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Troubleshooting Guide — What to Do If Your PTAC Isn’t Heating or Cooling

Introduction — Mike Here: If Your PTAC Isn’t Heating or Cooling, Don’t Panic Yet

You walk into the room.
It’s hot. Really hot.
You crank the PTAC down to 65°F… and nothing happens. No cool air, no satisfying hum, maybe not even a fan.

Or worse — it’s winter, and instead of heat, you get cold air blowing in your face.

I’ve been there. And trust me:

Most PTAC problems are simple fixes you can do in minutes — no tools, no pros, no drama.

This troubleshooting guide is the most complete one you’ll ever read. Whether you’re a homeowner, landlord, Airbnb host, or managing a whole floor of hotel units, this will help you diagnose:

No cooling
Weak cooling
No heating
Weak heating
Unit won’t turn on
Leaking water
Musty smells
Frozen coils
Constant cycling
Loud operation

I’ve broken everything down into clear steps, explained why each issue happens, and how you can fix it fast — and when you should bring in a pro.

Let’s dig in.

1. PTAC Not Cooling at All (Dead Cooling Mode)

This is the most common complaint, and the good news is:
90% of the time, it’s easy to fix.

Let’s run through the list.

1.1 Check the Thermostat Mode (Cooling Must Be Selected)

I know — basic.
But you’d be surprised how many PTAC service calls happen because the unit is accidentally set to:

Fan
Heat
Vent
Automatic (that chose heating based on room temp)

Make sure the display shows:

COOL
AC
°F setting lower than room temp

1.2 Check the Power Cord Safety Plug (The GFCI)

Every PTAC has a built-in safety plug (GFCI). If it trips, the unit stops cooling instantly.

Reset it:

Find the “TEST” and “RESET” buttons.
Press RESET.
Restart the PTAC.

If it immediately trips again → electrical issue → call a pro.

1.3 Clean the Filter (Blocked Airflow = No Cooling)

A clogged filter kills cooling faster than anything else.

The EPA stresses the importance of clean HVAC filters for efficiency and performance:

If your PTAC isn’t cooling, clean the filter.

It takes 20–30 seconds and fixes more problems than you’d expect.

1.4 Frozen Evaporator Coil (Very Common)

If your PTAC runs but doesn’t cool, the indoor coil may be frozen.

Symptoms:

Weak airflow
Ice buildup
Water dripping
Cold air that suddenly stops

Fix:

Turn unit OFF.
Turn on FAN ONLY for 30–60 minutes.
Allow full thaw.
Clean filter.
Clean indoor coil.

The DOE explains that frozen coils come from low airflow or low refrigerant.

1.5 Dirty Evaporator Coil (One of the Biggest Causes)

Dust + humidity = coil “cement.”

This blocks heat transfer and stops cooling.

Fix:

Brush coil gently
Use coil cleaner
Vacuum carefully
Clean blower wheel

1.6 Vent Door Left Open (Warm Outside Air Infiltration)

PTACs have a vent door that brings in outside air.

If open, hot outdoor air comes straight inside.

Fix:

Close vent
Switch to “closed” position
Block slider if worn

Hotels close these permanently because vents cause more issues than they solve.

1.7 Refrigerant Leak (Least Common but Serious)

PTACs are sealed systems — refrigerant shouldn’t leak.

Symptoms:

Constant running
Lukewarm air
Frosted tubes
Hissing sound

The AHRI recommends professional repair for any refrigerant issue.

Fix:

Call a technician — do NOT DIY refrigerant work.

2. PTAC Cooling but Weak (Barely Any Cold Air)

If you’re getting some cooling but it’s weak, use this checklist.

2.1 Filter Partially Blocked

Even a little dust kills airflow.

2.2 Coil Dirty

You must clean both:

Indoor evaporator
Outdoor condenser

A clogged condenser coil can reduce efficiency by up to 30%, according to Energy.gov.
👉 Energy.gov.

2.3 Blower Wheel Dirty

If the wheel blades are covered in debris, airflow drops by 40–60%.

2.4 Incorrect Mode

Make sure it’s not in:

Dry
Auto
Low fan

Set fan to:

High
Cool mode

3. PTAC Not Heating at All

Heating problems fall into two categories:

Heat pump PTACs
Electric heat PTACs

Let’s check both.

