ULTIMATE TROUBLESHOOTING FLOWCHART 
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.
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