System Installation and Startup Flashcards

When installing refrigerant line sets that run through an exterior wall, what is required at the penetration point?

Answer: A sealed weather-tight fitting or escutcheon with sealant to prevent air and moisture infiltration

Penetrations through exterior walls must be sealed with weather-tight fittings and sealant to prevent conditioned air loss, moisture entry, and pest infiltration.

A technician installs a new 3-ton split system and measures 380 CFM of airflow across the evaporator. What problem does this create?

Answer: Low airflow leading to evaporator freeze-up and reduced capacity

Standard design calls for 400 CFM per ton (1,200 CFM for 3 tons); 380 CFM is severely low and will cause the evaporator coil to freeze due to insufficient heat transfer.

During equipment startup, the compressor short-cycles off on the high-pressure switch after 2 minutes. What should the technician check FIRST?

Answer: Condenser fan motor operation and airflow restriction

Condenser fan failure or blocked airflow is the most common cause of high-pressure trips because discharge heat cannot be rejected, causing pressure to spike.

Which refrigerant characteristic requires that R-410A systems use POE (polyolester) oil instead of mineral oil?

Answer: R-410A is not miscible with mineral oil, preventing proper oil return

R-410A is not miscible with mineral oil, so it cannot carry oil through the refrigerant circuit for proper lubrication; POE oil mixes well with R-410A ensuring oil return.

A new installation has the outdoor unit located 60 feet below the indoor unit. What additional installation step is required for the refrigerant piping?

Answer: Install oil traps in the suction line riser every 20 feet

When the condenser is below the evaporator and the suction line rises vertically, oil traps every 20 feet in the riser ensure oil returns to the compressor against gravity.

What is the correct method for charging a new R-410A system that was evacuated and requires a full charge per manufacturer nameplate?

Answer: Charge liquid refrigerant through the high-side service port with the system off

R-410A is a near-azeotrope that must be charged as liquid to maintain proper composition; liquid is introduced through the high-side with the system off for a full initial charge.

During startup commissioning, a technician records a temperature difference of only 12°F between supply and return air. What is the most likely cause?

Answer: Insufficient airflow or low refrigerant charge reducing capacity

A normal Delta-T is 16–22°F; a low Delta-T of 12°F indicates reduced system capacity from low airflow, low refrigerant charge, or both limiting heat transfer.