Help index
Search all topics — Electrical, RefCalc (every step), Air Flow, Sizing heat gain/loss, Save Log, license — as a compact bullet list.
Open help index & search topics →Refrigerant diagnostic formulas
Used in RefCalc steps 3 (Coil Airflow) and 4 (Duct Measurements).
Coil airflow (step 3)
- Evap TD (air) = Return DB − Evap discharge
- Evap discharge = Return DB − Evap TD
- Cond TD (air) = Cond discharge − ODB
- Cond discharge = ODB + Cond TD
- Evap TD (water) = Evap In − Evap Out
- Cond TD (water) = Cond Out − Cond In
Duct measurements (step 4)
- BTU/hr = CFM × 1.08 × ΔT
- CFM (sensible) = BTU/hr ÷ (1.08 × ΔT)
- VP = TP − SP (in. w.c.)
- FPM = 4005 × √VP
- CFM (sizing) = FPM × duct area (sq.ft.) — enter area in sq.in. (÷ 144 for sq.ft.)
- CFM (traverse) = FPM × duct area (from VP path)
Electrical calculators — how results are shown
Used in the merged Electrical tool (step menu: Power, Motor, VFD / Starters, 3-Phase, Compressor, Fan, Defrost, Load, Efficiency). Per-step topics: Help index.
Inputs vs outputs
- White / editable fields — nameplate or measured values (FLA, RLA, MCA, MOP on Motor; load amps, length, HP, etc.). Type here only.
- Plain-text results — calculated values in the same grid positions (wire size, drop %, kW, est. inrush, and Motor fields you did not type). Bold text only — not boxes — so they are not confused with inputs.
Live fill
- Results update when you leave a field or change a select (similar to RefCalc Coil Airflow fill).
- Calculate, CLR STEP, and CLR ALL still work from the bottom bar.
- Power step: last two of V / I / R / P / BTU you type are inputs; the rest that can be calculated update live. Length / phase / material only refresh voltage drop.
- Motor step: enter FLA, RLA, MCA, or MOP from the nameplate. FLA and RLA are the same running amps. Last typed values stay; others fill. Choose single- or three-phase (capacitors are 1φ only).
- Voltage drop: needs voltage, current, and one-way length (ft). Wire floor is load ÷ 0.8 then ≤ 3% drop (15 A → #12). Drop over 3% even at 4/0 marks length and drop % as Exceeds safety.
Breakers (running load only)
- MCA ≈ running amps × 1.25 (RLA or FLA — toggle on Compressor matches nameplate language; same math).
- Breaker / MOP = next standard size ≥ MCA. No 2.25× / 2.5× inrush on the breaker.
- Est. inrush (Compressor) ≈ running × 6 for a field ballpark. Display only — not used for breaker or wire. Prefer nameplate LRA when you have it.
Wire size (table)
- Copper size from a CEC-style ampacity table (Table 2 columns) plus small-conductor OCPD caps, then a continuous 80% of breaker floor (same as Power).
- Refrigeration-mechanic pairings: 15 A → 12 AWG (never #14), 20 A → 10 AWG, 30 A → 8 AWG when sized at breaker ÷ 0.8.
- Table 2 may list #14 at 20 A in the 75 °C column; this tool will not recommend #14 on a 15 A motor/breaker circuit.
First-visit disclaimer
- The first time you open Electrical on a device, a disclaimer explains field-guide limits, licence scope, and that full Code / AHJ rules are not applied. Full text is in Terms §3.1.
- Check Don't show again to store that choice in browser storage on this device.
Region (3-Phase step)
- NA | Europe toggles line-voltage lists and wye/delta presets (e.g. NA 240 / 347 / 600; 347 V = one leg of 600Y).
Remembered settings
- On this device, the tool stores region, system voltage, phase, wire material, RLA/FLA toggle, and other config dropdowns (not load amps or length). Returning to the page restores your last configuration.
