HVAC

I'm checking charge on a straight-cool split with a fixed-orifice (piston) metering device. What do I measure and what am I looking for?

Same question but the system has a TXV. What's my charging target and where do I take the readings?

Why do the old guys insist on flowing nitrogen through the lineset while brazing, and how much flow is right?

What's the accepted evacuation target and decay test before I release charge on a new residential split system, and where should the micron gauge be?

Do I charge R-410A as a liquid or a vapor, and why does it matter?

Customer says her AC 'isn't cold enough.' What temperature split across the evaporator should I expect and what does it depend on?

How do I actually verify airflow on a residential air handler instead of assuming 400 CFM per ton, and what static pressure numbers should worry me?

Why does an air handler with the coil upstream of the blower need a P-trap on the condensate drain, and how deep should it be?

I've got a condenser that has to sit 110 feet of line from the air handler, with the air handler 30 feet above the condenser. What do I need to think about beyond just running bigger copper?

Condenser fan runs but compressor just hums and trips. I suspect the capacitor. How do I test it and pick the replacement?

Heat pump customer thinks the unit is broken because it 'blows cold' and 'steams' for a few minutes on a cold morning. Explain what's actually happening and when it's a real problem.

Homeowner wants me to just replace his 3-ton with a 4-ton because 'bigger is better' in Florida. Make the case for doing a load calc instead, including what inputs actually drive it.

I'm laying out ductwork for a new 3-ton system. Walk me through how Manual D actually sizes the trunks and branches, in plain terms.

I've installed a new 80,000 BTU gas furnace. How do I check temperature rise and what do I do if it's out of range?

What manifold pressure should a natural-gas furnace run, what about propane, and what actually has to change to convert one to LP?

Doing a combustion analysis on a 90+ condensing furnace. What readings am I looking for and which number is the stop-the-job number?

Compressor pulls high amps at startup and sometimes trips. How do I tell a weak compressor from a start problem, and when is a hard-start kit the right answer?

I'm pulling the compressor on a 4-ton R-410A split. How far do I have to pull the refrigerant down before I open the system, legally?

TXV system is hunting - superheat swings from 3 to 20 degrees every couple minutes. Where do I look, and how should the sensing bulb be mounted?

Doing my first ductless mini-split. Any tips on the flares so it doesn't leak?

Putting an air handler in an attic over a finished ceiling. What does code require for condensate overflow protection?

In Florida specifically, is there anything extra on that attic condensate rule for a downflow unit or on the refrigerant service ports?

Installing a 100,000 BTU/h 80% gas furnace in a utility closet that's 6 by 8 feet with a 9-foot ceiling. Does the closet give it enough combustion air, and if not what do I need?

Where does the gas shutoff valve have to be for a furnace, and do I need a drip leg?

New construction in Florida with the ducts in the attic. What's the duct leakage test requirement and what number do I have to hit?

Can my helper buy a jug of R-410A and swap a condenser on his own house without a card?

Rules for putting a furnace or air handler in an attic - access, walkway, working space?

Electrician isn't coming back. For the condenser, where does the disconnect have to be, and how do I size the breaker and wire off the nameplate?

Tech is at a 3-ton R-410A TXV system on a 68 F afternoon in October. He hooks up gauges, sees 105 psi suction, says 'that's low for 410,' and starts adding refrigerant until suction reads 118 and the line is sweating. Subcooling is now 22 F. What did he do wrong?

New install: crew brazed the lineset without nitrogen, pulled a vacuum to 500 microns, charged by weight, and it ran great. Three weeks later the customer calls: system runs, suction line is frosting back to the compressor, then it goes to 45 psi and the coil ices. What happened and what's the fix?

Homeowner's condenser died on an older R-22 system. Contractor quoted 'condenser only' and is installing a new R-410A condensing unit on the existing indoor coil and copper, planning to flush the lineset. What's wrong?

Apprentice is pulling a vacuum on a new mini-split with a standard manifold set, both Schrader cores in, 1/4 in. hoses, micron gauge screwed onto the pump's inlet tee. After 45 minutes the gauge says 300 microns so he closes the gauges and opens the service valves. Next day the system is short on capacity. What went wrong?

Attic horizontal air handler: crew set it on a new 2-inch aux pan with a float switch in the pan, ran the primary 3/4 PVC out to the eave with a P-trap, put a vent tee between the coil and the trap, and tied the float switch into the R wire. Homeowner has ceiling damage six weeks later. Where's the error?

New 4-ton system, 1,600 CFM design. Installer ran 8-inch flex to eight supply registers, each run 25-40 feet, stapled to trusses every 6 feet, a couple runs make hard turns around the ridge. Return is a single 16x25 filter grille with a 14-inch flex run. Static pressure measured at 1.1 in. w.c. Where did it go wrong?

Jacksonville: 2,000 sq ft slab house, decent windows, attic ducts. Salesman sized it at 5 tons ('400 sq ft per ton plus a cushion for Florida') single-stage with a 5-ton air handler, no load calc. Homeowner is at 74 F on the thermostat but says the house feels sticky and the unit runs 8 minutes at a time. What's going on and what should have happened?

Compressor grounded out on a 3-ton R-410A heat pump. Tech recovered, swapped the compressor, replaced the liquid line drier, pulled a vacuum, weighed in the charge, and left. It ran 5 weeks and the new compressor failed the same way. What did he miss?

Gas furnace lives in a 3x6 closet off the hallway. Previous contractor cut a big return grille into the closet door and pulled return air straight from the closet through the furnace's open filter slot. Furnace is a standard 80% with a B-vent through the roof. Combustion analyzer reads 200 ppm CO in the flue and goes up when the door closes. What's the failure?

Heat pump air handler with a 10 kW strip kit (nameplate says 41 A heater, MCA 52, MOP 60 for the combined unit). Installer brought #8 NM-B on a 50 A breaker because 'the heater is 41 amps.' Also landed the blower and strips on that one circuit. What's the problem?

Installer put a 24,000 BTU mini-split with a 115-foot lineset from the roof down to a first-floor head, ran the lines through a mess of elbows, didn't add any refrigerant beyond the factory charge, and set the outdoor unit on the ground under a deck with about 8 inches of clearance above the fan. Runs poorly and overheats on hot days. What did he miss?

Homeowner switched the house from propane to natural gas. The 'plumber' hooked the existing LP furnace and water heater up to the new natural gas meter and set the furnace's manifold pressure from 10 down to 3.5 in. w.c. Both appliances light. What's about to happen?