AC Compressor Runs but Blowing Warm Air | 🚛🏡 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.

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 

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.

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.

pexels photo 11039667

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,   please click subscribe down here on the 
bottom right. And if you click the little   bell next to it, you’ll be notified 
of all of our videos as they come out.  Thanks so much for watching, and 
we’ll see you on the next video..

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