs in heat but not in cool mode

Fan blower not running on a/c but run on heater, and also couldn't turn on the fan from the thermostat, need help, please

On 2020-09-06 - by (mod) - blower fan runs in heat mode but not in cooling mode

Sounds like a wiring problem or a bad control board

On 2020-08-22 by Anonymous - mobile home blower fan and furnace couldn't "keep up"

My ac air blower went bad in my trailer but for the last 6 months it couldn’t keep up with temp l had it set on, will new one be able to keep up ?

On 2020-07-29 by Tawnie - thermostat fell into the dog's water bowl

The thermostat fell off wall into dogs water dish. Everything works now except blower won’t turn on? Mayb spark plug

On 2020-07-27 by Ryan - burning smell from furnace - fan motor burned up

My blower motor won’t run. I smelled burning smell coming from furnace so I investigated. Coil must have froze up and was overheating. I cleaned coil which was very dirty. I replaced motor and capacitor as well. When I turn unit on the motor just makes a constant noise but doesn’t turn the blower on

. I’ve checked power to board out of board. Thermostat reading 24 volts at board. There is no fuse just a breaker that I checked as well. I honestly don’t what else to check. I will check the switches but am leaning towards control board. Any ideas

On 2020-07-14 - by (mod) - signs of a bad fan motor start capacitor

Mark

Whenever we have an electric motor that will run if given a spin or push I think the problem is probably a bad start capacitor

On 2020-07-14 by Mark Cohen

I have a G51MP Elite Series Lennox Furnace and HVAC unit. The Blower located in the Furnace is not spinning, just hums, although it spins freely when turned by hand. When I turn the Fan from "auto" to "on" on the thermostat , and I help the blower by moving it a little by hand, it runs, but only runs slow. I replaced the Blower Start Capacitor, but the same results occur. Any Ideas, what can cause this?

On 2020-07-05 by Anonymous - air handler won't run

all works good except the air handler

On 2020-07-05 - by (mod) - air handler not working

OK so we're talking about the blower fan that moves conditioned air into your building. Some diagnostic suggestions are above on this very page.

On 2020-07-05 by carole tallent - inside fan not working

I have a all outdoor unit. 2.5 ton the air will work fine through the day, but about 11:00 every night the fan stops. so I turn it off until the next morning,it is driving me crazy

it is a package heat pump all outside, it is the air duct fan

On 2020-07-05 - by (mod) -

Carol

Which fan is stopping:

The indoor air handler fan - discussed on this page

OR

the outdoor compressor-condenser unit fan - FAN, COMPRESSOR / CONDENSER UNIT https://inspectapedia.com/aircond/HVAC_Condenser_Fan.php

On 2020-06-23 by Ken - hosed out the outdoor condenser unit, now it just hums but wont' run

Just bought a home and hosed out condensing unit, probably spraying water on electrical components inside. Fired up A/C and ran fine for about an hour, then it shut down. After letting it dry out a day, I tried firing up and neither furnace nor air conditioner will operate.

A humming noise is coming from the fan blower. Concerned I may have shorted out some wire which led to the fan blower. Sick to my stomach I've worked so hard on this home.

On 2020-06-23 - by (mod) - humming noise from fan blower motor

Ken

A humming blower motor is often a sign of a seized electric motor or possibly a bad relay or control board - that can happen if we get electrical components wet. So sorry, but we've all fouled up something a time or to or ... even more.

If, with power off, the blower motor spins easily I'd try replacing the start/run capacitors, and
before turning power back on I'd be sure every component is dry.

Watch out: if you're not familiar with proper safe electrical work you could be shocked or killed.

Also search InspectApedia.com for ELECTRIC MOTOR DIAGNOSIS for some easy tests

On 2020-05-26 by Darrell - blower fan works in heat but not in A/C mode

Blower motor works on heat cycle but won’t when switched on to A/C cycle? Fan motor working outside on unit but not on furnace? I’ve had door on and off turned breaker on and off too. Wiring looks ok capacitor?

