Carrier 7 PSI Radiator Cap — 30-60041-01 306004101 for Transicold Reefer Units

The Carrier 7 PSI radiator cap — OEM part numbers 30-60041-01, 306004101, 30-60041-00, 306004100, 30-60041-01SV, and 306004101SV — is a low-pressure cooling system pressure cap designed specifically for Carrier Transicold transport refrigeration units (reefer units) used on refrigerated containers, semi-trailers, and truck bodies. Unlike automotive and forklift radiator caps that are rated at 0.9-1.1 bar (13-16 PSI), the Carrier reefer unit cooling system operates at a significantly lower pressure of 7 PSI (approximately 0.48 bar). This low-pressure specification is critical: the reefer unit cooling system circulates coolant through a compact engine and radiator package where the radiator core, hose connections, and heater core (for defrost mode) are not designed to withstand the higher pressures of automotive cooling systems. Installing a standard 13 PSI automotive radiator cap on a Carrier reefer unit will over-pressurize the system, causing the weakest point — typically a plastic hose nipple, heater core end tank, or the radiator top tank seam — to rupture, dumping the entire coolant charge and disabling the reefer unit. A failed reefer unit on a container ship or refrigerated trailer means the cargo — pharmaceuticals, frozen food, or fresh produce worth thousands to millions of dollars — will spoil before the vessel reaches port.

This radiator cap is manufactured to OEM Carrier Transicold specifications with the correct 7 PSI pressure-relief spring calibration and the correct cap-to-neck sealing dimensions for Carrier TK-series, Ultra, and Vector reefer unit radiator filler necks. The cap uses a double-seal design: a spring-loaded pressure seal at the filler neck inner seat that opens at 7 PSI to vent excess pressure to the expansion tank, and a vacuum-relief valve in the cap center that opens under negative pressure when the engine cools down, allowing coolant to be drawn back from the expansion tank into the radiator — preventing radiator hose collapse from vacuum and maintaining a full coolant charge. The cap gasket is molded from EPDM rubber resistant to the ethylene glycol coolant mixture and the elevated under-hood temperatures of the reefer unit engine compartment, which can reach 80-90°C during continuous operation at rated load in tropical ambient conditions.

Direct OEM replacement for Carrier Transicold reefer units using the above part numbers. Cross-reference to Carrier service kits and aftermarket equivalents. For the complete Carrier cooling system including water pumps, thermostats, coolant hoses, and expansion tanks, browse our forklift radiator cap category. Always verify your existing cap pressure rating is 7 PSI before ordering — Carrier also uses 10 PSI and 15 PSI caps on different reefer unit models, and using the wrong pressure rating will cause either inadequate pressure (leading to coolant boiling and loss) or over-pressurization (leading to component rupture).

Technical Specifications

• OEM Part Numbers: 30-60041-01, 306004101, 30-60041-00, 306004100, 30-60041-01SV, 306004101SV
• Type: Low-pressure double-seal radiator cap
• Pressure Rating: 7 PSI (0.48 bar)
• Vacuum Relief: Integrated vacuum valve for coolant return from expansion tank
• Seal Design: Double-seal — pressure seal at inner neck + expansion tank seal
• Gasket Material: EPDM rubber, ethylene glycol and heat resistant
• Temperature Range: -40°C to +120°C continuous operation
• Application: Carrier Transicold TK, Ultra, Vector reefer units
• Quality: OEM-spec replacement

Compatible Carrier Transicold Reefer Units

Each radiator cap ships with the sealing gasket protected. Before installation, inspect the radiator filler neck sealing surface for pitting, corrosion, or debris — the 7 PSI seal relies on a perfectly smooth mating surface at the inner neck, and even minor pitting will prevent the cap from holding the rated pressure, allowing coolant to slowly boil off during operation. Press the cap onto the filler neck and rotate clockwise until the cap ears engage the neck ramps fully — the cap should require firm downward pressure during rotation as the spring compresses against the inner seal. After installation, pressure-test the cooling system to 10 PSI (the cap should vent at 7 PSI, so test pressure above the opening threshold verifies the cap is functioning). Never substitute an automotive radiator cap with a higher pressure rating “just to get the unit running” — the 7 PSI specification is not conservative; it is the maximum pressure the reefer unit cooling system components are designed to withstand, and exceeding it will cause a rupture that disables the reefer unit. For Carrier Transicold cooling system service procedures, consult Baldwin Filters. Kingstream stocks Carrier 7 PSI radiator caps for same-day dispatch — worldwide shipping with online tracking.