Installation Pitfalls to Avoid with Horizontal Package AC Units — Tony’s Field Checklist
Introduction
If there’s one thing I’ve learned after 20+ years in the HVAC field, it’s this — a good air conditioner can still run terribly if it’s installed wrong.
The Goodman 2.5-Ton 13.4 SEER2 Self-Contained Horizontal Package AC Unit is one of the easiest systems to install on paper. It’s all-in-one, factory-charged, and built for quick connections. But that simplicity tricks some folks — both DIYers and contractors — into cutting corners that cost efficiency, lifespan, and even warranty coverage.
Whether you’re doing it yourself or hiring a crew, it pays to know what can go wrong before the wrenches come out.
In this guide, I’ll walk you through:
✅ The most common horizontal package AC install mistakes I’ve seen in the field
✅ Why they happen, what they cause, and how to prevent them
✅ Tony’s personal install checklist that ensures quiet, efficient operation every time
This isn’t theory — this is real-world, boots-on-the-ground advice that’ll save you hundreds (and maybe your system).
1. The Ground Game — Bad Pad Placement
Let’s start at the bottom — literally.
I’ve lost count of how many “new installs” I’ve been called to fix because the unit wasn’t leveled.
It might not sound like a big deal, but trust me — it’s a silent killer for compressors.
What Goes Wrong
-
The concrete pad or composite base isn’t level (off more than ½ inch)
-
Ground under the pad settles unevenly.
-
The installer forgot vibration isolators.
What Happens Next
-
Compressor oil shifts unevenly → poor lubrication → early failure
-
Drainage issues cause pooling and rust under the cabinet.
-
Fan imbalance increases vibration and noise.
Tony’s Fix
Always:
-
Use a 4-foot level on the pad in two directions.
-
Add rubber anti-vibration feet under each corner.
-
Compact the soil or gravel base before placing the pad
“If your pad rocks, your system’s clock is ticking.”
(Energy.gov – Outdoor Unit Installation Best Practices)
2. Not Checking Duct Compatibility
The Goodman horizontal package is designed for flexibility — side or end discharge, supply and return on either side.
But I’ve seen installers mismatch duct size or fail to seal joints properly, and it kills airflow.
Common Mistakes
-
Reusing undersized ducts from a smaller unit
-
Skipping mastic and foil tape (using duct tape, which fails fast)
-
Not insulating the ducts in hot attics or crawlspaces
Consequences
-
Hot and cold spots
-
Reduced SEER2 performance by up to 20%
-
The compressor is overworking to meet temperature calls.
Tony’s Rule of Thumb
For a 2.5-ton system, ducts should move 1,000 CFM total.
That’s about 400 CFM per ton, or:
-
16-inch main supply duct minimum
-
14-inch return duct minimum
Seal every seam with UL-181 mastic — not fabric tape.
(Energy Star – Duct Sealing & Efficiency)
3. Skipping the Electrical Safety Check
Electrical setup is where many DIY installs go sideways.
Horizontal packages are all-in-one, but they still need a dedicated 240V circuit, a disconnect, and grounding that meets code.
Common Mistakes
-
Using old wiring that’s undersized for the amperage
-
No weatherproof disconnect switch nearby
-
Forgetting to torque terminals to spec
Why It Matters
Loose terminals create arcing — a silent heat buildup that can fry your contactor or compressor in months.
And skipping the disconnect? That’s a code violation and a serious safety hazard for anyone servicing the unit.
Tony’s Tip
-
Always match breaker and wire size to the unit’s MCA (Minimum Circuit Ampacity) label.
-
Goodman’s 2.5-ton unit typically calls for 30–35 amps, 10 AWG copper wire, and a fused disconnect.
-
Double-check the voltage before energizing.
(NFPA 70 – National Electrical Code (NEC))
4. Forgetting the Drain Line Details
Condensate drainage seems simple until it isn’t. I’ve seen beautiful installs with puddles forming under the unit two weeks later.
Mistakes I See All the Time
-
No slope on the drain line
-
Using flexible tubing instead of PVC
-
Missing secondary drain pan (in rooftop installs)
-
No safety float switch
Result
Standing water, mold, corrosion, and — my favorite — “the mystery leak” homeowners can’t find.
Tony’s Fix
-
Slope the drain line at least ¼ inch per foot.
-
Use 3/4-inch PVC with a cleanout trap.
-
Add a condensate safety switch — a $25 part that prevents $2,500 ceiling repairs.
(Energy.gov – Condensate Drainage Guidance)
5. Poor Duct Transitions and Air Leaks
If your supply or return openings don’t match the unit perfectly, you’ll need a transition — and if that’s sloppy, you’ll lose airflow and efficiency.
Typical DIY Mistakes
-
Gaps between the duct collar and the cabinet
-
Screws poking into the airflow path
-
No weather gasket or insulation wrap
Fix
Use sheet metal transitions with:
-
Foil-faced insulation wrap
-
Butyl tape instead of standard foil tape for outdoor joints
-
One-inch weather gasket around duct openings
Airtight ducts = quiet, efficient airflow.
6. Wrong Thermostat Wiring
It sounds simple — just connect the wires. But one wrong jumper or loose terminal can make your system short-cycle, freeze up, or never cool properly.