On 2020-05-26 - by (mod) - blower works only in heating mode

Darrell

If the blower motor works in heating mode I don't think its failure to start in cooling mode would be a blower motor capacitor failure.

More-likely there is a wiring error (if the blower motor has never worked in cooling mode)
or
a control board or relay failure (if the blower motor used to work in cooling mode)

On 2020-04-23 by Luis - York blower motor does not come on

This York blower motor does not come on, the power was verified, if I manually press the contactor in it works , but not on its own , I’m not getting 24 volts to board

On 2020-04-23 - by (mod) - York blower motor won't turn on

Luis

Good first diagnostic steps.

If you jump the thermostat terminals the burner should start first; the blower won't come on until the plenum has heated-up.

So: on a call for heat, does the burner ignite? (Is this gas, or oil?)

Also, if there is a manual ON control on the limit control, turn it to FAN ON - if the blower runs then the problem isn't the blower itself.

More diagnostics are in the article above.

a

We have an electric furnace (Trane). We just moved into our building, so did not know if the heating unit worked last year or not. We have had trouble with it since we turned it on. We have been told just recently a belt was loose and the system was in a hard lock.

He tightened the belt and reset the system. The next morning we came into the heat not working. The thermostat is set on 71, but it was 64 when we walked in. So could this mean that our unit is locked up again?

Question: blower fan runs if I give it a spin

2019/10/25 Dsmith 10

We have a Nordyne furnace Model #PGC2TC060D24B. The Blower # is 622636. When we put the fan in run mode, the fan will run sometimes and sometimes not until I spin the wheel. It is doing this when we try to run the furnace and air also.

Where is the capacitor on this motor? It is not on the outside of the motor. Do you think it is the capacitor?

Where is the capacitor located on a #622636 motor on a Nordyne furnace # PGC2TC060D24B furnace It is not on the outside of the motor. The blower will run sometimes when the thermostat is in the run mode and sometimes it will not run until I spin the wheel.

Reply:

I don't know this furnace exact- model, D.S. nor could I find your model number - have you got the IO Manual for it? If not we can help find one - that'll include wiring diagrams and parts lists.

But yes in general if the motor will run when you give the blower fan a spin then usually the problem is the starting capacitor (if present) OR a bad start relay control switch.

On 2019-06-30 by Tom - older trane unit indoor unitcircuit breaker is stuck in the on postion - indoor unit nothing comes on .

@tom, can the breaker that is stuck in the on postion not let the air handler come on

I have a older trane unit indoor unit breaker is stuck in the on postion - indoor unit nothing comes on .

have ck all breakers.outdoor unit when contactor is pushed in it comes on

On 2019-07-02 by (mod) - does circuit breaker prevent the fan from turning on?

Tom:

From just the comment that you've posted I don't understand the situation except to give you a very serious warning that if you have a circuit breaker that is as you describe it stuck in the on position that's extremely dangerous risking a house fire.

Watch out: a "stuck" circuit breaker is unsafe, risking a building fire. Ask your electrician to replace the bad circuit breaker.

Then ask her to check for a short or electrical failure on the electrical circuit that the breaker is supposed to be protecting.

On 2019-06-14 by Harry - IFM comes on only when White Rodgers fan switch set to manual ON

The IFM will only come on when the White Rodgers fan limit switch is moved from auto to manual on .doesn't matter what position thermostat switch is in.

On 2019-06-19 by (mod) - Blower only works in MANUAL mode

Let's start with a review of the causes listed above on this page. Please take a look and let me know what you think.

On 2019-06-07 by Rich - fan blows fuse when I switch to cooling mode

My HVAC when on fan it works, but as soon as I switch over to AC it blows the 3 amp fuse. Any help would be appreciated.

On 2019-06-08 by (mod) - A/C blows fuse: bad compressor or fan motor

Sounds like a seized compressor motor or Mis-wired control

On 2018-10-14 by (mod) - things I can check on my AC unit when The blower fan is not coming on.

By private email:

I would appreciate any help or comments on things I can check on my AC unit. The blower fan is not coming on. There is a 3 amp fuse in the wiring system that I have checked and it is good.. something tripped the breaker on the unit itself. I tripped it off and turned it back on.

