HVAC/R Systems Installation: Packaged Units, Split Systems, Heat Pumps, and Remote Evaporators

5.2.1 Identify the basic components of a self-contained air conditioning unit

A self-contained air conditioning unit is an air conditioner where the major refrigeration components are housed in one factory-built package. You’ll see these as window units, portable units, and many packaged terminal air conditioners (PTACs) used in hotels. The reason these units matter in installation work is that they hide much of the refrigeration circuit inside a sealed cabinet—so your job is often more about correct placement, electrical supply, airflow, condensate handling, and basic diagnostics than about field-fabricating refrigerant piping.

What “self-contained” really means (and why it matters)

In a split system, the evaporator is indoors and the condenser is outdoors, connected by refrigerant lines you install in the field. In a self-contained unit, the manufacturer has already assembled the refrigeration circuit and typically factory-charged it. That reduces the chance of installation-caused refrigerant leaks—but it increases the importance of airflow management and heat rejection. If you install a window unit in a tight sleeve with poor outdoor clearance, for example, the condenser cannot reject heat properly and the unit will perform poorly even if the refrigeration circuit is perfect.

The basic refrigeration circuit components (the “four main parts”)

Most air conditioners—self-contained or not—are built around the vapor-compression refrigeration cycle:

• Compressor: The compressor is the pump that moves refrigerant through the system and raises its pressure/temperature so it can reject heat at the condenser. If the compressor cannot start (electrical issue, failed capacitor, locked rotor), the whole cooling process stops.
• Condenser coil: The condenser rejects heat to the outside air. In a window unit, the condenser is on the “outdoor” side of the chassis.
• Metering device: The metering device (capillary tube, fixed orifice, or TXV depending on design) creates a pressure drop and meters refrigerant into the evaporator. This is what enables the evaporator to be cold enough to absorb indoor heat.
• Evaporator coil: The evaporator absorbs heat from indoor air. Moisture in the air often condenses on the cold coil—so condensate management is part of correct installation.

A helpful way to remember the roles is: compress (pump) → condense (reject heat) → meter (drop pressure) → evaporate (absorb heat).

Air-moving and heat-transfer components

Self-contained units also include components that make heat exchange possible in real spaces:

• Indoor (evaporator) fan/blower: Moves room air across the evaporator coil. Low airflow can cause coil freeze-up and poor dehumidification.
• Outdoor (condenser) fan: Moves outside air across the condenser coil. Blocked condenser airflow causes high head pressure, overheating, and reduced capacity.
• Air filters: Protect the evaporator coil from dust. A clogged filter reduces airflow and can lead to icing and compressor stress.
• Louvers and dampers: Direct airflow; some units have a fresh-air damper to mix in outdoor air. If left open unintentionally, it can add large heat and moisture loads.

Controls and electrical components you should recognize

Even though the refrigeration circuit may be sealed, self-contained units still rely on serviceable electrical/control parts:

• Thermostat/temperature sensor: Senses room temperature and cycles the compressor.
• Control board (or mechanical selector switch): Coordinates modes and fan speeds.
• Run capacitor (and sometimes start capacitor/relay): Helps motors start and run efficiently.
• Overload protection: Protects the compressor from overheating/overcurrent.
• Fan motor(s): Many window units use a single motor with two fan wheels (indoor blower and outdoor prop fan).

Condensate management (often the installation “gotcha”)

As warm humid indoor air contacts a cold evaporator, water condenses and must go somewhere. Self-contained units typically use one of these strategies:

• Drain pan and gravity drain (common in PTAC sleeves)
• Slinger ring on the condenser fan to splash water onto the condenser coil (improves heat rejection and evaporates water). A common mistake is assuming visible water is always a “leak”—some designs intentionally retain and sling condensate.

Correct installation usually requires:

• Proper unit tilt (for window units) so water drains to the intended side
• Clear drain passages (no packing foam left in place)
• Confirming the drain route won’t damage building materials

Example: Diagnosing poor cooling after installing a window unit

If a newly installed unit “runs but doesn’t cool,” don’t jump to “low refrigerant.” Start with what installation affects most:

1. Outdoor airflow: Is the condenser side blocked by a screen, fence, or tight enclosure?
2. Indoor airflow: Is the filter installed and clean? Are the louvers open?
3. Unit seating and tilt: Is it level when it should be slightly tilted outward? Is water draining correctly?
4. Electrical supply: Is voltage correct under load? Are extension cords being used (often not recommended by manufacturers)?

