What is the deal with A/C units and tonnage? How is a system sized properly?

Ok these are some quick and dirty rules of thumb when describing A/C tonnage, BTU's and how to size a unit for a home.

One ton of cooling = 12000 BTUS and is designed to cool approximately 400 square feet of living space.
So, if you have a 2000 square foot home you might have one 5 ton unit or two units a 2 and a 3 ton.
These are rough numbers so your results may vary.  When your home was built someone (hopefully) did a calculation to determine what size unit to put on that particular home.  If the home was made of glass then obviously the unit would be sized larger, for example.  I live in a 3200 square foot home but get by with a 3 ton split and a 3.5 split system.  A little undersized but I have returns that go under the concrete slab and 2x6 framing with good insulation.  My system is sized properly.

Now why not just upgrade the unit and stick a couple of 4 ton units at my place? I mean more is better right? NOOOOOOOO!  My units run often during the summer but they turn on and stay on.  If I upped the size of the units then they would 'short cycle'.  A fancy way of saying turn on and off all the time.  If I selected 77 degrees at the thermostat and the unit kicked on at 78 it would pull down to 77 in a hurry, no doubt.  But, and here is the kicker, it would not run long enough to dehumidify the air and thus run back up to 78 in short order and the cycle repeats, over and over again.

The hardest thing for any motor, and I don't care if it is your lawn mower, car, ceiling fan or A/C unit is to turn on.  The amp draw of an electric motor is higher at start up to overcome the torque necessary to get up to speed. Example, my compressor will momentarily draw 60+ amps at start up and then run at 14 amps.  That is a lot of heat in a short amount of time and motors HATE heat.  It is their Achilles heel.

Last how can you tell how many tons your unit is.  Look on the name plate on the unit.  You will find on the model number a few numbers and letters and then typically a 0 followed by a number divisible by 12.

Example:  Lennox model 13hpd 036 230

The 036 is the giveaway that this is a three ton unit - it moves 36000 BTU's of heat in cooling mode.  A five ton of the same model Lennox would be  Lennox model 13hpd 060 230.

You may have a unit that you think is undersized.  In Phoenix it runs a lot in the summer but the rest of the year it kicks on and off as needed.  This is ok as long as the unit is mechanically sound and in fact good for it.  Remember the starting and stopping is what is bad for the unit.  Airflow ect.  are totally different issues.

For more helpful tips and questions answered visit my free A/C help site at http://www.thermal-medics.com/ and please, call me or email if you have any questions..

Got a leak in your unit? - Odds favor these culprits from thermal-medics.com

Ok you notice your A/C is not keeping up to the desired temperature selected at the thermostat.    Or it may just be running all day just to keep your home cool.  A common problem we see out in the field are leaks in the refrigerant system. 

Let's get this straight first off, the refrigerant in your system is a closed system.  It does not use up any gas to run but the level should stay the same.  In fact you can look on the nameplate of your unit and find out how much refrigerant and what type you have if you wish.  You will start to notice a degradation of your units efficiency when it is approximately 2 lbs (give or take low).   Also there may be enough refrigerant to run your system fine in April or May but in Phoenix in July it just can't keep up.

Split systems have more leaks than package units.  That is just a fact.  There are copper pipes that have to be brazed in the field during installation and that always will increase the likelihood of leaks.  Package units are just that, from the factory, sealed and typically pretty solid.

An easy DIY troubleshooting technique to see if you have a leak is to feel the refrigerant pipes.  The larger one (suction line) should be cool to cold to the touch and the liquid line (smaller one) should be warm to hot.  If the pipes are lukewarm or if you have frost on the suction line a refrigerant leak may be the culprit.

Where do leaks happen?  Here is a short list that the odds favor.

Schrader valves where Techs hook up manifold gauges
Service valves (next to schraeder valves)
any brazed joint
indoor or evaporator coil (rusting out/pinhole leaks)

You can do a visual inspection of these areas if you choose.  Another dead giveaway is oil stains.  Oil travels in the refrigerant and any leak will leave traces of oil.  For example, the schrader valve caps have oil in them, etc.

Techs will use a nitrogen charge to pressure test the system and sometimes use a dye as well.

How are leaks repaired?  Once found they can be brazed shut, shcrader valve cores replaced and in the case of evaporator coils they can be replaced or you can use a can of Super Seal in the system.  I have seen 60 to 70% success rates with this product.

