This is another video in my series where I’m trying to establish a troubleshooting
flow chart for air conditioning systems that don’t seem to be running right.
So, the customer tells you the inside air handler seems to be blowing air,
just not cold air. But, they also tell you the AC outside is running. So what could it be?
Let’s go through some checks to get you in a better place.
Without making this a long-drawn-out process, I will assume you have the basic
electrical troubleshooting skills and a multimeter with an amp clamp and some temperature probes and
get right to the flow chart I have created. And we’re going to assume this is a single-stage AC.
Two-stage and variable speed systems are similar to single-stage but different.
Fair warning: It’s really easy to get electrocuted troubleshooting.
If you don’t have the right skills for this, call a technician who does.
Also, I like to tell the customer that I will find and fix the first problem I see. Once I fix it,
I’ll run the system again to see if anything else in the sequence of operation is not running right.
It’s a nice caveat to mention so they don’t think you’re trying to rip them off.
Okay, the indoor air handler is blowing air. Albeit it room temperature air. And
you’re told the condenser outside is running. I always start by checking the filters to see
if they are clean - no matter where they are (Including in the attic if it’s there.
I’m usually not antsy to head into the attic on hot summer days, but sometimes it’s like a 4”
media filter at the furnace in the attic, and if it’s caked, that will solve a lot of problems.)
Because, a lot of times on a service call, you’ll get to the house and see a perfectly clean filter.
So, I like to acknowledge the customer in a positive way for changing their air filter
and remind them it’s the single most important thing they can do to keep their system clean
and running for many years. At the same time, I want to know when they changed it and how dirty
it was before replacing it yesterday. Because how many times have you gotten to the house,
and the customer says, “I just changed the filter yesterday.”
Anyways, heading outside, from first glance, are the condenser coils clean? Honestly, dirty filters
and dirty coils are related to about half of your problems with AC units that aren’t cooling enough.
If you find that the condenser fan is running, but the compressor at the bottom of the unit
is not running, click here to check out How I Troubleshoot an AC: Condenser Fan is Running,
but Compressor Isn’t (Insert link) But if the compressor is running,
make sure you have matching-sized evaporator and condensing coils. If you don’t, install
matching coils. Everything relies on a balance of refrigerant and airflow across these coils.
And its starts with the right size equipment. Do you have the right 300 to 400 cfms/ton of
air going across the coil? No? Check the return duct to make sure it’s sized right
and not crushed. Also, check the airflow chart in the book. It will give you details as to
where the dipswitches or speed taps need to be to achieve proper cfms of airflow.
If you do have proper airflow across the coil? Check to see if you have a TXV or a fixed
orifice metering device at the evaporator coil. Is it a fixed orifice? Is it the right size?
If it’s not, install the correct size orifice? Yes? The orifice is already the right size? Then,
is the superheat higher or lower than the required superheat for that setup?
It’s too high? Charge it up to specs. Is the superheat too low? Then you’ll need to remove
some charge to get it dialed in just right. Or was the metering device a TXV? Is it the
right size and designed for the same refrigerant in your system? Let it run for a few minutes. Your
gauges could be doing a myriad of things right now depending on whether the TXV is stuck open,
hunting, or partially stuck closed - so, let’s get into faulty TXVs in another video.
I’ll try to link it to the end of this video/blog so you can easily switch over to that in a minute.
Let’s check some of the basic fundamentals, though, before we start throwing more
refrigerant into the system. • Are the air filters clean
(are there more than one?) • Are the condenser coils clean?
• Is the evaporator coil clean? • Is the blower assembly clean?
• If it’s a condensing furnace, is the secondary heat exchanger clean?
• It might sound weird, but has the condenser fan blade been changed since the original
install? Is it still the right size, removing heat efficiently?
• Check the refrigerant charge. I have a video on How I Add Refrigerant to an AC System. But as a
reminder, measuring your subcool and superheat with your gauges and some temperature sensors
is the correct way to determine whether you have the right amount of refrigerant in the system.
• Is there a restriction in the refrigerant lines in the form of a kink somewhere in the lineset
that runs between the outdoor and indoor units? • Another restriction could be at the filter
drier. Is there more than a 2 to 3-degree difference between one side
of the liquid line filter drier and the other? • If the refrigerant charge is correct and you’re
still not getting sufficient cooling, check the size of the unit itself. Especially if there has
been any remodeling, add-ons, or major changes to the home. That affects the load on the house
and could mean that the system is too small now. • I’ve been to a lot of those massive pre-planned
communities that were all built like an assembly line. The HVAC contractor who
won the job for that huge project may have miscalculated the size it needed to be.
If the unit is not large enough to overcome the heat load put on the house, the system will
just run all day and never get the house cool. • Check the home’s insulation levels and keep it
in mind when determining your conclusion. • If there seems to be a problem with one
room not getting enough, then there is likely a problem with the duct system or its design.
o Maybe adding a larger duct to that south-facing room will deliver the right amount of air.
That might also mean enlarging the c-box and supply register in that room.
Usually not, though. o Are any of the ducts
crushed? Especially the return ducts. o Maybe the duct is in a poor spot on
the supply plenum, so it’s an afterthought for the air entering the supply plenum.
The air hitting the back of the supply plenum will always get the most advantageous air.
o Is the duct that is supplying that room attached to a tee-wye? Is the wye built correctly? Does it
split off at a 35° to 45° angle and not like a real “T’ at a sharp 90°. KD pipe with a hard
90 won’t allow the air to divert towards that duct. It will take the path of least resistance.
Make sure you have a good tee-wye connection. We often get to this point where it MUST BE THE
TXV! Check out my video on How I Diagnose a Bad TXV. There’s a lot to consider when going down
that road, but I promise I can get you through it. If this is your first time watching our channel,
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Thanks so much for watching, and we’ll see you on the next video.