How cold should the air be as it comes out of my A/C vents? It's at 60F,
but my A/C has been running non-stop since temps hit > 90F here in Orlando.
I'm pretty sure it's a testament to needing more insulation (23 year old
house, original cellulose, thin in areas), but I want to make sure my A/C is
blowing cold enough air as well.
To those who responded to have it checked.. It was checked in October, so
it's < 1 year. It got a full cleaning of the compressor coils and needed a
little refridgerant. The coil can use a little bit of a cleaning, but the
unit is so old, I'm suspecting it will go out entirely, and I wasn't going
to spend $300 to have the coil pulled. My main concern is it blowing the
proper amount of cold air, which it appears to be doing.
Superheat, or Subcool. A good tech can actually charge a system without a
manifold gauge. Pressures mean little, give a BASIC understanding whats
going on, and are but ONE tool to use. They can show you when you have a
valve fluttering, or stuck, but anyone that pops up with a tank of
refrigerant, and a manifold and hooks up, throws some juice to it and comes
in and charges you for Xlbs of R22, or R410 (Puron) and didnt use a scale
for starters, you owe NOTHING.
No scale, no way to know if he put in an oz, or a pound.
Some, like Goodman on the heat pumps, have a method that words pretty good,
and its a subcool variation...you measure the hot gas discharge temps, and
normally, IIRC, its 125F above ambient temp and its charged the way they
In order to charge correctly, the tech needs to KNOW, and not guess, that
the evap and condensor coils are clean, and both fans are operational, and
at capacity...meaning, running correctly.
Provided that the duct is sized correctly, and there are no restrictions in
the duct that would alter the pressure and temp readings, he needs to know
the wet bulb temp, ambient temps, metering device type on the evap coil,
return air temp, suction line temp, and then run a quick couple of
calculations and if the superheat figure that is listed for that particular
unit is low, he needs to remove some refrigerant..if its high, add some.
Oh..and he cant tell in 5 minutes either...so if you have one come out, and
suddenly its cooling again, and hes not been in the house, hes used that
favorite method of hacks...beer can cold method....hes when hes normally got
the system overcharged, and the suction line starts to sweat like a pig, and
then, its cooling...let the temps rise about 15F and then you think you have
a problem again.
BTW, I didnt go into tons of detail on the subcool and superheat, as there
are about 3X ways I know of to check it, and each unit has the superheat
chart someplace on it...it wont have directions on how to check it, since
the tech installing, or working on the unit is supposed to know. It varies.
Some will argue this, but the basic principle is the same...you are looking
to see how much heat the unit is picking up in the evap coil basically in a
nutshell...since that is how an AC works...there is no such thing as "cold",
just lack of heat. An AC is nothing but a method to move heat. You move it
from inside your home, to the outside..the idea is to do it quickly, and
efficently. Just because its "working" does not mean its doing it was well
as it could, and most people find that after its done right, their bills
tend to drop, even if slightly, and the unit makes the home much more
And yes, I agree that there is not enough regulation in the industry to keep
morons, hacks and otherwise dangerous people like some that actually post in
here out of the trade. I dont mind telling you that StorminMoron...(SICOP)
is one. Hes a locksmith that tries to be a pro, and he holds no professional
licence, since its not required in his state...a shame.
That one thing...along with some owners that dont follow up, or train, is
what gives the industry a black eye...Mr. HVAC is Fun, AKA Dave, is another
one that would like you to think that those of us that tell it like it is,
and refuse to sugar coat things is what does...but hes proven unable to be
correct, or safe on most of his advice, and refuses to try to listen to
those that are proven to be professionals.....no matter if he does not agree
with our way of conveying thoughts...
If you have a tech that tells you...look, its screwed all to hell, here is
why, shows you and explains it to you and you understand and trust him,
there is no reason to have a guy that holds your hand and sugar coats the
fact that hes about to hit you up for $8900 for a unit that some of us can
put in for under $5000.