Exam Focus

• Typical question patterns:
  • Label the refrigeration cycle components on a diagram of a window/PTAC unit.
  • Explain what happens to heat at the evaporator vs. condenser.
  • Identify which components are likely field-serviceable (filter, capacitors, controls) vs. sealed (refrigerant circuit).
• Common mistakes:
  • Confusing the evaporator and condenser locations in a window unit (indoor side is evaporator; outdoor side is condenser).
  • Assuming any condensate presence indicates a failure—many units intentionally manage water.
  • Blaming refrigerant charge for problems actually caused by blocked airflow.

5.2.2 Identify and install a central air conditioning system

A central air conditioning system (commonly a split system) cools an entire building (or a major zone) using an outdoor condensing unit and an indoor evaporator coil connected by refrigerant piping. It matters because most residential/light commercial cooling is installed this way, and installation quality strongly affects performance, reliability, and lifespan.

System identification: what pieces make up “central AC”

A typical split central AC includes:

• Outdoor condensing unit: Contains the compressor, condenser coil, condenser fan, and often service valves.
• Indoor evaporator coil: Often mounted in a plenum above a gas furnace or inside an air handler.
• Air handler or furnace blower: Provides airflow across the evaporator coil and through ductwork.
• Metering device: Often a TXV (thermostatic expansion valve) or fixed orifice/piston, typically at the indoor coil.
• Line set: Two copper lines:
  • Suction (vapor) line: Larger, insulated, cool to the touch during operation.
  • Liquid line: Smaller, usually uninsulated (insulation depends on application/manufacturer).
• Condensate drain system: Drain pan, trap (where required), drain line, and sometimes a condensate pump.
• Controls: Thermostat, indoor/outdoor control wiring, contactor, and safety switches.

A useful comparison:

How the system works (step-by-step, in real building terms)

1. The thermostat calls for cooling. The indoor blower runs and the outdoor unit starts.
2. Indoor air passes over the cold evaporator coil. Heat moves from air to refrigerant; moisture may condense and drain away.
3. The compressor moves refrigerant to the outdoor condenser. The refrigerant is now hot and high pressure.
4. Outdoor air passes over the condenser coil, carrying heat away. The refrigerant condenses back toward a liquid state.
5. Liquid refrigerant travels back through the liquid line to the metering device, where pressure drops and the cycle repeats.

If any part of this chain is installed incorrectly—restricted airflow, kinked line set, moisture left in lines, wrong electrical wiring—the “refrigeration physics” still applies, but performance and reliability suffer.

Installation: the essential workflow (what you’re trying to accomplish)

Central AC installation is mostly about ensuring four things:

1. Correct airflow across the indoor coil
2. Correct refrigerant piping practices (clean, dry, leak-free)
3. Correct electrical and controls wiring
4. Correct condensate drainage

Below is what that looks like in practical steps.

Locating and setting equipment

• Place the outdoor unit on a stable, level base with adequate clearance for airflow and service access (per manufacturer).
• Ensure the indoor coil is oriented correctly (many coils are directional) and sealed to the plenum/ducts to prevent air bypass.

Common error: installing an oversized coil cabinet or leaving gaps—air takes the path of least resistance and may bypass the coil, reducing cooling and dehumidification.

Refrigerant line set installation (craftsmanship + contamination control)

Your goal is a sealed system that is leak-free and dry inside.

• Use proper tube support and avoid kinks.
• Insulate the suction line continuously to prevent heat gain and condensation.
• Use correct joining method (often brazing). A key best practice is flowing dry nitrogen while brazing to reduce oxidation scale inside copper tubing (oxidation can clog metering devices).
• Pressure test (commonly with nitrogen) to confirm no leaks—follow manufacturer guidance for test pressure.
• Evacuate with a vacuum pump to remove air and moisture. Moisture is a major enemy: it can form ice at the metering device and can react chemically with refrigerant/oil.

