Castair Hour Meter — 24 to 277 Volt with Varistor (HRM75)
The HRM75 is the standard electric-motor hour meter in Castair's lineup, designed to track operating hours on air compressors running anywhere from 24 to 277 volts. This is the meter Castair lists on their accessories page for general compressor installations, priced at 58.44. It connects directly to the motor circuit and accumulates hours only when the motor is actually running — so it gives you an accurate count of actual pump operating hours, not wall-clock time. That number is what drives your oil change schedule, pump maintenance intervals, and valve service timing.
The varistor included with the HRM75 provides overvoltage transient protection — when the motor circuit switches, it generates voltage spikes that can damage unprotected electronics. The varistor absorbs those spikes and protects the meter's internal counter mechanism from premature failure.
Why Put an Hour Meter on a Compressor?
Castair specifies oil changes at 400 hours (semi-synthetic) or 800 hours (full synthetic). Valve service, belt inspection, and bearing checks also run on hour-based intervals. Without an hour meter, you are guessing — and most shops either change oil too frequently (wasted money) or not frequently enough (worn valves, oil degradation). The HRM75 removes the guesswork. One meter. One number. Change oil when it hits 800. Service valves when it hits the manufacturer's interval. Period.
It also gives you immediate diagnostic feedback. If your HRM75 shows 4,200 hours and the compressor has never had a valve job, that tells you something. If you are selling a used compressor, hour meter reading is the single most credible data point for a buyer.
HRM75 Features
- Wide Voltage Range: 24 to 277 volts AC/DC — covers virtually all single-phase compressor installations (120V, 230V, 240V) without needing a separate voltage-matched meter
- Varistor Included: Transient voltage suppressor protects the meter from motor-switching voltage spikes — a common cause of premature hour meter failure
- Counts Running Hours Only: Meter advances only when powered — counts actual compressor operating hours, not elapsed calendar time
- Non-Resettable Counter: Hours accumulate permanently — useful for maintenance tracking and resale documentation
- Castair Factory Listed: This is the meter Castair specifies for standard electric compressor installations in their accessories catalog
- Compact Size: Designed for panel mounting on compressor control boxes and enclosures
HRM75 vs. HRM460 — Which Meter Do You Need?
Castair offers two electric compressor hour meters. The distinction is voltage:
- HRM75 (24-277V) — THIS PRODUCT: For virtually all single-phase compressors — 120V, 208V, 230V, 240V. Also works on 24V control circuits. Use this for standard shop compressors running on single-phase power.
- HRM460 (460V): For three-phase compressors running on 460-volt power. A standard 277-volt-max meter will be destroyed by 460V — you must use the HRM460 on 460V three-phase installations.
- HRM50 (Gas Engine): For gasoline-engine-powered compressors. Connects to the ignition circuit rather than an AC motor circuit.
Factory Mounting Options
Castair offers factory-mounted versions of this meter for new compressor installations:
- HRM75M (230 volt) — Factory-mounted version, ordered as an option on new Castair compressors. Same meter, pre-wired and panel-mounted at the factory.
- HRM75x2M — Factory-mounted duplex version for dual-compressor alternating systems (two meters for two compressors).
What's in the Box
- 1 x Hour meter (HRM75)
- 1 x Varistor (overvoltage protection)
Technical Specifications
- Part Number: HRM75
- Voltage Range: 24 to 277 VAC/VDC
- Application: Single-phase electric motor compressors (120V, 208V, 230V, 240V)
- Varistor: Included
- Counter Type: Non-resettable hour accumulator
- Mount: Panel mount
- Castair Part Number: HRM75
Why Buy From Air Compressor Factory Direct?
We have specialized in Castair compressors and accessories since 2016. The HRM75 is a direct Castair factory part — same meter Castair installs on their own compressors. Installing an hour meter is one of the highest-value maintenance investments you can make on a compressor: it costs less than one oil change and eliminates guesswork for every maintenance interval going forward. Free shipping, free tech support at 866-217-0063, full warranty.
Call 866-217-0063 for quick answers and help!
