Castair Float Switch for Low Oil Control — Replacement Sensor Component (Part# 6304B)
The Castair 6304B is the float switch sensor that is part of the 6304 low oil control system. If your low oil control unit is tripping or not detecting oil level correctly, and the wiring and control module check out, this float switch is the component to replace. It is the mechanical sensor — a float that rises and falls with crankcase oil level and triggers the protective switch when oil drops below the safe threshold.
At $40.81, the 6304B lets you replace the wear component of the low oil control system without replacing the entire assembly. That makes sense when the float or switch mechanism has failed but the mounting hardware and wiring are intact.
How the Low Oil Control System Works
The Castair low oil control system protects the compressor pump from running with insufficient lubrication. The system has two main components:
- The float switch (6304B — this part): A mechanical float that sits in the crankcase. As oil level drops, the float drops with it. At the trip point, the float activates a switch that signals the control circuit.
- The control module (6304 or 6304M): Receives the signal from the float switch and either triggers an alarm or cuts power to the motor, depending on configuration.
The 6304B is only the float switch — the sensor half of the system. It does not include the control module. If you need the complete system, see the 6304M (single unit, factory-mounted) or the 6304X2M (dual unit for duplex systems).
Specifications
- Part Number: 6304B
- Component: Float switch sensor (replacement component)
- Application: Castair 6304 series low oil control systems
- Function: Mechanical oil level detection, activates at low oil threshold
- Price: $40.81
When to Replace the Float Switch
- Float switch is physically damaged: The float itself can develop cracks or become waterlogged with oil over time, causing it to sink even when oil level is correct. This triggers nuisance low-oil shutdowns.
- Switch mechanism has failed open or closed: If the low oil control never trips when it should, or trips constantly when oil level is correct, the float switch mechanism is the first thing to test and replace.
- Preventive maintenance on high-hours compressors: On a compressor that has seen heavy use, replacing the float switch as part of a scheduled overhaul is inexpensive insurance.
- After a low-oil event: If the compressor actually ran low on oil, inspect the float switch. A float switch that was submerged in sludge or debris may not function reliably afterward.
Diagnosing Before You Order
Before ordering the 6304B, do a quick check of the full low oil control circuit:
- Verify oil level is actually correct — confirm with the dipstick, not just the sight glass if one is present.
- Check wiring from the float switch to the control module for damage, corrosion, or loose terminals.
- Disconnect the float switch and manually test continuity — with the float in the up position (normal oil level), the circuit should be in one state; with the float allowed to drop, it should switch.
- If continuity behaves correctly during bench test but the system still trips, the problem is in the control module or wiring, not the float switch.
If you are unsure how to test the float switch on your specific Castair model, call us at 866-217-0063 before ordering — we can walk through the diagnostic with you.
Parts Relationships — 6304 System Components
- 6304B (this part, $40.81): Float switch only — the sensor component
- 6304M ($147.95): Complete low oil control, single unit, factory-mount configuration
- 6304X2M ($296.25): Complete low oil control, dual unit, for duplex (two-pump) systems
Why the Low Oil Control System Matters
A Castair compressor pump is a significant investment. The C-series and G-series industrial pumps are all cast iron, oil-lubricated, and built for long service life — but only if they have adequate lubrication. Running a compressor pump dry, even briefly, can score the cylinder walls, damage the connecting rod bearings, and seize the crankshaft. A replacement pump costs far more than this float switch. The low oil control system is a cheap insurance policy against an expensive failure.
Why Buy From Air Compressor Factory Direct?
- Castair specialist: We carry the full 6304 system line — replacement float switches, complete single units, and duplex units.
- Free shipping on qualifying orders.
- Free technical support: Call 866-217-0063 if you need help diagnosing your low oil control system before ordering parts.
- OEM Castair components: The 6304B is a genuine Castair part — correct fit and function for 6304-series systems.
Call 866-217-0063 for quick answers and help!
