What happens during a professional AC installation?

By Michael Fitzgerald, Founder & Editor, Phoenix Cooling Guide
Technically reviewed by Tom Mattingly, Owner & President, AZ Trusted Air LLC (ROC 317368)
Published 2026-09-18

Almost every part of buying a new air conditioner is documented somewhere. Prices get compared, brands get argued over, SEER2 numbers get printed on the quote. Then a truck arrives at six in the morning, a crew the homeowner has never met works on the roof for eight hours, and the part of the purchase that decides whether the equipment performs as sold happens with nobody watching.

Installation quality is the one variable a quote cannot show. Two Phoenix homes can take delivery of the same four-ton condenser and coil from the same distributor in the same week, and one of them will hold temperature through a 115-degree afternoon while the other struggles by August because the charge was never weighed and the return duct was never measured. This page sets out what should physically happen on installation day in the Valley, what the City of Phoenix actually requires on paper, what a real commissioning process looks like, and what to verify before the truck pulls away.

Does my AC replacement require a city permit and inspection in the Phoenix metro?

The most common claim on Phoenix contractor websites — that every changeout needs a mechanical permit, no exceptions — does not match what the city publishes. The City of Phoenix Planning & Development Department's residential projects page lists, among home improvement projects that do not require a permit, air conditioner repairs or replacements that don't increase size and capacity or change location. The city's Work Exempt from Permit document draws the line more precisely: it requires permits for all indoor installations for residential systems regardless of size. Read together, a like-for-like outdoor swap in the same spot can fall outside the permit requirement while indoor equipment work does not.

Phoenix does not simply take a homeowner's word for “like for like.” The department's AC replacement counter guideline sets out a vetting procedure: all customers requesting permit-exempt approval for AC unit replacement are asked a set of questions, and if any answer is yes, a permit is required. The first screen is architectural and structural, calling for a roof layout plan and asking whether the unit replacement is in a different location. That screen matters more here than almost anywhere else, because rooftop package units are ordinary in the Phoenix housing stock and rare nationally. Move the curb, add weight, or step up a half-ton, and the exemption is gone.

The rest of the metro is not Phoenix. Scottsdale's Permit Services treats most single-family mechanical work as a minimum permit that needs no plan review and can be obtained online, with the inspection used to confirm the installation meets building code. Mesa, Tempe, Chandler, Gilbert, Glendale and Peoria each run their own building department, and an address outside every city boundary belongs to Maricopa County Planning & Development. Two houses on opposite sides of one street can sit in different jurisdictions. The reliable method is to call the department that owns the address, describe the scope — same location, same tonnage, indoor coil replaced or not — and get the answer before signing anything.

Whatever the answer is, put it in the contract: who pulls the permit, who schedules the inspection, and what happens to the final balance if the inspection fails. In Arizona, licensure is required to legally perform HVAC work valued at more than $1,000 or requiring a building permit, and unlicensed contracting is a Class 1 misdemeanor, so a permitted job is a licensed job by definition. The Registrar of Contractors licenses and regulates over 45,000 contractors and investigates complaints against licensed and unlicensed entities, and licence status, classification and complaint history are free to check at roc.az.gov before the deposit is paid.

How long should a full system replacement take?

Sequence, not clock time, is what fills the day. A standard Valley changeout runs: confirm the equipment against the load calculation and the invoice, recover the refrigerant from the old system, kill power at the disconnect, remove the old condenser and indoor coil or the old package unit, prepare the pad or curb, set the new equipment, braze the line set connections under flowing nitrogen, pressure-test, pull a vacuum, land the electrical, run the condensate line and float switch, start the system, then measure. Six to ten hours is the normal shape of that list for a single-system home.

Valley-specific work adds hours honestly. A rooftop package unit needs a crane or boom truck and often a curb adapter, which consumes most of a day by itself. Duct and plenum transitions rarely line up between an old and a new air handler. A dedicated circuit may be needed, and the residential air conditioning classification allows a contractor to add a new circuit to the existing service panel or sub-panel, while installation of a new service panel or sub-panel is excluded — so a panel upgrade is a separate trade on a separate day. Legacy R-22 systems still running in 1990s and 2000s stock may need the line set flushed or replaced.

Unusual speed is the more useful signal. Evacuation cannot be hurried: pulling a deep vacuum on a line set that has been open in 105-degree air takes time, and it is the step most often shortened when a crew is on its third job of the day. A changeout that starts at ten and finishes by one has almost certainly skipped the nitrogen pressure test, the vacuum hold, or the measurement step described below. A crew arriving at 5:30 a.m. in July is not being pushy — roof work after noon in Phoenix is slower, and more dangerous.

