🚧 Under construction — VoTechWorks is being built. A free tech program — complimentary, as our commitment to get America working.
voTechWorksGrade 13 · a vocational technology learning center, by urbanicity
newSchoolWorks.com › VoTechWorks › Building & Construction › HVAC/R › Externship / Worksite Placement › Lesson 2
BLD-HVAC07-09 · Lesson 2 · 100 clock hours · field

Installation and Rough-In Field Tasks

Objective. The student will assist with or lead, as assigned, the installation and rough-in of residential and light-commercial HVAC/R systems — including equipment placement, electrical connections, refrigerant line sets, and ductwork connections — meeting the employer's quality and schedule standards.

Installation and Rough-In Field Tasks

The externship placement puts you on a real jobsite alongside a licensed journeyman. During installation and rough-in work, you are responsible for doing the job correctly, safely, and on schedule. This lesson walks through every major task you will perform so that you arrive on-site prepared.

Equipment Placement and Rigging

Before any refrigerant or wiring is touched, the equipment must be positioned correctly. Condensing units are set on a level pad — concrete, composite, or equipment feet — high enough to keep the base above grade drainage and clear of debris. Check the manufacturer installation manual for minimum clearances on all four sides and above the unit; insufficient clearance reduces airflow and efficiency. Air handlers are mounted in the attic, closet, or utility room with a drain pan and primary condensate drain sloped toward the outlet. Furnaces are positioned so the flue collar aligns with the vent chase and the return-air opening faces the return plenum. Level equipment before making any connections.

Electrical Connections

Lockout/tagout (LOTO) is mandatory before touching any electrical component. Apply an approved lockout device to the disconnect, verify absence of voltage with a non-contact tester, and tag the device with your name and the date. Condensing units require a dedicated disconnect within sight of the unit per the National Electrical Code. Wire gauge and breaker size must match the unit nameplate's minimum circuit ampacity (MCA) and maximum overcurrent protection (MOCP). At the control board, connect low-voltage thermostat wires to the labeled terminals (R, C, Y, G, W, etc.) and secure all wire harnesses. After wiring is complete, have the journeyman verify before restoring power.

Refrigerant Line Sets

Line sets carry refrigerant between the condensing unit and the air handler. Copper tubing must be sized per the manufacturer specification — oversized or undersized lines cause capacity and oil-return problems. Follow these steps in order:

1. Run the line set with as few bends as possible; use a tubing bender to avoid kinks.

2. Support lines every 6 feet horizontally and at every vertical change of direction.

3. Insulate the suction (larger) line fully with foam insulation rated for outdoor UV exposure where exposed to sunlight; the liquid (smaller) line may also require insulation per the manufacturer.

4. Before connecting to the system, pressure-test the line set with dry nitrogen — never oxygen or shop air — to the pressure specified in the installation manual. Hold pressure for a minimum of 15 minutes and verify no drop on the gauge.

5. After passing the nitrogen test, connect the lines, install the service valves, and pull a deep vacuum with the vacuum pump. Do not charge until the system reaches the evacuation level required by the manufacturer (typically 500 microns or lower, verified with a micron gauge).

Nitrogen cylinders must always be used with a regulator. Never open a nitrogen cylinder without a regulator attached — unregulated pressure can rupture copper tubing and cause serious injury.

Ductwork Connections and Fabrication

On rough-in day, you will fabricate transitions, hang flex-duct runs, and install register boots. Use tin snips for sheet-metal cuts; wear cut-resistant gloves — sheet-metal edges are sharp. Seal all duct connections with mastic (brush-applied) or UL 181-rated foil tape; standard cloth duct tape is not code-compliant for duct sealing. Flex duct must be fully extended — never compressed — and supported so it does not sag more than 1 inch per foot of run. Measure each run, record the length and duct diameter in your field log, and note any field modifications such as added elbows or offsets.