Condensate drain installation

Because the evaporator removes moisture, you must route water safely:

• Slope the drain line properly so it drains by gravity.
• Where a trap is required (common when the coil is on the negative pressure side of the blower), install it correctly so air doesn’t get sucked through the drain and prevent draining.

Common error: no trap where needed—resulting in water overflow and building damage.

Electrical and controls

• Provide correct disconnecting means and overcurrent protection as required by applicable electrical codes and manufacturer instructions.
• Wire the contactor, compressor, fan motor, and low-voltage controls correctly.
• Confirm thermostat wiring matches the system type (cool-only vs. heat pump uses different terminals and logic).

Commissioning: proving the system works after installation

Good installers don’t stop at “it turns on.” They verify operation:

• Airflow: confirm filter installed, blower speed set correctly, ducts open.
• Temperature split (general performance indicator): supply air should typically be cooler than return air during cooling; exact values depend on conditions.
• Refrigerant charge verification: many systems require checking superheat (often for fixed-orifice systems) or subcooling (often for TXV systems), using manufacturer targets.

Definitions you should be able to use:

• Superheat is how much the suction vapor is heated above its saturation temperature at suction pressure:

$\text{Superheat} = T_{\text{suction line}} - T_{\text{sat at suction pressure}}$

• Subcooling is how much the liquid is cooled below saturation temperature at liquid pressure:

$\text{Subcooling} = T_{\text{sat at liquid pressure}} - T_{\text{liquid line}}$

Worked example (conceptual): calculating superheat

You measure suction pressure and determine saturation temperature is $40\,^{\circ}\text{F}$. You clamp a thermometer on the suction line and read $55\,^{\circ}\text{F}$.

$\text{Superheat} = 55\,^{\circ}\text{F} - 40\,^{\circ}\text{F} = 15\,^{\circ}\text{F}$

That number is then compared to the manufacturer’s required target for the conditions and metering device type.

Exam Focus

• Typical question patterns:
  • Identify each major component in a split central AC and describe its function.
  • Put installation steps in correct order (set equipment, run line set, leak test, evacuate, release/charge, commission).
  • Interpret a simple scenario (poor drainage, iced coil, noisy outdoor unit) and link it to installation faults.
• Common mistakes:
  • Treating evacuation as optional—air/moisture left in the system can cause major performance and reliability issues.
  • Mixing up which line is insulated (typically suction line) and why.
  • Forgetting condensate management details (trap/slope/secondary drain where required), leading to water damage.

5.2.3 Identify and install an air-to-air heat pump

An air-to-air heat pump is an HVAC system that can provide both cooling and heating by moving heat between indoor air and outdoor air. In cooling mode it behaves like an air conditioner; in heating mode it reverses direction and brings outdoor heat indoors. It matters because installation mistakes can show up as both cooling problems and heating problems—and heat pumps add extra components (reversing valve, defrost system) that you must understand.

How a heat pump heats (the key idea)

Even cold outdoor air contains heat energy. A heat pump uses refrigerant to absorb heat outside (at the outdoor coil acting as an evaporator) and release it inside (at the indoor coil acting as a condenser). The system doesn’t “make heat” like electric resistance heat—it moves heat.

What makes a heat pump different from straight AC

Most components are similar to central AC, but heat pumps add or emphasize:

• Reversing valve: A directional valve that changes refrigerant flow so the indoor and outdoor coils swap roles between heating and cooling.
• Defrost control system: In heating mode, the outdoor coil can frost up because it’s cold. The unit periodically runs a defrost cycle to melt frost.
• Auxiliary (backup) heat: Often electric heat strips (or a furnace in dual-fuel systems). Aux heat engages when outdoor conditions reduce heat pump capacity or during defrost to prevent cold air delivery.
• Outdoor metering device(s) / check valves: Many designs meter refrigerant appropriately in both directions.

Modes of operation (what each coil is doing)

• Cooling mode:

  • Indoor coil = evaporator (absorbs indoor heat)
  • Outdoor coil = condenser (rejects heat outside)

• Heating mode:

  • Outdoor coil = evaporator (absorbs outdoor heat)
  • Indoor coil = condenser (releases heat indoors)

A common misconception is “the outdoor unit always rejects heat.” In heating mode, the outdoor unit is collecting heat, which is why frost is possible.

