Domestic hardware helpline

[Sibling Zono (anon1mat0)]

Ok, this is a plea for help, most likely from the expert sibling on all things AC (I'm looking at you Bob ). The breaker for the AC compressor jumps. A lot. In fact at this moment it simply refuses to go up despite the fact that I replaced the breaker for a higher capacity one (30A to 40A). More so, even after turning the AC off the breaker still jumps as if something were drawing power from it. Yesterday I had the same problem and I replaced the breaker thinking that it was faulty but what caught my attention is the fact that it was failing just after midday when the heat is at its peak (~92F).

I wonder if this is a problem with my AC (perhaps shorting?) or with the power coming into my building simply overloading (it shouldn't happen but why in the afternoon?).

[Bob in a quantum-state-of-faith]

Ok, this is a plea for help, most likely from the expert sibling on all things AC (I'm looking at you Bob ). The breaker for the AC compressor jumps. A lot. In fact at this moment it simply refuses to go up despite the fact that I replaced the breaker for a higher capacity one (30A to 40A). More so, even after turning the AC off the breaker still jumps as if something were drawing power from it. Yesterday I had the same problem and I replaced the breaker thinking that it was faulty but what caught my attention is the fact that it was failing just after midday when the heat is at its peak (~92F).

I wonder if this is a problem with my AC (perhaps shorting?) or with the power coming into my building simply overloading (it shouldn't happen but why in the afternoon?).

A-HA!

Several things cause a ramp-up in power requirements, with A/C's

The simplest thing to fix is a dirty outside unit.

No, seriously!  If the outside unit is dirty, or plugged up with dirt/lint/junk, then air cannot pass properly over it's fins, and this causes a rise in the "head pressure" to as much as 300psi or more.

This rise causes the compressor to work harder than it ought, and since it's most likely and induction motor-- it will simply "demand" as much power as it "needs" regardless of it's actual rating-plate.   (in fact, high- power induction motors are exactly the same as low- power motors, except they have larger wires, to handle the higher amps/current.  The lower power motor will work at the higher load-- until the wires melt, that is...)

So.  Take a garden hose, and squirt into the fins until the water flows freely through them, and is clear of dirt and debris.  Careful!  Too much pressure can bend the fins-- not good.  Use your thumb over the end, until you get a feel for it. You may need to open up the top-- if that intimidates you, just hose in from the outside.  Let the breaker stay off during, but if you forget it won't hurt anything.  (these are made to be wet-- they are outside afterall).

Also-- inside, check if your air filter is dirty.  This can make things worse, but won't create your symptoms directly.

.....

Observe your outside unit, after you've washed it (no need to let it dry).  Is the fan on top turning properly?  Is there a lot of air coming up out of it?  Is that air cool, warm or hot?  (a clue, that)

If the motor that turns that fan is dying a slow death, you get the symptoms you describe.

What happens is the fan quits or turns slowly.  Again, you get excessive head pressure on the compressor, causing it to draw more and more power to keep pumping.   Eventually, it draws enough to trip your breaker.   Meanwhile, it's off, and the fan-motor cools off and starts working again.   

Rinse and repeat cycle.

So.  Watch that fan over a period of 30 minutes or an hour.  Is it spinning rapidly?  (making a nice blur of the blades, not unlike a standard window box fan). 

Is the air really hot?  It should be warm, only.  About 10-15 degrees warmer than the ambient air, actually.  If it's cool, then your compressor is not doing it's job or not running at all (unlikely, as you keep tripping breakers, but not instantly).

If it's hot-- really hot, then the fan is not drawing enough air through the unit-- due to bad fan motor or clogged fins on the unit or both.

If the fan does not turn at all-- you've discovered it right away.

If it runs for a time, then slows down or quits-- again, that's the issue.   Watch-- it may be overheating, and cycling on and off (it likely has a thermal thingy that makes it do this).

What is the fix, if it's the motor?   Two possible things:  Change the motor's capacitor, or change the motor.   Or both.

If you want to just change the capacitor, it's easy as pie.  Turn off the breaker. (DUUH!)  Open the panel on the side of your unit-- look for the panel where the wires go into.  It'll be that one, or the one next to it.  Inside, you'll find lots of dirt and spider-webs.  Ignore those.

Look for a silver or black "can".  It'll either be a cylinder or an oval shape.  It'll have 2 or 3 or more wires attached.  They have push-on type connectors.  Make a diagram of which wire goes to which bit. OR take a photo with your cell phone's camera.  Or both.  Can't be too careful, here.

There MAY be two cans-- one for the compressor and one for the fan-motor.   The smaller one is for the fan.   