Disclaimer: Field-reference only. Final wire, breaker, and installation design by a licensed electrician or professional engineer. These tools do not apply full CEC / NEC / IEC requirements and must not be used to work outside your licence. Terms §3.1.
Save Log
How the log panel and buttons work in RefCalc. Full topic →
When it appears
- The Save Log panel and Save PDF / Save Log / My Logs / Ask Grok buttons appear on output steps only (Key Metrics through Vapor & Performance).
- On input steps (Setup through Duct Measurements), use Run Diagnostic from the bottom action bar. That runs the diagnostic and moves you to the first output step.
File name
- Pre-filled with Report.YYYY-MM-DD (or your technician name from Settings). Tap the field to replace it.
- Later saves the same day get -2, -3 so Downloads does not overwrite. The file name is also the PDF header.
Action buttons
- Save PDF — download a PDF of the current diagnostic to your device. Requires a completed diagnostic.
- Save Log — upload the diagnostic PDF to your account (My Logs on the server). Requires a license and completed diagnostic.
- My Logs — open your saved diagnostic reports list.
- Ask Grok — builds a compact text summary (same data as the PDF report: inputs + readings like SH, SC, NRE) with the role prompt Refrigeration Engineer/Mechanic, 30+ years, copies it to your clipboard, and opens grok.com. On phones with the Grok app installed, the app often opens without the prompt pre-filled — paste into the chat if it is empty. In a desktop browser the prompt may auto-fill via the URL. Requires a Grok or X account.
- Save PDF, Save Log, and Ask Grok stay disabled until Run Diagnostic has completed successfully.
Refrigerant formulas for coil and duct input steps are in the formulas section above.
Air and oil: estimated oil temperature requires Discharge on the Setup step (unit follows °F/°C). Coil and gauge readings alone do not produce an oil estimate.
Temperature, pressure & airflow units
- On RefCalc Setup (and in Settings): toggle °F / °C and PSIG / PSIA / kPa (kPa is gauge).
- Applies to all RefCalc inputs and results; filled values convert when you switch. SH/SC/TD convert as deltas (no 32° offset).
- Calcs still use °F and PSIA internally. Full topic: Temperature & pressure units →
- Air volume: Air Flow step 1 shows CFM and L/s together (live aliases). Fan Laws, Settings, and RefCalc duct still toggle the display unit. All volume math uses CFM internally.
Reload last session
- Leaving a step or tool saves inputs into one shared file on this device (all calculators). Step changes merge — earlier steps are not wiped.
- A new app session starts blank. On home, use Reload last session to restore. Full topic →
License, login & this device
How free licenses, keys, and “remember this device” work. Full topic →
Free license requires an account
- Claiming a free license needs email + password (Supabase account) before the key is issued.
- We never show your license key to someone who only knows your email.
License does not expire
- Your HVAC Lens license does not expire — keep using your key on up to 5 devices.
- If the app asks you to refresh access (new device, cleared cache, or re-check online), use free renew:
License cache
- After unlock, the app stores a validated license in browser storage and cookies so the browser tab and home-icon PWA stay unlocked on the same profile.
- Clearing all site data (including cookies) or using a new browser profile removes this — unlock again with your key or email + password.
- The first time a new device is registered, you get a security email (not on every app open). Use the reset-password link if that was not you. Full topic →
Login session & cookies
- Login session — email + password via Supabase. Required to claim a free license and to recover a key after cache clear.
- Remember this device (cookie) — optional. Keeps your login on this browser so clearing cache alone does not always lock you out; the app can re-check online and restore your license without typing the key.
- License unlock also uses cookies (separate from the login session). Clearing “cached images and files” often leaves cookies; clearing “cookies and other site data” removes them.
When you must log in (or enter the key) again
- New browser, private/incognito window, or another device
- Cookies and site data cleared, or “Remove license from this device” in Settings
- License revoked, or all 5 device slots are full
Key vs password
- You can still unlock with the license key from your email (possession of the key).
- Password sign-in is the safe recover path when you do not have the key handy — never email alone.