For more help or to ask specific questions email me at info@thermal-medics.com or visit the free help website at http://www.thermal-medics.com/.

Take a tour of the outdoor unit of a heat pump

Here is a quick video of an outdoor unit of a Lennox 3 ton heat pump.  It will give you some idea of the terminology used and can be a reference for problems and repairs. Enjoy..

For more free help and questions answered visit http://www.thermal-medics.com/   Call or email anytime.  Get educated, get informed and save money..

more free A/C videos here

Hands down the worst A/C story ever......

Ok, first of all I know this is not some urban legend in the HVAC world, but it easily could be.  I know this individual and I believe his story.

Back up 15 years or so in Phoenix during a hot summer.  This fellow was just out of trade school and got his first job at a small Dad and son outfit.  Well, of course, he was nervous and wanted to make a good impression.  He rode with the dad on day one. (another story-another day) He rode with the son on day two.The first call was some routine, low freon, gas-n-go.  The next was one for the ages.

They knocked on the door and an elderly woman answers and says her A/C is blowing hot air.  Granted it is in June so things are heating up quick and she only has one unit.  During the course of the discussion the 'son' finds out she is a widow recently and she does not know much about A/C (except it dosent work).  Well the two pull the ladders and go up on the roof for a look.  Package unit, pretty straightforward.  The new guy looks in from the top and notices a lead on the compressor is burned off.  He tells the 'son' thinking, "Wow, I just proved myself."  The son grunts and says lets go on back down. He tells the new guy to go wait in the truck while he talks to the customer. When the son returns he says lets go out and get a bite to eat and get a couple of things.

By now the new guy is confused. First they stop for a burger and the son pays.  He gets a whole speech about how tough the business is, blah blah blah...Then they go get the local newspaper from the convenience store.  Next they stop by a hardware store and get two cans of black lacquer spray paint.  (Oh no, you say but yes they do).

They return to the home, remove the top, fix the wire for .25 cents and layout the newspaper.  They spray paint the compressor a shiny new black and put it all back together.  $650 later they are out the door with a 'new compressor' installed.

You are asking does this kind of $xxt really happen? Yes it does.  Your job is to get educated, ask questions and be involved.  I got into this trade after my parents were scammed by some local dirtbags. Do I want to get even, yes.  This is why I write this stuff down and share it.

By the way did you know if you have only one unit in your home and have small children or elderly folks living there some, reputable, companies will prioritize your call. Make sure if you know someone who is older and lives alone has that information....Anyone can contact me at http://www.thermal-medics.com/ or pick up the phone to call.  My phone number is on the website.  I don't care if you call or email from Fargo or Florida I will get back to you and I will answer your questions.  The website and this blog are FREE for anyone, DIY, homeowners, general questions or anything related to heat pumps and A/C units.

That time of year for the old A/C 'tune-up' calls...ughhhhh.

Ok everyone, I have a little video on the old A/C 'Tune-up" deal.  Usually the only thing that is getting tuned up is your wallet.  Preventative maintenance is something else and I will post a quick list of things you can DIY or ask about when you have it done.  Enjoy...

Is your A/C giving you "static"??

In response to Mike V. in Lakeland Fl. a question about static electricity and HVAC units.

Here in the Valley of the Sun we have notoriously dry weather and low humidity.  A complaint I run into now and again is usually offhand but very telling.

"We have so much static in our house, we are always shocking each other."  Of course the kids love it but here is what may be going on and how to correct it.

Your Air Conditioning system is designed to move heat.  That's it.  During the summer it moves the heat from indoors to the outside via the refrigerant and then blows it into the air by way of the condenser fan.  Water carries a lot of heat.  When the humid air blows past your evaporator coil that is in the 40 degree range guess what? The water condenses and flows (hopefully) outside.

Now the idea is for that de-humidified, cool air to travel back to the conditioned space and you to go about life.  Here is where the 'static' starts.  If your blower motor (in the air handler or on the rooftop on a packaged unit) is set to too low a speed the air from the return stays in contact with the coil longer.  How much longer?  Who knows, but it is just long enough to remove too much humidity and make your living space dry as a bone.

What can we do?  Simply speed up the blower motor.  Usually the fan motor has multiple speeds and the fan can be sped up to the next faster to stop all of your static problems, that is, unless your kids need something to do indoors in the summer!

For help on changing your blower speeds yourself or any A/C or Heat Pump related questions you can write me here or at http://www.thermal-medics.com/.