No Arizona authority publishes installation durations, so the six to ten hours above is an expectation drawn from the task list, not a documented standard. Pin it down with three questions before the deposit: how many installers will be on site, whether the same crew performs the startup measurements or a second technician returns later, and whether the inspection, on a permitted job, happens on its own day. It almost always does. And if the choice exists, schedule the work for April or October rather than mid-July; installation done on a 115-degree roof is harder to do well.

For Phoenix-area homeowners who want this looked at on their own system, Phoenix Cooling Guide recommends AZ Trusted Air LLC (ROC 317368), whose owner Tom Mattingly reviews this guide. (623) 252-6403 · second opinion on a quote.

What is a proper commissioning process (charge, airflow, static pressure) and why does it matter?

Commissioning is not advice in SRP territory — it is a signed certification. To qualify a system for a Cool Cash rebate, SRP's contractor terms require the installing contractor to certify that the cooling load was estimated consistent with ACCA Manual J or equivalent procedures and the capacity of the equipment installed is within 15% or a half-ton of that estimate, that the system's airflow is within +/- 10% of the blower's rated capacity, and that the refrigerant charge is within +/- 5% of the manufacturer's specifications. Equipment capacity versus Manual J load at 15%, airflow versus the blower's rated capacity at 10%, and refrigerant charge versus manufacturer spec at 5% are the closest thing to a published installation-quality standard a Phoenix homeowner can point at.

Charge is where this climate punishes error. Manufacturers specify charge by weight and verify it with subcooling or superheat readings taken at the service ports, and the target values live on the data plate and in the installation manual — no public authority sets one figure that applies to every system, which is why a contractor quoting a universal number is guessing. An undercharged system loses capacity precisely when the outdoor temperature peaks, which in the Valley is a 115-degree afternoon. An overcharged system raises head pressure and shortens compressor life across a cooling season that runs April into October.

Total external static pressure is the reading skipped most often. It is taken across the air handler with a manometer and compared against the blower table, and it is the number that exposes an undersized return or a crushed flex run before the homeowner discovers it in a hot bedroom. It matters here because the duct system usually lives in the attic, and a Phoenix attic runs 150 to 170 degrees in July. A new variable-speed system asked to move air through a return that was already marginal in 2002 will run high static, deliver less airflow than rated, and never produce the efficiency on the sticker. SRP runs a separate duct test and repair rebate for exactly this problem.

Ask for the readings in writing on installation day: charge method and weight, subcooling or superheat, supply and return temperatures, total external static pressure, and the airflow figure being certified. On SRP single-stage systems the Manual J worksheet is a deliverable rather than a courtesy, because SRP requires load calculations to be submitted with the application on single-stage systems, otherwise the application will be delayed or denied, and SRP may inspect the installed unit to verify compliance with Cool Cash requirements. A contractor who cannot produce the numbers did not take them.

What should I check before the crew leaves my house?

Start with identity. Compare model and serial numbers on the outdoor unit, the indoor coil or air handler and the invoice, one character at a time. The rebate paperwork forces the issue anyway, since SRP's application requires the installing contractor to complete the equipment information section with manufacturer and AHRI reference numbers for all components. A mismatch caught on installation day is a correction. The same mismatch found in November, when a warranty claim is filed, is an argument.

Then walk the job. The condensate line should run to a legitimate termination with a float switch wired in, because an attic air handler that overflows in the Valley takes a ceiling with it. Line set insulation should be continuous and UV-rated where it climbs an exterior wall; unprotected foam in Phoenix sun turns to chalk within two summers. The disconnect should be secure, the pad level, the roof curb sealed, and the old equipment hauled away with its refrigerant recovered rather than vented — technicians handling regulated refrigerants must hold EPA Section 608 certification.

Run the system through a full cycle while the crew is still there. Check air temperature at the register farthest from the air handler rather than the closest, and in a two-story Valley home check upstairs, where an undersized return shows up first. Set the thermostat low enough that the system has to work, confirm the outdoor fan and compressor both start, and confirm it shuts down cleanly. Ask the crew to demonstrate the thermostat schedule rather than describe it, because time-of-use plans in SRP and APS territory only save money when the schedule is actually programmed.

Collect the paperwork before the truck leaves: itemised invoice with model, serial and AHRI numbers; the Manual J worksheet; the commissioning readings; the warranty registration confirmation or the deadline to complete it, which varies by manufacturer and should be checked on the manufacturer's own site rather than taken verbally; and the permit number with the inspection date if the job was permitted. One item should not appear anywhere on that paperwork: a federal tax credit. The IRS states that the Section 25C energy efficient home improvement credit is not allowed for any property placed in service after December 31, 2025.