HVAC Service Technician
HVAC & MechanicalWalk me through diagnosing a rooftop unit that cools fine in the morning and short-cycles by two in the afternoon.
What superheat would you expect on a properly charged R-410A system, and what does it tell you when it reads high?
A tenant says it is too warm and the space is at setpoint. What do you check and in what order?
A rooftop unit trips on high head pressure only on hot afternoons. Where do you start, and what would rule the condenser out?
How do you tell a failed run capacitor from a failing compressor on a call-out, with no parts on the truck?
A customer has had three technicians out for the same intermittent fault. What do you do differently on the fourth visit?
When do you recover and weigh in a charge rather than top it up, and how do you make that call?
Walk me through everything you check before you condemn a compressor.
When do you use subcooling rather than superheat to judge a charge?
A unit is running but not cooling well and the charge checks out. Where do you go next?
Tell me how an economizer is supposed to work, and the three ways you most often find them broken.
Hand me a wiring diagram for a unit you have never seen. How do you use it?
Describe your lockout procedure on a rooftop unit with a disconnect you cannot see from where you are working.
Talk me through recovering refrigerant from a unit you are replacing.
Explain to me, as if I am the building manager and not a technician, why the unit failed.
What stops you from going up on a roof?
Listen for
- Talks in symptoms and causes rather than part numbers - superheat and subcooling readings, not "I replaced the TXV"
- Has worked unaccompanied on rooftop equipment, not just assisted on installs
- Can describe a call they diagnosed wrong and what the second visit found
The mistake
The mistake this seat invites. Hiring on EPA 608 and years of experience without testing diagnostic reasoning. The certification is a floor, not a signal, and residential-heavy experience transfers badly to rooftop and chiller work.