Startup and Documentation

Once the system is wired, charged, and sealed, you will assist with startup. Record in your field log:

Accurate documentation is not optional. It is your professional record and may be required for warranty registration, code inspection, and employer quality review.

Safety Summary

Key terms9

Minimum Circuit Ampacity (MCA)The minimum wire ampacity required for the circuit feeding HVAC equipment, calculated from the unit nameplate and used to select the correct wire gauge.
Maximum Overcurrent Protection (MOCP)The largest fuse or breaker size permitted for a given piece of equipment, as stated on the unit nameplate.
Lockout/Tagout (LOTO)An OSHA-required safety procedure that isolates and de-energizes equipment and physically locks the energy-isolating device before any maintenance or wiring work begins.
Nitrogen Pressure TestA leak-check procedure using dry nitrogen gas pressurized through the refrigerant line set or system to confirm there are no leaks before evacuation and charging.
Evacuation (Deep Vacuum)The use of a vacuum pump to remove air and moisture from a refrigerant system to a very low pressure level, typically verified in microns with a micron gauge, before refrigerant is introduced.
Static PressureThe pressure exerted by air against the walls of the ductwork, measured in inches of water column; supply and return static readings together indicate system airflow resistance.
MasticA flexible, brush-applied sealant used on duct joints and connections that remains pliable after curing, providing an airtight, code-compliant seal.
Line SetThe pair of copper refrigerant lines — suction (larger, insulated) and liquid (smaller) — that connect the condensing unit to the air handler or evaporator coil.
Service ValveA manually operated shutoff valve on the condensing unit that allows the technician to isolate the system for service, recover refrigerant, or connect gauges.

Worked examples4

1. A condensing unit nameplate shows MCA = 23 A and MOCP = 40 A. The electrician asks what the minimum wire size and maximum breaker size are. What do you tell them?
  1. Step 1 – Identify MCA: The MCA is 23 A. Wire must be rated for at least 23 A continuous. Per standard wire tables, 10 AWG copper (rated 30 A at 60 °C) meets or exceeds 23 A, so 10 AWG is the minimum acceptable wire gauge.
  2. Step 2 – Identify MOCP: The nameplate states 40 A maximum. A standard 40 A breaker (or time-delay fuse) is the largest overcurrent device permitted.
  3. Step 3 – State the answer clearly for the electrician: minimum 10 AWG copper wire; maximum 40 A overcurrent device.
Answer: Minimum wire: 10 AWG copper. Maximum breaker or fuse: 40 A. Always defer to the nameplate values — they are the legal limits for that specific unit.
2. You are pressure-testing a line set. After pressurizing to the manufacturer's specified test pressure with nitrogen, you watch the manifold gauge for 15 minutes. The gauge starts at 150 psig and reads 147 psig at the end. Does the line set pass or fail? What is the pressure drop?
  1. Step 1 – Calculate pressure drop: 150 psig − 147 psig = 3 psig drop over 15 minutes.
  2. Step 2 – Evaluate: Any measurable pressure drop indicates a leak. The line set fails the pressure test.
  3. Step 3 – Next action: Locate the leak using an electronic leak detector or approved leak-check solution (never open flame), repair it, re-pressurize, and retest until the gauge holds steady for the full hold time with zero drop.
Answer: Pressure drop = 3 psig. The line set fails. Any drop in pressure during the hold period means there is a leak that must be found and repaired before evacuation.
3. A flex-duct run must travel 14 feet from the plenum to a register boot. Code requires support so sag does not exceed 1 inch per foot of run. What is the maximum allowable total sag for this run, and how often must supports be placed if each support span is limited to 4 feet?
  1. Step 1 – Maximum sag: 1 inch per foot × 14 feet = 14 inches total allowable sag across the full run. In practice, each individual span between supports must not sag more than 1 inch per foot of that span.
  2. Step 2 – Number of supports: Divide total run by maximum span — 14 ft ÷ 4 ft per span = 3.5. Round up to 4 spans, meaning you need at least 3 intermediate supports plus the connections at each end (plenum collar and register boot), for 5 total attachment points.
  3. Step 3 – Record in field log: run length (14 ft), duct diameter, number of supports, and hanger type used.
Answer: Maximum allowable sag = 14 inches over the full run (1 in/ft). A minimum of 3 intermediate supports are required in addition to the two end connections, creating 4 spans of no more than 4 feet each.
4. At startup, your manometer reads 0.45 in. w.c. on the supply side and −0.18 in. w.c. on the return side. What is the total external static pressure (TESP), and why does it matter?
  1. Step 1 – TESP formula: TESP = supply static pressure + absolute value of return static pressure.
  2. Step 2 – Calculate: TESP = 0.45 + 0.18 = 0.63 in. w.c.
  3. Step 3 – Compare to design: Most residential systems are rated for 0.50 in. w.c. TESP. A reading of 0.63 in. w.c. exceeds the design point, which means airflow is lower than rated — this can cause reduced efficiency, coil freezing, or comfort complaints. The technician should inspect filters, duct restrictions, or undersized return grilles.
Answer: TESP = 0.63 in. w.c. This exceeds the typical 0.50 in. w.c. design limit, indicating excessive system resistance that must be investigated and corrected.

