Whenever the AC kicked on in the past, I would hear the unit outside start running, immediately followed by what sounded like a motor/fan under the house (don't know anything about HVAC systems or how they work, sorry if I sound stupid) and cold air blowing through the vents inside 1 second later.

Over the past couple weeks, I've been hearing the unit outside start running like normal, but the motor/fan sound from under the house is extremely delayed. It makes a loud "humming" sound for several seconds, then starts up very slowwwwwwly, taking another 10-20 seconds before it finally gets up to full speed and air starts blowing inside.

Then this morning, the "humming" sound went on for a LOT longer before the motor/fan thing under the house started running, and when it finally got up to speed and blowing air, there was a faint chemical smell coming through the vents (like burning metal?) that went away after a few seconds. When it came on the second time, the humming went on for even longer and the smell was a lot stronger. When it tried to come on the third time, the unit outside was purring away like usual, but the motor/fan thing under the house just kept making the humming sound for at least a couple minutes, so I turned it off.

How screwed am I? Is this like a $100-$200 motor I can buy and install myself, or are we talking the whole system needing to be replaced? System is original to the house, so it's probably creeping up on 20 years old.

Can you provide the make and model of A/C unit, furnace, and air handler?

I'm not an HVAC tech, but as an electrical engineer, I can tell you that motors require a capacitor to get them started. Your symptoms sound like the capacitor died. The smell could be the capacitor, or it may be the motor burned up its windings.

20 years old? You're on borrowed time.

Call an HVAC company out. May just need the air handler motor replaced. But no matter what start saving for a new system.

And start saving for a new system


beat by 20 seconds....  

Unit outside says Trane XE1100 High Efficiency Weatherton Heat Pump

Also just noticed the refrigerant line is frozen solid


Turned the AC off and turned just the fan on to try to thaw it out. scratch that, that's what some websites said to do to thaw it out, but I guess the fan uses the blower motor or whatever the thing under the house is called. It was still just humming and never came on, so I turned everything off.
Wife is a little bit cold natured and hates the feeling of air blowing directly on her , so she had half the supply vents in the house closed. Read that can cause problems by restricting airflow to the evaporator coil, so I opened them and went ahead and replaced the return filter too.

We had to have the freon refilled (recharged?) last year and the guy said it probably has a small leak somewhere, but with the age of the unit, it wasn't worth finding and fixing the leak. I would think it's just low on freon again, but the way whatever the motor/fan thing under the house is making a humming sound and not coming on and blowing air like it should, it makes me think that needs to be replaced.  I had an indoor blower motor (in the part that's under the house) replaced 3 winters ago because it stopped blowing heat...does it use the same blower motor for AC and heat, or 2 separate ones?

Same motor for heat and A/C

Sounds like the capacitor on your circulation fan is bad.  I just replaced mine.

It set me back a whole $5.50

It's usually located right on the fan housing.

Fingers crossed. That would be WONDERFUL if that's what it is.

Sounds like the bushings [bearings] in the blower motor have seized...

That's the first thing to check. See how hard it is to rotate by hand...

If so, Grainger probably has a motor...

Been down this road several times...

Then I bought a bushing kit and bushing line reamer and save lotso $$$





Take good care of your system and you can make it last far longer than folks might think...

One place I have, the heat pump was installed in the late 1980's... I take GOOD responsible care of it. I also take units similar and save the parts from them...

I could like run this unit another 30 years...


This said, I have a brand new replacement unit waiting to be installed once I chose to do so...

Oh, look at the part number of the blower [if one is needed] and you can probably buy it for 1/2 to 1/3 the price a local dealer would charge.

Google the PN and also search on eBay.

It's not unusual to have a small leak in an AC unit and add refrigerant yourself from time to time...

Beats the hell out of replacing the whole thing...


Decent leak detectors aren't that expensive.

Also, put soap solution on the charging ports [and service valves if yours has them] and see if the leak is there...


My experience with service techs is that too many are filthy lying crooks...