You'r correct that there are too many untrained guys that have the nerve
to work on HVAC systems. If a tech can't show you a superheat chart and
doesn't have a set of electronic thermometers to take readings he's not
likely to get the job done right. The old time hacks of chargeing to 30 over
ambient or beer can cold were never sound methods and are even worse with
higher effiency units. Not much has changed to increase effiency but the use
of larger coils indoor and out to move heat with lower head pressures and
remove humidity better with larger coil surfaces. To get the desirded
results the systems must be charged by a trained tech that knows and
understands what the hell is going. Even the lowest effiency system useing a
metering device subjected to a hack method of chargeing in many cases will
cool poorly, useing more electricity and in the worst cases slugging the
compressor valves with liquid.
I worked for a short time for a small HVAC company were several of their
"techs" had no clue as to the proper methods of chargeing a system. They
didn't know what a superheat chart was and had no clue as to how to charge
to subcool or which type systems used this method. They were easy to spot as
the only equipment used for evaluation were a set of gauges and a pocket
thermomoter used to measure the discharge temperature of the outdoor coil.
When on call I'd spend my weekends removeing refriderant from overcharged
systems, that were just serviced. Luckily this type company is the exception
to the rule and in most cases will not survive because money lost to
As to trying to dignose a cooling problem with the only know values being
the supply temperature, rough outdoor temp and a complaint of long run
cycles let me guess it's a high head causeing a high suction pressure or
normal if the latent load is high (humidity). Check the compressor to see if
there is water running off it from condensation, if so, could be improper
charge, dirty evap coil and or fan. All things that should have been noted
when it was serviced,
Maybe you should call a qualified, trained, licensed technician to come out
and check your air conditioner over, evaluate its operational performance,
and provide you with estimates for repairing any problems that are found.
He could probably tell more about it by looking at it and inspecting it than
we can over the internet.
Your AC is doing good..so you must need more insulation....
Many thing come in to play..
like how many people in the house...
but all in all if you are getting 60F out of the vents your AC is working good.
Today was a worst-case day for heat in Florida. High humidity, sunny,
90s. Your system could be running quite well.
Typical hoped-for differential would be 15 to 20 deg F between ambient
at the return and output from the vents. If your ducts are in a hot
attic, and the house is at 75 deg F, then 60 deg F at the vent is
Tip: Hang, permanently, one of those $10 indoor-outdoor digital
thermometers from Wal-Mart or Radio Shack by the most visible vent, with
the outdoor bulb immersed in the airflow in the vent. I have one
permanently installed in the kitchen, which lets me check performance
easily. Once you get to know how your system performs under different
outdoor conditions, you can check performance any time you like.
Now you're gonna get a lot of cranky advice from all the experts here,
about how A/C is too complicated for you to understand and you should
just pony up for a service call, but this is one test you can do
yourself that is cheap, easy, and impossible to misread.
When I had the home inspected by an inspection company, they did as you did.
He put an analog temp probe into a vent, into the return, and into the main
stack. He said it should be around a 20 degree difference between the air
going into the return and the a/c coming out. At the time, I was 25F
difference, and he said that indicates a problem. When checked yesterday,
it was around 20F. It was 80-81F at the return, and 60F coming out of the
vents. So I don't see how it could be operating so poorly. The thermostat
in my living room is what decides to turn the thing on and off based on the
setting I put in it. So if the fan/compressor cycle on/off based ont hat
(which they do just fine), and it's blowing cold air, where else can there
be a problem about it not cooling the house properly?
I guess the vents could be too small based on todays code, or not placed
properly. But the house in 23 years old, so it's not up to today's code, so
what can I suspect?
Or maybe some vents are blocked, I know at least once is in 1 room because
of poor placements. But I seem to get plenty of CFM out of the other vents.
But I don't know what it's supposed to be.
I'll most likely call my home warranty company and have it checked anyway.
Only costs me $45 for a service call.
It's not too complicated. It is more complicated than an indoor/outdoor
thermometer. They are called air conditioners, not air coolers for a
reason - your idea doesn't leave much allowance for latent heat. The simple
thermometer is good for a quick glance reference but is about as accurate as
trying to back up 4 feet using your odometer.
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