The math in this lesson2

Learners apply 1 inch per foot to a 14-foot flex run to find maximum allowed sag.
6.RP.37.NS.1
In class: Assist the journeyman on a minimum of four complete split-system or package-unit installations: set the condensing unit, mount the air handler or furnace, run and insulate the refrigerant line set, make electrical connections at the disconnect and control board, and verify refrigerant line integrity with a nitrogen pressure test before evacuation. · Fabricate and hang duct transitions, flex-duct runs, and register boots under journeyman direction, then record measurements, materials used, and any field modifications in the daily field log. · Document each installation job in the field log: equipment model and serial numbers, measured supply and return static pressures after startup, outdoor ambient and indoor return temperatures, suction and discharge pressures at startup, and the name of the journeyman who verified the readings.
Materials: Employer-issued hand tools and power tools, manifold gauge set, vacuum pump, nitrogen cylinder and regulator, leak detector (electronic), refrigerant recovery machine, duct installation kit (tin snips, sheet-metal screws, mastic, foil tape), field log binder, manufacturer installation manuals
Check: Journeyman supervisor scores each installation task on the employer evaluation rubric (minimum 3 out of 4 on every category: safety, technique, documentation, and professionalism); field log entries are complete and legible for every job day — any score below 3 triggers a documented corrective-action discussion within 48 hours.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Safety and OSHA compliance
1. Before making any wiring connections at the condensing unit disconnect, which action must be performed first?
EPA 608 / refrigerant handling and safety
2. Which gas is correct to use for pressure-testing a refrigerant line set before evacuation?
NATE / electrical systems
3. A unit nameplate shows MCA = 18 A and MOCP = 30 A. Which combination is correct for this installation?
HVAC Excellence / installation procedures
4. After a 15-minute nitrogen pressure hold test, the gauge shows a 2 psig drop from the starting pressure. What is the correct next step?
NCCER HVAC / duct systems
5. Which duct-sealing material is code-compliant for sealing sheet-metal duct joints?
NATE / air distribution and measurement
6. When calculating Total External Static Pressure (TESP), a technician reads 0.50 in. w.c. on the supply and −0.20 in. w.c. on the return. What is the TESP?
NCCER HVAC / professional documentation
7. Which item is NOT required to be recorded in the field log at system startup according to this lesson?
NCCER HVAC / duct installation
8. A flex-duct run is 8 feet long. Supports must be placed so sag does not exceed 1 inch per foot of run and spans are no longer than 4 feet. How many intermediate supports (not counting the two end connections) are needed at minimum?
Record this lesson on my transcript. Sign in with your key and enrollment email to record lessons (enroll free if you have no key). This page stays open to read and practise.
← Previous lessonProgram planNext lesson →