If you search my posts over the years you will find MANY examples of mine and friends' experiences...

I didn't read all your posts. If the OD unit froze up, it might be because of the air handler issue...

Most likely, your cap is bad on the blower motor.  The line ices up (actually the whole inside coil ices) simply because you arent getting airflow across it.

$10 to $20 depending on where you buy it.  Or, $50 from an AC guy plus a service charge, and labor.  I have seen HVAC guys charge $250 for a cap, because they sell a "full inspection" plus the emergency service call.

Crap, harbor freight sells a DMM that has a cap check function  IIRC  for less than $30.

I wouldn't let a tech within a 1000 feet of my AC's unless I was too poorly motivated to pursue the issue...

In that case, I'd go to WalMart and get a large can of BUTT LUBE




Or you can swap the cap from the OD unit into the indoor and see... Pull the fuses or flip the breaker for the OD unit during this test....

Capacitance vlalue may be off but for an indication, no big deal...

EVERYONE is sooner or later going to have these issues with their AC

Folks should plan ahead with parts and skills accordingly, unless they don't mind spending a lot of $$ and likely getting ripped off...

You're on borrowed time with a 20-year-old AC system.  

You'd be amazed how long you can keep these things running if you are motivated to learn and fix...

As well as respect the unit and treat it carefully...

Like I said, I've got one running for 30 years right now...

One ran from 1963 to ~1996,  

Several ran  from 1973 to 2006, sold the place, don't know how many years longer...


Commercial big crappy [stay away from Carrier]  rooftop units, 12 of them on a bldg. I built, ran from the 1980's and as far as I know some are still running...

Did or supervised all my own service...

Some of the older units, while not all that efficient, are very durable. From what I have seen, newer units are more efficient but don't last as long, typically.

Seems to still be working (barely). Gonna try to track down some parts today, and someone local who knows more about this stuff than me, but I don't know how successful that will be with having to work until 5.

The refrigerant line keeps freezing up. I'll turn it off and let it thaw out, then turn it back on. It'll make the humming noise for a lonnnnnnnng time before finally coming on for a little while, and then the refrigerant line is frozen again.

I hate to keep running it like this, I've been taught to turn stuff off immediately when it's not acting/sounding right, to keep from messing it up worse. But with 100° temps and having a pregnant wife and a toddler, I don't really have a choice .

Looks like she's over 20 years old actually



Thanks for the help, guys. I really appreciate it.

2.5 tons 11 seer r22 heat pump

It's a capacitor, [on air handler side]  shut the damn thing off until you replace it, discharge the cap, [screwdriver twixt the connections] pull one of the strap screws, note the mF rating, go to HVAC/electrical store, buy one for a few bucks [likely a 7.5-12.5 mF rating on it most likely] install it, turn power back on.

You need the model and serial off the furnace or air handler in the crawl space

Will do. It's off now.

Well that was a spiderweb nightmare from hell

Shoutout to the plumber who wrapped the water pipes all around it, making getting to it turn into a tryout for American Ninja Warrior

Buy a window unit and use it to keep a room cool for your wife while you fix the unit. Keep the window unit for future emergencies. With an old system you'll probably need it again.

Man I would not want my air handler under the floors.  Is that a common practice?

Around here they are in a closet, or in the attic.

You will have to remove the panel to access the blower motor.  The blower is located at the opposite end of the evap coil.  Once you get the panel off, you can pull out the cap and inspect it.  Buy a new one with same capacitance and give it a try.  If that doesn't work, you'll need a whole new blower motor (and a new cap for that one too).

My last house was that way. It worked fine but getting under there to clean the coil and do maintenance was a mild pain. The crawlspace was plenty big enough but I wish I had designed that house differently.

The house I just built has the furnace/coil mounted in a room in the basement. I much prefer that way.

I'd rather have it in the crawlspace than the attic though!!

OP, have you tried to move the blower by hand to see if the bearing sleeves are OK???