The can(s) have either 2 or 3 terminals.  If there's 2, it's simple--- look for the small can, remove the wires, take it to an electrical supply house, and obtain an exact replacement.   Plug the wires back in, and test.

If there's 3 wires-- a diagram is essential to be sure you get the wires back where they ought to be.  But, again, remove wires, take can to supply house, and get exact replacement.   Replace wires, test.   Make a note of the markings on the can, too.  The terminals on the can will be marked "C" "H" "F" or "Com" "Herm" "Fan"  or "Common" "Compressor" "Fan" or some combination of these.

Note which colored wires go to which of the 3 terminals-- IT MATTERS.   FYI, if "H" or "HERM" is used, then "C" or "COM" means "common", and is common to both fan and compressor.   Rarely, you'll see the actual word "compressor" on the cap/can.

If there  are 2 capacitors, and you can't tell which is which-- just replace both.  These are cheap ($3 to $10 US) and replacing both hurts nothing.   Just look at the print on each can, and be sure you put the correct replacement value on the correct wires.

Hint:  your fan's capacitor likely needs 5mfd or 7.5 mfd or 10 mfd.  99% of fan motors use one of these.  Rare ones use 3, 4 or 6 mfd or sometimes 12mfd.  These are rare.   

Your compressor uses a large value, from 30mfd to as high as 60 mfd.  Typical is 35 to 40 mfd.

If the motor works-- you're done.  It is 70% likely that if the fan-motor IS the issue, then the capacitor is at fault.

If the motor STILL does not work correctly, you'll need to replace it.  No worries-- you HAD to replace that cap with the new motor anyway-- NEVER re-use an old capacitor-- they are too cheap to reuse, and they DO fail.    Even if the old one is a 3-terminal combined one, you should replace it.   The compressor won't mind a new cap...

The motor is 99% likely to be a 1/3 hp (or smaller) 1075 RPM 208/220 volt motor.   Unless your unit is less than 1 year old, or is a very odd brand.

The motor is a bit more involved than the capacitor-- but not really.  Just take a picture, or draw a diagram.  Look on the old motor's label for what it is, and buy another just like that.  You may want to buy the motor FIRST, before removing the old one, so you are more familiar with how it goes back together.

Ask/PM me if you've questions in detail.   

I can give you a basic wiring diagram, if you like-- they're all pretty much the same.   There are minor variations you can do, especially if replacing the fan motor-- like splitting the capacitor from a combined one into two individual ones.  (I typically do this step myself-- I'm not fond of combined caps....)

Good Luck! 

Remember-- you CAN NOT make things worse, if it's broken anyway!   

[Sibling Zono (anon1mat0)]

Thanks for your detailed response (and concern). Reading the whole explanation I'm guessing I was having problems either with the compressor or the fan, but at this point whatever was about to die died. For what the guy told me, if the compressor is gone it doesn't make sense to replace it (the guesstimate he gave was ~$1.2K) compared to the whole unit (he suggested ~$1.6K, I imagine/hope those prices include labor  ). My next question is if that sounds right...

[Bob in a quantum-state-of-faith]

The compressor failing would also exhibit the symptoms you describe-- especially a short-to-ground of one or more winding.

And, he's right-- we never replace compressors, except under warranty (where the cost of the compressor is covered, and it's just labor).

I put in a replacement unit the other day for $1,500 [total] so his prices are close.   Ask about the efficiency of the replacement, and if it will match correctly with the A-coil inside.

Most new outdoor units manufacturers require a new A-coil, to ensure adequate (and meeting the new legal requirements) efficiency.  These numbers are measured in SEER (I don't remember what that stands for-- think "MPG" for A/C units).

13 seer is the minimum.  15 is better.  Much higher than that, and you'll have to pay out the proverbial backside, and it'll take years to recoup the extra $$.   Your old unit was likely 10 seer when new, and probabily around 7-8 towards the end of it's life.   Higher is more efficient, translating to less $$ for the same quantity of cooling effect.

And yeah, 1.2k is about right for a replacement compressor-- the compressor itself wholesales between $500 and $800, depending.  But, the labor is much higher than replacing the unit-- because it's a pain in the arse.  AND you have an old unit with a new-ish compressor.... kinda like putting a brand new engine in a rusty old car with a shot clutch, and cranky transmission....

FYI, if someone insists on "just" a replacement compressor, we always quote it so that it costs as much as a new unit..... (unless it's warranty, as I said).  We hate replacing compressors....    If they don't like our prices, they are free to get someone else.  And please don't call us to come service it later, too....