PTAC Unit

Overview

A PTAC (packaged terminal air conditioner) is a self-contained heating and cooling unit installed in a through-wall sleeve, typically in a hotel room, apartment, or office space. The entire refrigeration cycle, compressor, condenser coil, expansion device, and evaporator coil, is sealed within a single chassis that mounts in a window or wall opening. Indoor air passes over the evaporator coil, where refrigerant absorbs heat and cools the room. Hot, high-pressure refrigerant vapor flows outdoors through refrigerant lines to the condenser coil, where a fan rejects heat to outside air. An electric resistance heater provides winter warming. The unit is independent of any central HVAC system, allowing individual room temperature control without ductwork or a main plant.

PTACs dominate the hospitality industry and rental housing because they are cheap to install, require no ductwork modifications, and allow each room to be heated or cooled independently. However, they are noisier and less efficient than split-system air conditioners and consume more electricity per ton of cooling. They are being gradually displaced by mini-split heat pumps in high-end properties but remain standard in budget hotels and apartments.

How it works

The hermetic compressor, typically a 0.5–1.5 hp scroll or reciprocating unit, is driven by a single-phase AC motor. When the room temperature rises above the thermostat setpoint, a relay energizes the compressor motor. Low-pressure liquid refrigerant from the expansion device (not shown in the BOM; assumed internal) enters the Indoor Evaporator Coil at low temperature and pressure. As indoor air is blown across the coil by the indoor fan motor, the refrigerant evaporates and absorbs sensible heat, leaving the coil as a cool vapor. This cooling action removes thermal energy and latent moisture from the room.

The low-pressure refrigerant vapor exits the evaporator and flows into the compressor's inlet port. The compressor's pump stage increases the pressure to 15–25 bar and raises the temperature substantially (adiabatic compression). This high-temperature, high-pressure vapor is discharged to the outdoor Outdoor Condenser Coil, where a fan motor forces outside air across the coil. The hot refrigerant condenses into a high-pressure liquid, rejecting the absorbed indoor heat to the outdoors. The condensate from the evaporator drains through gravity or a pan drain to the outside.

In heating mode, an electric heating element (2–5 kW) is activated instead of (or in addition to) the compressor. The room fan circulates air across the hot heating coil, warming the space. No refrigerant cycle is involved; heat is generated directly via electrical resistance. This "heat pump switchover" design (cooling via compressor, heating via electric element) is simpler and more reliable than reverse-cycle heat pump operation.

Compressor and Refrigerant Circuit

The Hermetic Compressor is a sealed hermetic unit: motor and pump share a common oil sump, and the shell is welded permanently closed. Refrigerant circulates through the oil, lubricating bearings. The compressor discharge line is hot (often 80–100°C); the suction line is cool (−5 to +5°C). These lines are insulated and routed through the Wall Sleeve and Trim to minimize heat loss and condensation.

Modern PTACs use R-410A (high-pressure, non-ozone-depleting refrigerant, 1–2 kg charge) or the newer R-32 (lower pressure, slightly better efficiency). Some older units still operate on R-22, now being phased out. Service technicians must be EPA-certified to handle refrigerants.

Condenser and Evaporator

Both coils are aluminum fin-tube designs: copper tubes brazed into aluminum fins. The condenser is exposed to outdoor elements (rain, dust, salt spray) and often accumulates corrosion or debris; annual cleaning is recommended. The evaporator is indoors and typically cleaner but can collect mold spores if the drip pan stagnates. A clogged evaporator restricts airflow and reduces capacity.

Electrical and Control

PTACs are wired directly to a 120 V (15 A) or 240 V (20 A) wall outlet or hardwired circuit. A built-in thermostat and relay measures room temperature and controls compressor and fan motor operation. Most units have a mechanical rotary dial for temperature setpoint and separate switches for mode (Cool/Heat/Fan-Only/Off) and fan speed (Low/Med/High). Some newer models feature wireless remote controls and programmable setpoints.

Installation and Through-Wall Configuration

The Interior Chassis and Housing is mounted inside a wall sleeve, a galvanized steel frame that slides through a cut opening in the wall. The sleeve is typically 20–30 cm deep, allowing the outdoor condenser section to protrude beyond the exterior face. Interior and exterior trim collars cover the wall edges and are adjustable to fit various wall thicknesses. Foam gaskets around the perimeter seal air and moisture infiltration gaps.

Installation is rapid: cut a rectangular hole, slide the sleeve through, secure with bolts, caulk the exterior trim, and plug in the unit. No refrigerant work is required (pre-charged sealed system), making it a task for maintenance staff rather than licensed HVAC technicians.

Advantages and Limitations

Advantages: low capital cost; simple installation (no ductwork); independent room control; works in rental properties (no permanent modification); compact. Limitations: high operating cost per ton (EER 8–12 vs. 12–16 for central systems); noisy (compressor and condenser fan); requires exterior wall access (limits placement); poor humidity control; visible appearance; no fresh outside air delivery without separate equipment.

Energy and Maintenance

Annual maintenance includes cleaning the outdoor condenser coil (high-pressure water spray), changing or cleaning the indoor air filter (every 2–3 months), and checking drain pan and drain line for blockages. Refrigerant charge decay is rare in sealed systems but can occur if tubing develops micro-leaks; this manifests as reduced cooling capacity.

Modern code often requires PTACs in new construction to have a minimum EER of 9–11 and noise limits below 50 dB(A) indoor. Mini-split heat pumps (ductless systems) are increasingly preferred as replacements because they are quieter, more efficient, and capable of heating without electric resistance.