Yes — voltage is a ceiling, not a match requirement. A 440V cap on a 370V application is fine and it's why most trucks just stock 440V rounds. Never the reverse. MFD still has to match exactly.

Heat, voltage spikes, or a motor on its way out. Check the fan motor's amp draw against nameplate — a dragging motor cooks caps as a symptom, not a cause. Also look at where the cap lives: baking against a hot compressor shortens its life, and undersized replacements fail fast.

It's done. The bulge is the pressure-relief top deforming, which means the dielectric has been cooking. It may still read close to spec today and strand the customer next week — replace it while you're standing there.

Not banned — production of new 410A steps down, but the installed base runs for another 15+ years on virgin and reclaimed supply, same story as R-22. Nobody should scrap a working system over refrigerant headlines. Prices will drift up slowly; that's the whole drama.

No. Different refrigerants, different pressures, and a mixed charge is unrecoverable — you'd be signing up for a full recovery, deep vacuum, and recharge. Every system gets its nameplate refrigerant, period.

Yes — federal rule, not store policy. Section 608 certification is required for purchase of regulated refrigerants, and any counter that skips checking is risking fines for both sides. Bring the card once; a good counter keeps it on file.

It's printed in the unit's install manual as ounces per foot of liquid line beyond the rated length — commonly around 0.6 oz/ft for 3/8" liquid lines, but use the table for your exact model. Weigh it in on long runs; chasing subcooling from a wrong factory charge wastes an afternoon.

Necessary. Brazing copper in open air lines the pipe with black oxide scale that ends up in the TXV and the compressor. A lazy 2-3 SCFH nitrogen purge while you braze keeps the inside clean — it's the cheapest system protection there is.

Sometimes physically, rarely wisely. Mismatched coils cost capacity and efficiency, can void the AHRI match and rebate paperwork, and with the R-454B transition the refrigerant usually won't even line up. Quote the matched system; explain it as protecting the compressor's warranty.

Venting. An 80% breathes through existing metal B-vent; a 96% wants PVC out the sidewall plus a condensate drain. In a retrofit where the venting path is ugly, the install cost difference can eat a decade of gas savings. In propane country the math tilts back toward 96% — LP is expensive fuel.

Down for cooling-dominated homes, up only when heating drives the design and you've got cold-climate equipment. Oversized cooling short-cycles, dehumidifies badly, and wears parts. The load calc is the answer; the bigger box is the temptation.

Check the easy stuff in order: failing run capacitor, then compressor locked-rotor draw on start. A hard-start kit can rescue a marginal compressor on long rural power runs — but if the compressor is grounding out, no kit saves it. Confirm with a megohm check before promising miracles.

Yes. A TXV holds superheat across varying conditions, protecting the compressor and keeping capacity honest in our swing seasons. Fixed orifices are fine when everything matches the design day; mountain weather rarely does. Most current matched systems ship TXV anyway.

Sized to the heating load the heat pump can't cover at design temperature — not 'the biggest kit that fits.' Valley homes often live fine on 5–8 kW; high-elevation homes need more. Oversized strips just slam the panel and the bill. The load calc and the panel's capacity make the call.

Airflow or charge, almost always. Dirty filter, dead blower, crushed flex, or a coil matted with dog hair starve the evaporator; low charge does the same math. Thaw it fully, fix the airflow first, then check charge — icing that returns after both is TXV territory.

Defrost is normal; staying iced isn't. Check for low charge first (the classic), then airflow — dirty outdoor coil, blocked base pan drain refreezing, or the unit mounted where roof runoff drips into it. Mountain installs want the outdoor unit elevated above snow line on a stand or brackets.

The box price looks great until you need a board in February and nobody stocks it. Established brands cost more because the parts pipeline and the match tables exist. Whatever you hang on the wall, you're marrying its parts availability.

Short, tight, fully stretched runs from trunk to boot — flex is fine and fast. Long snaking runs, sag between joists, or compressed bends are where flex gets its bad reputation. The material isn't the problem; the installation usually is.

Condensation — the duct surface is below the dew point of humid crawl air. Fixes in order: seal duct leaks (leaking cold air chills the jacket), upgrade to R8 insulated duct, and address crawlspace moisture itself. Wrapping wet R4 in more plastic is not a fix.