Installation considerations unique to heat pumps

Thermostat and control wiring

Heat pump thermostats typically use different terminal logic (for example, a call that energizes the reversing valve in one mode, plus staging for auxiliary heat). Correct wiring matters because a single swapped wire can cause:

• the unit to cool when it should heat
• auxiliary heat to run constantly (high energy use)
• defrost problems

Because terminal conventions can vary by manufacturer and system type, the safest practice is to follow the wiring diagram and setup instructions for the specific equipment.

Outdoor unit placement and airflow

Heat pumps run in winter when snow, ice, and low ambient temperatures exist. Installation should consider:

• Elevation of the outdoor unit above expected snow accumulation
• Drainage for defrost meltwater (it must not refreeze into a block that damages the fan or coils)
• Clearances to prevent recirculation of cold discharge air

Refrigerant piping and commissioning

The same best practices apply as central AC (clean brazing, nitrogen purge, leak test, evacuation). Commissioning includes verifying correct operation in both modes:

• Confirm reversing valve shifts properly
• Confirm indoor airflow is correct (heat pumps are sensitive to airflow)
• Confirm defrost initiates and terminates properly (per control strategy)

Example: Understanding defrost in the field

In heating mode, the outdoor coil is cold and below the dew point of outdoor air, so moisture condenses and can freeze on the coil. Frost blocks airflow, reducing the unit’s ability to absorb heat.

Defrost temporarily switches the system into a cooling-like condition so hot refrigerant warms the outdoor coil and melts frost. During this period, many systems energize auxiliary heat so occupants don’t feel a blast of cool air.

Common mistake: interpreting defrost steam/water as “the unit is failing.” Some vapor and water during defrost is normal.

Exam Focus

• Typical question patterns:
  • Identify the reversing valve and explain what it does.
  • Describe what happens to indoor/outdoor coils in heating vs. cooling.
  • Troubleshoot a symptom like “blows cool air in heat mode” by relating it to reversing valve/control wiring/aux heat.
• Common mistakes:
  • Assuming the heat pump cannot provide heat when it’s cold outside (capacity drops, but it still moves heat until limits are reached).
  • Misunderstanding defrost operation and mislabeling normal behavior as a fault.
  • Wiring thermostat terminals as if it were a cool-only system, causing incorrect staging or mode selection.

5.2.4 Identify and install a refrigeration condensing unit with a remote evaporator

A refrigeration condensing unit with a remote evaporator is a common commercial refrigeration arrangement (for example, walk-in coolers/freezers). The condensing unit (compressor + condenser) is located in one place—often outdoors or on a roof—while the evaporator is located remotely inside the refrigerated space. They are connected by field-installed refrigerant piping and controls.

This matters because, compared with comfort cooling, refrigeration systems often run longer hours, operate at different temperatures, and are more sensitive to details like piping practices, moisture control, and defrost/condensate handling.

Identifying the major assemblies

Condensing unit (usually outside the box)

Typically includes:

• Compressor (often hermetic or semi-hermetic depending on application)
• Condenser coil and condenser fan(s)
• Receiver (common in many refrigeration systems to store refrigerant; not present on every design)
• Service valves and sometimes controls like high/low pressure switches

Remote evaporator (inside the refrigerated space)

Typically includes:

• Evaporator coil
• Evaporator fan(s) (air unit cooler)
• Expansion device (often a TXV)
• Defrost system (time clock/control; electric or hot-gas depending on design)
• Drain pan and drain line (critical for freezer applications to prevent ice problems)

How this differs from “central AC” installation

The refrigeration cycle is the same conceptually, but remote-evaporator refrigeration adds practical constraints:

• Longer line sets and elevation changes are common—piping must be designed to return oil to the compressor and avoid trapping liquid refrigerant.
• Lower evaporator temperatures (especially freezers) make moisture control and insulation more critical.
• Defrost and drain heat considerations are bigger because freezing conditions can block drains quickly.

