Went on a no cool yesterday on a new install. Homeowner said system
worked for about a week and then stopped cooling. He said that there
was a noticeable difference in the amount of air coming from the
supply's, said that it is a lot less. Took amp and volt draw on blower
motor, had 5.4 amps and 120V. System is 3 tons at 1200cfm. Went in
attic and looked for kinked ducts, etc, none found.
Made sure speed taps were on correct spades. Took cover off of A coil
and looked for obstructions, none found. Touched side of motor and
hello howdy was it hot. I know that is not right so I am going to
replace the motor on Monday. How can you tell if the motor is putting
out the correct CFM at the air handler?
One oddball thing I did find is that the return static pressure is
1.0. The return duct is sized properly but when I went in the attic I
could hear the air rushing through it about two feet after the filter
grill. The noise is in one spot only, not the entire duct. Before the
install the duct was doing this and it was routed so that it was
pinched off in two places. Had the installers re-route it and it's
still making this noise. Also, the static pressure on it was 1.0
before they re-routed it. I thought it was being caused by the duct
being pinched off but I guess not. If I run the system with the blower
door off the static drops to 2.5, however, the airflow in the house
stays the same.
I thought about that but I did not have anything on the truck to seal
the duct back up if I took it off. You would think that the installers
would have noticed this when they re-routed it. When I go back monday
I am bringing some panduits and mastic with me.
Who installed it? Also, system make and model, and motor part number
especially, would be useful to know here.
Rated, not measured on site, I presume, from reading below.
Therefore, irrelevant in this context.
Why would they move by themselves after one week?
Measure it. :-)
Use an anemometer and multiply face velocity by duct pening face area,
to get flow rate. Don't forget to convert square inches to square
I'm surprised you asked that question, though.
Check current draw against motor specs.
Measure blower speed with tachometer.
Or count fins on blower wheel, use variable strobe/timing light,
adjusr for stationary pattern, record flashes per second and do the
If the blower was runnung backwards, or was set to the wrong speed,
either someone tampered with the wiring, or it wouldn't have worked
for the first week.
Hot motor case + low speed = fried motor (factory defect).
It's under warranty. Just replace the motor.
You ARE factory authorized, no? :-)
Also, if it's a homeowner self-install, the warranty may be void
These questions are getting ridiculous.
No wonder so many flame wars ensue in this NG.
In my opinion, you don't know what you're doing,
and you are "moonlighting". If so, that's illegal
So I thought this group was for professionals, not homeowners to ask
hvac questions? Not moonlighting, not doing side jobs, and yes, in a
lot of instances I do not have a fucking clue. I will have been doing
this trade for a whopping two years in September. What skill level did
you have at that point? Most of you in here have a skill level that I
can only hope to attain one day, as in you've forgotten more about
hvac than I'll probably ever learn. If I ask for help in here it's
because I want to learn to do this stuff right. So in that vain, you
can either help or not, but please, no need to be a smartass. Fwiw, if
I said the name of the company I work for, everyone in here would know
it instantly. They thought enough of my skill level that they promoted
me to a senior tech this year. I must say that when they did, I'm
thinking to myself, you've got to be fucking kidding. I have a long
way to go before my skills are at that level. But hey, I took the
extra money and am stepping up to the plate. I am pretty damn good for
only doing this for two years now though, just not that damn good.
Hang in there, Al.
Don't be afraid to ask for help in here.
Refresh the post for me.
Is this the one you're trying to determine the air flow for?
Run the furnace for 10 minutes on cooling speed. Make sure the humidifier
bypass is closed, if it has one.
Measure the return air temp, then the plenum temp a few feet from the top
of the plenum so as not to register any radiant heat. This will give you
you're delta T.
Determine the output from the rateing plate (NOT the input), and multiply
the delta T by 1.08, then divide the output by that number. That will give
you your CFM.
If it's low, remove the blower door and measure CFM again. If it increases
sunstantially, the restriction is in the return air side.
Hope this helps.
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