Typical Wiring Errors
-
Reversing “Y” (compressor) and “G” (fan)
-
No jumper between “R” and “Rc” on single-transformer systems
-
Old mercury thermostat reused without compatibility
Tony’s Golden Rule
When in doubt, label every wire before disconnecting the old unit.
Then confirm against Goodman’s factory wiring diagram inside the access panel.
If upgrading to a smart thermostat, check that it supports 24V single-stage cooling — not all do out of the box.
(Energy Star – Smart Thermostat Compatibility)
7. Blocking Airflow Around the Unit
This one drives me nuts — people try to “hide” their outdoor unit behind fences or bushes. I get it, nobody wants to stare at a metal box.
But you’re strangling it when you do that.
Why It’s a Problem
-
Restricts condenser airflow
-
Raises internal pressure → higher energy use
-
Causes premature compressor wear
Clearance Requirements
Goodman recommends:
-
24 inches on all sides
-
60 inches overhead
-
No shrubs or fencing that restricts discharge airflow
“If you can’t easily walk around it, neither can the air.”
(Energy.gov – Outdoor AC Clearance Requirements)
8. Skipping the Seal Test
After everything’s hooked up, you can’t just flip the switch and hope for the best.
You need to test for air leaks, vibration, and condensate flow before signing off.
Tony’s 10-Minute Test
-
Turn on cooling mode.
-
Check for steady compressor hum — no chattering or buzzing.
-
Verify suction and discharge airflow match direction arrows.
-
Listen for air leaks at duct joints.
-
Confirm condensate line dripping freely.
-
Check static pressure with a manometer (0.3–0.5 in. w.c. typical).
If you hear whistling, thumping, or rattling, stop — something’s not sealed right.
9. Ignoring Local Codes and Permits
I know — pulling a permit sounds like a hassle. But skipping it is a quick way to void warranties or fail resale inspections.
Why Permits Matter
-
Ensures your install meets mechanical and electrical codes
-
Protects warranty validity
-
Prevents liability issues if something goes wrong
Average cost? $75–$250.
Average fine for skipping it? Way higher.
10. Not Registering the Warranty
Goodman gives you one of the best warranties in the business — 10-year parts coverage — but only if you register within 60 days of install.
I’ve had customers call about a failed capacitor two years in, only to find out they never registered. That’s an expensive $150 mistake.
Tony’s Rule
As soon as you get your install paperwork, go to:
And fill out the form.
Save the confirmation email with your invoice.
11. Forgetting About Drain Pan or Roof Flashing
For rooftop installs, one missed detail can ruin a roof — and I’ve seen it happen.
Pitfalls
-
No roof curb flashing.
-
Drain pan not insulated.
-
Leaking condensate is soaking insulation under the roof membrane
Tony’s Pro Setup
-
Always use a factory roof curb with integrated flashing.
-
Add pan insulation wrap to prevent sweating.
-
Test water drainage before final sealing
12. Overlooking Vibration Control
Even a properly mounted horizontal package can create low-frequency hum that travels through walls or ducts.
Fix
-
Use vibration isolation pads under all four corners.
-
Don’t mount directly on wood or metal platforms.
-
Add flexible duct connectors to decouple vibration
Noise is energy — eliminate it at the source.
13. Neglecting Post-Install Maintenance
After the system’s in, it’s not “set and forget.”
Even the best installation needs its first checkup within 6 months.
Why
-
Filter clogging in the first season can restrict airflow.
-
Duct insulation can loosen and cause condensation.
-
Fasteners settle and may need retightening.
Tony’s Simple Schedule
-
3 months: Change filter
-
6 months: Check drain & duct seals
-
12 months: Full professional tune-up
14. Tony’s Ultimate Field Checklist
If you only remember one section, make it this one.
Here’s my personal field checklist for every Goodman horizontal package install — the same one I use with my techs.
Before Install
✅ Verify pad location and clearance
✅ Check voltage and breaker rating
✅ Inspect duct sizing and insulation
✅ Review thermostat compatibility
✅ Pull necessary permits
During Install
✅ Level and secure pad
✅ Connect ductwork with a gasket seal
✅ Wire per factory diagram
✅ Install fused disconnect and grounding
✅ Slope and test condensate drain
After Install
✅ Verify airflow direction
✅ Test amp draw and voltage
✅ Check refrigerant pressures (if applicable)
✅ Listen for vibration or rattling
✅ Confirm drainage flow
✅ Register warranty online
I don’t leave a site until every box is checked — and neither should you.
15. Final Thoughts — Do It Once, Do It Right
Horizontal package systems like Goodman’s are built to make your life easier — but “easy” doesn’t mean careless.
Every shortcut taken during installation steals efficiency, shortens equipment life, and chips away at your comfort.
If you treat the install like a long-term investment, you’ll get:
-
Lower energy bills
-
Quieter operation
-
Better humidity control
-
A full decade of trouble-free performance
Remember: the install is 50% of the system’s performance.
So do it once — do it right — and enjoy the kind of comfort that only comes from a job done by the book.
Know about the warranty and long term value in the next blog.