The classic is 400 CFM per ton and roughly 0.1 in/100ft friction rate for residential — as a starting point, not a design. Real answer comes from Manual D against measured static. Most 'undersized equipment' complaints are actually duct systems choking a correctly sized unit.

Code-wise usually yes; performance-wise it's where flex sins hurt most — returns run at higher friction and every sag costs you. If you must, go big on diameter, keep it short and tight. Hard pipe returns are the difference customers can hear.

Tank in the yard or buried dome lid = LP. Meter on the wall = natural gas. It matters because orifices, regulators, and manifold pressures differ — running NG setup on LP over-fires the appliance. When converting, the kit is appliance-specific by model number.

Follow the specific product's listing — most CSST can't be direct-buried without a sleeve and has bonding requirements people skip. The bonding clamp costs a few dollars; lightning damage to unbonded CSST costs a house. Read the manufacturer's install guide, not the forum summary.

An approved appliance connector at the unit is legal and normal in most jurisdictions — one connector, right length, no passing through the cabinet wall, drip leg where required. Local inspectors vary; when in doubt, hard-pipe the last run and nobody argues.

Total BTU of everything on the line, longest-run method, against the sizing tables for your pipe type and pressure. Tankless units are gas hogs — 150–200k BTU — and the #1 install failure is hanging one off a line sized for a furnace alone. Run the table before you quote.

Either it's genuinely too cold for the heat pump (undersized or losing capacity), the balance point/lockout is set wrong, or the stat's staging is misconfigured. Aux running constantly turns a heat pump's economics upside down — set intelligent lockout and check the defrost cycle before blaming the equipment.

Nine times out of ten it's power: no C-wire and the stat is power-stealing from a board that hates it. Land a real common wire or use the add-a-wire module. The tenth time it's rural Wi-Fi that drops nightly — some houses just want a quality conventional stat.

Textbook dirty flame sensor. The burner lights but the sensor can't prove it, so the board drops the gas valve. Pull it, shine it with fine abrasive, re-seat. If cleaning stops holding, replace it — they're cheap. If a new sensor still drops out, then look at grounding and flame rectification.

Yes, and on every service call where one's missing. It's the cheapest part in the drain aisle versus a ceiling, and inspectors increasingly expect them. Wire it to kill the call for cooling, not just the blower.

At wholesale pump prices, no — replace it. Check the check-valve and discharge line first (a kinked line mimics a dead pump), then swap the unit and wire the safety contacts so the next failure shuts the system down instead of flooding the closet.

Defrost steam. The outdoor coil sheds its frost as a dramatic cloud of water vapor for a few minutes and homeowners call it in as smoke every cold snap. Real trouble smells electrical and doesn't stop when the cycle ends. Educate at install and save yourself the panic calls.

For coil mold in our humid climate, a coil-mounted UV lamp genuinely keeps the wet coil cleaner and protects capacity. As whole-air purification, claims outrun evidence. Sell it as coil hygiene with an annual lamp change, and it's an honest product.

Three things bite newcomers: elevation (a spec that works downtown fails at 4,000 ft — check heat pump capacity tables against real design temps), propane prevalence outside the gas grid (carry conversion kits), and vented crawlspaces that condense on everything all summer (R8 duct, sealed drains, float switches). Local experience is mostly knowing those three.

Above the valley floor, yes — mount the outdoor unit high enough that defrost meltwater and drifted snow don't refreeze into the base pan. Wall brackets or a proper stand beat a pad in any spot that holds snow. It's a cheap line item that prevents February coil damage.

Meaningfully. A sealed, conditioned crawl pulls duct into the envelope — condensation risk drops, R-requirements ease, and the system may need a small supply into the crawl per code. If the encapsulation crew got there before you, re-look at the duct plan instead of copying the old one.

Could be. Gas appliances derate with altitude — manufacturers spec it, commonly around 4% per 1,000 ft above a threshold — and some equipment wants a high-altitude kit or pressure adjustment. A 4,500-ft cabin isn't Denver, but it's not sea level either. Check the manual's altitude section before condemning the unit.