Air Handler Repair FAQs

Rodent damage
Blown Fuses
Door safety switch voltage
Repair vs replace a TEV or capillary tube

Interesting AHU Blower Unit FAQs

Can a mouse in the air handler damage the blower fan?

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 2018-05-26 by Steve

by (mod) - Yes, off-balance fan cage damages fan bearings

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.

Air handler control board fuses blown

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 (May 18, 2014) Gary Matthias

Reply:

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.

What is the air handler door safety switch voltage?

on the air handler door safety switch , would like to know what volts is suppling the switch and where thanks. 1 Nov 2014 Anonymous

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

Anon,

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.

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.

See BLOWER DOOR SWITCHES found also

at A/C - HEAT PUMP CONTROLS & SWITCHES

How to seal attic air handler leaks

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? (Feb 20, 2015) Valerie

Reply:

Valerie,

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.

Is it economical to replace air handler parts or not?

Anonymous said:

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

Reply:

Anon

Replacing the air conditioner or heat pump refrigerant metering device usually means replacing a capillary tube or thermostatic expansion valve (TEV).

That's a discrete part that's reasonable to replace rather than replacing the whole system provided the rest of the system is in good condition.

So in sum, it depends on the equipment age and condition. What does your HVAC service tech say?

Question: track down source of moisture, rust, corrosion in air handler

I have Unico mini-duct system in my attic. Every winter, the fan motor and shaft accumulate rust. I live in a very cold climate in winter (Vermont). Last year, I had the motor replaced and this spring, there was rust on the motor again (no visible rust last Fall when I closed the unit up for the winter). - JL 2021/07/01

...

My technician agreed to problem cannot be caused by the dryer venting back up into the attic.

The Unico system is pretty air tight due to it being a high velocity system.

He also did not think the two outlets that I never open would be the source of condensation for the winter months. Nor did he think running the fan in October just before I close it up could cause excess moisture to accumulate since the air is pretty dry in Vermont (low humidity) in October.

So we still have a mystery. He said the unit was completely dry inside today despite the fact it was hot and very humid here yesterday. - JL

So we still have a mystery. Thanks for your suggestions and comments though. If we ever figure this out, I’ll let you know.

Moderator reply: sources of water in the duct system

Thanks for the follow-up, do keep us posted, as what you find will certainly help other people too.

In investigating, start at the point of most-concern such as rust or corrosion, and follow the water or water indicators, stains, signs, rust patterns, etc.

See our full conversation now found

at WET CORRODED DUCT WORK

Where do I get a wiring diagram pdf for a York Air Hander Unit?

Hi, I´m working in a small project, but I need the diagram pdf for an Air Handling Unit (heating)
the model that I could find is:
YORK
MODEL G+FD060S24A
SERIAL NUMBER: EGHS622778
5005 YORK DRIVE

If you can provide me with this information, I´ll be so grateful
Thanks On 2020-04-25 by JOSUE ROJAS

Solution by (mod) - York HVAC Manual

Josue

See if this manual helps you out

https://inspectapedia.com/aircond/Unitary-York-Manual-036-21002-001-b-0600.pdf

as from a quick look at the equipment table that guide, now from Unitary Products, includes your York MODEL G+FD060S24A

Can the air handler blower unit's cooling coil be replaced?

Can the coils in the air handler be replaced or do you need to replace the whole unit? On 2020-02-19 by lowell

Answer by (mod) - yes but check the cost

Yes, an evaporator coil in the indoor air handler can be replaced.

But particularly if your air conditioner or heat pump is an older unit or one likely to be facing other repairs soon, I would compare the cost of the replacement job to the cost of whole unit replacement.