3.1 Heat Pump PTAC Won’t Heat (Common in Winter)

Heat pumps stop heating below certain outdoor temps.

Standard heat pumps:

Stop at 40°F–45°F

Cold-climate heat pumps:

Work down to 20°F–25°F

Fix:

Switch to Emergency Heat / Electric Heat mode.

The DOE confirms heat pumps lose efficiency as outdoor temperatures drop.
DOE Heat pump system

3.2 Electric Heat Not Working

Electric heating uses a heat strip (similar to a giant toaster coil).

Symptoms:

Fan runs
Air is cold
No burning smell at startup (normal on first use)

Causes:

Failed heat kit
Loose wire
Bad relay
Faulty thermostat
Tripped safety sensor

Fix (DIY):

Reset breaker
Check safety plug
Clean filter
Remove obstruction blocking airflow

Fix (Pro):

Replace heat strip
Replace relay or control board
Test amperage draw

4. PTAC Only Blows Room-Temperature Air

If your PTAC runs but air isn’t cold OR hot, check these.

4.1 Unit in “Fan Only” Mode

No heating or cooling happens in FAN mode.

4.2 Compressor Not Engaging

Symptoms:

Fan runs
No humming
No click
No temperature change

Often caused by:

Bad capacitor
Failed compressor
Faulty control board

Call a pro for capacitor or compressor repair.
ASHRAE recommends professional repair for sealed-system issues.
👉 ASHRAE technical resources

5. PTAC Won’t Turn On

This is simpler than most people think.

5.1 Safety Plug Tripped (Most Common)

Reset GFCI on power cord.

5.2 Wall Outlet Dead

Check breaker panel.

5.3 Internal Fuse Blown

Requires removal of PTAC chassis.

5.4 Thermostat Failure

If your model uses an external wall thermostat, that could be the issue.

6. PTAC Leaking Water Indoors

This is ALWAYS a drain problem.

The EPA identifies poor drainage as a primary cause of HVAC moisture issues.

6.1 Drain Pan Clogged

Dust + water = slime.

Fix:

Remove PTAC → clean drain pan thoroughly.

6.2 Drain Holes Blocked

Clear holes with:

Pipe cleaner
Compressed air

6.3 Wall Sleeve Not Tilted

Sleeve must tilt ¼ inch downward toward outside.

7. PTAC Making Loud or Strange Noises

Common noises include:

Rattling
Grinding
Clicking
Screeching

Each noise points to a specific issue.

7.1 Rattling

Loose screws or loose blower wheel.

7.2 Grinding

Blower motor bearings failing.

7.3 Clicking

Thermostat relays — normal.

7.4 Screeching

Fan motor failing — replace ASAP.

8. PTAC Keeps Freezing Up

Frozen coils are incredibly common.

Causes:

Dirty filter
Dirty coil
Low refrigerant
Blocked airflow
Running AC in very cold outdoor temps

9. PTAC Smells Musty or Moldy

This is usually:

Dirty evaporator coil
Dirty drain pan
Standing water
Clogged drain

The EPA specifically warns about mold in HVAC condensation pans.

Fix:

Clean coil
Clean pan
Add antimicrobial pads
Run fan-only mode occasionally

10. PTAC Short Cycling (Turns On and Off Quickly)

Causes include:

Dirty coil
Overheating compressor
Bad thermostat sensor
Cold air blowing onto thermostat

Fix the airflow issues first — 80% of short cycling is dirt-related.

11. PTAC Troubleshooting Quick-Reference Chart

Problem	Most Likely Cause	Fix
No cooling	Dirty filter	Clean filter
Weak cooling	Dirty coils	Clean coils
Frozen coil	Low airflow	Thaw + clean
No heating (heat pump)	Low outdoor temp	Switch to electric heat
No heating (electric)	Burnt heat strip	Replace strip
Leaking water	Clogged drain	Clear drain pan
Loud noises	Loose blower or motor issue	Tighten/replace
Won’t turn on	Safety plug tripped	Reset GFCI
Musty smell	Mold in pan/coil	Clean + sanitize