. the system came back on but there is no forced air coming through the vents and the condenser coils began to freeze up almost immediately. The unit has a squirrel-cage fan and it will not come on. With the breaker in the main panel switched off I reached in and the fan spins freely..

I then switched the main breaker back on and I can hear a “humming” but the fan won’t spin.. is it possible that the start-up capacitor and/or starter relay has gone out?? Again, any help would be greatly appreciated.. will be 90* hear tomorrow and my wife will be here with no air this week if I can’t get it going tomorrow..

Reply:

"something tripped the breaker on the unit itself"

tells us that there was an over-current or short circuit; that could be a failing motor, low voltage, or a failed or shorted switch, control board, relay, or wire.

A service tech would probably inspect for something visually obvious: damaged, burned, loose, and then follow the current path through the equipment.

Watch out: you could be shocked or killed if you don't know how to follow those procedures safely.

On 2018-06-06 by Steve - blower motot hums, won't start

I replaced start capacitor but blower fan will still not start by itself, just hums. I was able to start the fan while humming by pushing squirrel cage with screwdriver.

On 2018-06-07 by (mod) - sign of a bad motor capacitor

Usually the situation you describe is traced to a bad start run capacitor, bad fan bearings, low voltage, or one of the other causes discussed in the article above on this,pge.

On 2018-01-14 by David Turner - burner runs but fan won't turn on

I have asked similar questions, but cannot find those or the responses...so..I have a 20ish year old "inter-city" (international comfort) oil furnace.

Furnace comes on (fire), but fan will not. There is a manual switch at the fan, and that starts it right up, but it will not come on as a response to furnace which shuts everything down.

I have installed new start/run capacitor, but no help. Jumpering "G" to "R" @ board causes fan to "hum" but not start. This thing is driving me crazy & it's cold. Crawl space is tight. Have had two "reputable" service men come, but neither was helpful.

One didn't seem to know what he was looking at & the other was either illiterate or a liar as he took down serial/mod #s and said furnace could not operate in "that position" and he would need to "change burner position" for $3-400, but since so old I should just replace.

Was installed when house was new w/no trouble for 20+ years also labled in 3 different places within inches of "#s" is instructions on how to install in updraft, downdraft or horizontal positions.

Cad cell clean, filter new, nozzle good, furnace lights....HELP ??!! Thank you.

On 2018-01-14 by (mod) - watch the limit switch dial to see why a fan isn't working

David

Watch the dial on the limit switch on a call for heat.

If the fan limit control dial rotates as the plenum heats up (as it should) the dial will rotate past the FAN ON temperature. At that point the blower fan should start.

If the burner is running but the fan limit dial never moves then the problem is in your case probably the limit switch itself.

Other things we check are the fan start/run capacitor and the fan motor itself as well, of course as the blower bearings and movement. Since your fan starts and runs in manual FAN ON mode I suspect the limit switch.

Humming noises usually point to a failed motor or a bad starting capacitor

On 2017-11-21 by Thomas - bad zone valve on water-to-air heating system

I was able to figure out the issue and it turned out to be a zone valve. I am not new to HVAC but also not a professional and haven't messed around this system much.

The unit is inside a bathroom ceiling servicing a hotel room without an access panel so i tried to do as much diagnosing before cutting a hole in the ceiling and installing an access panel to the area of the AHU valves.

In this system the heat zone valve not only open and closes the tempered water but also powers the blower unit.

I am working on diagnosing why my heater wont turn on, the blower motor will run when on cooling but not for heating. I have two boilers running with a boiler pump and know my heat pipe is up to temperature but the fan wont start up. Is there a fan limit switch just for heating?

On 2017-11-23 by (mod) -

Thanks for the follow-up Thomas that will help other readers. I think that you are describing a water-to-air convector unit and a fan that wasn't turning on.

...

Continue reading at FAN LIMIT SWITCH TROUBLESHOOTING or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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BLOWER FAN WONT START at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING FURNACES

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