How to Replace a Complete HVAC System

This article is for professionals or people with proper HVAC certifications. Always follow local codes and manufacturer instructions.

Contents

1. Pre-Installation Planning

2. Safety and Initial Shutdown

3. Pumping Down the Old System & Recovering Refrigerant

4. Removing the Old Equipment

5. Installing the New Systems (Condenser, Coil, Furnace)

6. Electrical, Refrigerant, and Control Connections

7. Final Testing, Commissioning & Customer Walk-through

8. Maintenance Tips and Best Practices

9. Summary & Key Takeaways

10. References

1. Pre-Installation Planning

1.1 Load Calculation & Equipment Sizing

Before replacing a system, you should confirm that your new equipment is properly sized. Oversized or undersized equipment causes comfort issues and efficiency loss.

1.2 Confirm Compatibility

In a full replacement (furnace, coil, condenser) you need to ensure the new evaporator coil matches the furnace/plenum, the line-set length is appropriate, and the condenser can accept the refrigerant.

1.3 Site Preparation

Clear space around system, protect flooring, have drop cloths, confirm access routes for removal and installation. As noted in homeowner guides, this helps make the job smooth.

1.4 Acquire Permits & Check Codes

Since you’re dealing with refrigerants, gas lines, electrical work and structural supports, check local building codes (often guided by standards such as the Uniform Mechanical Code).

2. Safety and Initial Shutdown

1. Turn off the electrical breaker for the entire system to ensure no power.

2. Shut off the gas supply at the meter (if replacing a gas furnace).

3. Verify zero voltage before touching wiring.

4. Wear personal protective equipment (PPE): gloves, safety glasses, insulated tools.These steps are vital because you’re working with live circuits, pressurized refrigerant lines, gas valves and heavy equipment.

3. Pumping Down the Old System & Recovering Refrigerant

In the replacement described, an existing condenser using R-22 was being replaced. The process included locking refrigerant in the old condenser unit for later recovery.

Steps

• Remove service caps from the liquid and suction lines.

• Close the specialty service valves (king valves) on the outside unit to isolate refrigerant.

• Use the compressor in the outdoor unit to pull refrigerant from the evaporator coil and line set into the condenser.

• Attach gauges and watch the suction side pressure drop to zero before final shut-off.This method prevents refrigerant discharge and ensures the system is safely prepared for removal.

  
  

  Note: Only certified HVAC technicians may handle refrigerants due to environmental regulations.

4. Removing the Old Equipment

4.1 External Unit

• Once refrigerant is secured, disconnect electrical and refrigerant line connections.

• Remove outdoor unit from its pad. Inspect pad for levelness; modern units may require a new pad due to size differences. Fire & Ice

4.2 Indoor Coil & Furnace

• Disconnect the plenum and remove the old coil and furnace.

• If replacing the furnace and coil, remove both.

• Dispose properly according to local regulations.

5. Installing the New Systems

5.1 New Furnace & Evaporator Coil

• Place the furnace on a level base and ensure proper duct connection.

• Install the new evaporator coil within the plenum above or beside the furnace, ensuring correct orientation and air flow.

• Install a 4-inch filter rack if specified (as in the original transcript).

5.2 Outdoor Condenser

• Set the new condenser on a properly leveled pad with adequate clearance for air flow and maintenance.

• Connect the refrigerant line set between the indoor coil and outdoor unit.

5.3 Refrigerant Line Set & Insulation

• Ensure the line set is sized correctly and securely mounted.

• Insulate the suction line to prevent condensation and loss of cooling capacity.

6. Electrical, Refrigerant and Controls

6.1 Electrical Connections

• Connect the power supply to the new furnace and outdoor unit via proper disconnects and breakers.

• Ensure wiring is to manufacturer specifications and follows the NEC/local code.

6.2 Refrigerant System Charging

• Vacuum the system to remove air and moisture.

• Open the refrigerant valves and allow proper charge according to manufacturer specifications.

• In the transcript, the technician used a manual contactor push to verify suction pressure drop to zero before final shut-off.

6.3 Thermostat & Controls

• Install or verify the thermostat wiring.

• Configure system controls (e.g., cooling, heating modes) and verify operation.

7. Final Testing, Commissioning & Customer Walk-through

7.1 System Testing

• Turn on the system and verify that all modes (cooling and heating if applicable) function properly.

• Check airflow at registers, examine filter placement, confirm refrigerant lines are insulated, listen for unusual noises.

• Verify efficiencies and make any necessary adjustments (in larger installations, testing, adjusting and balancing – “TAB” – may apply). Wikipedia

7.2 Clean-Up and Documentation

• Remove all debris and old equipment. Leave the job site clean.

• Provide the homeowner with equipment manuals, warranty cards, and maintenance instructions.

7.3 Customer Walk-through

• Show the homeowner how to use the thermostat and basic system features.

• Explain filter maintenance, what to expect in the first few hours/days of operation, and signs of trouble.

8. Maintenance Tips and Best Practices

• Advise the homeowner to check and replace air filters regularly (every 1–3 months).

• Recommend annual professional maintenance to maximise system life and efficiency. nextlevelhvac.net

• Ensure condensate drains are clear and refrigerant line insulation remains intact.

• Educate on keeping the outdoor condenser clear of plants, debris or overgrowth.

9. Summary & Key Takeaways

Replacing a full HVAC system is a major job but very manageable when broken down into clear phases: planning, shutdown, refrigerant recovery, removal, installation, connection and testing. Key points:

• Always prioritise safety (electrical, gas, refrigerant).

• Ensure sizing and compatibility from the outset to avoid inefficiency.

• Follow proper refrigerant recovery and vacuum procedures.

• Make sure installations meet or exceed code and manufacturer instructions.

• Test thoroughly and leave the homeowner educated and prepared. By following these steps and best practices, you’ll set up a system that delivers comfort and efficiency for years.

References

• “Guide to HVAC Installations | Process, Cost & More.” Carrier. Carrier

• “Step-By-Step HVAC System Installation Guide.” Erie Institute of Technology. Erie Institute of Technology

• “Air Conditioning Installation: A Step-by-Step Process.” NexGen Air & Plumbing. nexgenairandplumbing.com

• “HVAC Installation.” BuildOps Business Toolkit. BuildOps

• “A Homeowner’s Guide to Residential HVAC Installation.” FC Comfort.