313D System Installation and Startup 2 — Questions and Answers
Question 1: When installing a split-system condenser outdoors, what is the minimum recommended clearance from the top of the unit to any overhead obstruction?
- 12 inches
- 24 inches
- 36 inches
- 48 inches (Correct answer)
Correct answer: 48 inches
Most manufacturers require at least 48 inches of clearance above the condenser to allow unrestricted discharge airflow and prevent hot air recirculation.
Question 2: During system startup, the technician measures suction pressure lower than expected and superheat higher than normal. What is the most likely cause?
- Overcharge of refrigerant
- Restricted liquid line filter-drier (Correct answer)
- Excessive airflow across the evaporator
- Oversized metering device
Correct answer: Restricted liquid line filter-drier
A restricted liquid line filter-drier causes a pressure drop that starves the metering device, resulting in low suction pressure and high superheat.
Question 3: What is the purpose of installing a crankcase heater on a scroll compressor before startup?
- To increase discharge pressure during startup
- To boil off refrigerant that has migrated into the oil (Correct answer)
- To pre-lubricate the compressor bearings
- To prevent high-pressure lockout on cold days
Correct answer: To boil off refrigerant that has migrated into the oil
Crankcase heaters vaporize liquid refrigerant that has migrated into the compressor oil sump, preventing slugging damage on startup.
Question 4: When connecting refrigerant line sets, which brazing rod alloy is preferred to minimize oxidation scaling inside copper tubing?
- Stay-Silv 15 with nitrogen purge (Correct answer)
- Silfos 0 without flux
- Harris 56 with flux
- Tin-lead solder with rosin flux
Correct answer: Stay-Silv 15 with nitrogen purge
Stay-Silv 15 (15% silver) used with a nitrogen purge prevents oxidation scale formation inside the tubing that could contaminate the system.
Question 5: A residential condensing unit is installed on a rooftop. Which installation precaution is most important for preventing vibration transmission to the structure?
- Securing refrigerant lines with metal clamps every 6 feet
- Using rubber isolation pads or spring isolators under the unit (Correct answer)
- Insulating the suction line with foam wrap
- Installing a liquid line solenoid valve
Correct answer: Using rubber isolation pads or spring isolators under the unit
Rubber isolation pads or spring isolators absorb compressor vibration and prevent it from transmitting through the structure and causing noise complaints.
Question 6: During a new installation leak check using nitrogen, at what pressure should the technician hold the system before releasing and checking for leaks?
- 25 psig for 10 minutes
- 150 psig for 24 hours (Correct answer)
- The maximum operating pressure plus 10%
- Triple the low-side design pressure
Correct answer: 150 psig for 24 hours
Industry best practice calls for pressurizing with dry nitrogen to 150 psig and holding for at least 24 hours to confirm no pressure drop from leaks.
Question 7: Which document must be completed and left with the homeowner after completing a new residential AC installation?
- EPA 608 certification copy
- Manufacturer's warranty registration and startup checklist (Correct answer)
- Technician's refrigerant purchase receipt
- Local building permit application
Correct answer: Manufacturer's warranty registration and startup checklist
Manufacturer warranty registration and the startup checklist must be completed and provided to the homeowner to validate the warranty and document system commissioning.
313D System Installation and Startup 2
When installing a split-system condenser outdoors, what is the minimum recommended clearance from the top of the unit to any overhead obstruction?