Rather than memorizing one “universal piping rule,” the safe approach is to follow the manufacturer’s piping design guidance for:

• maximum line lengths
• vertical rise limits
• required traps
• line sizes

Installation goals (what you’re trying to prevent)

When installing a condensing unit + remote evaporator, your work should prevent these common failure modes:

• Refrigerant leaks (loss of charge, contamination ingress)
• Moisture/air in the system (ice at metering device, corrosion, poor performance)
• Poor oil return (compressor damage)
• Floodback or slugging (liquid refrigerant returning to compressor)
• Iced drains and water damage (especially in freezers)

Key installation steps (with the “why” behind each)

1) Equipment placement and environment

• Place the condensing unit where it can reject heat: good airflow, clean air path, service access.
• Place the evaporator to promote even air circulation in the box and avoid short-circuiting supply air directly back into the return.

Why it matters: uneven airflow creates hot spots, product issues, and coil icing in localized areas.

2) Refrigerant piping: suction, liquid, and sometimes additional lines

Most systems use at least:

• Suction line (evaporator outlet back to compressor)
• Liquid line (from condensing unit/receiver to TXV)

Some systems may also include defrost-related or control-related piping (system-dependent). What’s universal is the need for:

• correct pipe sizing
• proper supports
• insulation where required (especially suction lines and, in low-temperature systems, sometimes liquid lines to prevent flashing)
• correct pitch and trapping practices to return oil

3) Filter-drier and sight glass (common refrigeration accessories)

Many refrigeration installations include a filter-drier in the liquid line to capture moisture/acid/particles, and often a sight glass to observe liquid condition.

Why it matters: in refrigeration, small amounts of moisture can cause big problems at low temperatures. A properly installed drier is cheap insurance.

4) Leak testing and evacuation

Because you field-install more piping than with a packaged unit, contamination control is a major skill:

• Leak test with dry nitrogen per manufacturer practices.
• Evacuate thoroughly with an appropriate vacuum pump and tools.

Common mistake: “cracking” refrigerant to push air out instead of evacuating correctly—this is poor practice and may violate regulations. Proper evacuation is the correct technical method for removing noncondensables and moisture.

5) Charging and operational checks

Charging method depends on system design and refrigerant, but your goal is correct feeding of the evaporator without sending liquid back to the compressor.

In operation, you often evaluate:

• Superheat at evaporator outlet (to ensure vapor returning, not liquid)
• Subcooling (to ensure solid liquid feeding the metering device)

Worked example (conceptual): calculating subcooling

You measure liquid pressure and determine saturation temperature is $95\,^{\circ}\text{F}$. The liquid line temperature measured is $85\,^{\circ}\text{F}$.

$\text{Subcooling} = 95\,^{\circ}\text{F} - 85\,^{\circ}\text{F} = 10\,^{\circ}\text{F}$

You would compare that to manufacturer targets for the condensing unit and operating conditions.

6) Defrost and drain setup

For coolers, drains may flow by gravity. For freezers, drains can freeze if not protected.

Why it matters: a blocked drain causes water to overflow into the box, then freeze—leading to slip hazards, product issues, and fan/coil damage.

Installation includes:

• correct drain line slope and routing
• insulation or heat (where required by design)
• verifying defrost termination and fan delay settings (system-specific)

Example: “Short cycling” after installing a condensing unit

If a new system starts and stops frequently, don’t assume it’s only an electrical defect. Consider installation-related causes:

• condenser airflow restricted (high pressure safety trips)
• incorrect control settings or miswired pressure controls
• noncondensables left in the system (poor evacuation) leading to elevated head pressure
• incorrect refrigerant charge or liquid line restrictions

Exam Focus

• Typical question patterns:
  • Identify which components belong to the condensing unit vs. the remote evaporator.
  • Explain why evacuation and moisture control are especially important in refrigeration.
  • Given a scenario (iced evaporator, warm box, high head pressure), select likely installation errors (airflow, piping, defrost, drainage).
• Common mistakes:
  • Treating refrigeration piping like short split-system runs—ignoring oil return considerations and manufacturer line sizing guidance.
  • Skipping or rushing evacuation, leading to ice at the metering device and unstable operation.
  • Neglecting drain/defrost details in low-temperature applications, causing chronic icing and callbacks.