A stopped engine does not tell you whether the cabin is still being cooled. A blower moves air; a refrigerant compressor makes active cooling and dehumidification possible. Stored engine heat can provide warmth after shutdown without either being equivalent to refrigeration.
Three period Mercedes-Benz applications show the difference. Their operating states matter as much as their hardware: an operational hybrid with its engine temporarily paused is not a vehicle switched off for parking.
| Application | State | What the climate system provides |
|---|---|---|
| Pre-facelift 222 non-plug-in hybrid | Vehicle operational, READY lit; combustion engine automatically stopped | Electric compressor permits cooling and dehumidification, subject to energy and climate demand |
| Original C218 with three-zone THERMOTRONIC | Ignition off, REST active | Residual engine heat for heating; at high temperatures, ventilation only |
| Later pre-facelift non-hybrid W212 automatic with ECO | Automatic engine-stop phase | Reduced climate-control capacity; cabin temperature, windscreen moisture or battery charge can require an engine restart |
Hybrid READY: the compressor can keep working
The manufacturer’s 2015 222 manual describes an electric refrigerant compressor that can cool and dehumidify the cabin while the combustion engine is stopped. Its hybrid-specific climate instructions require the vehicle to be operational, with READY illuminated. Sources
In the separate non-plug-in HYBRID chapter, the high-voltage battery supplies energy for the compressor as well as supporting the 12 V onboard electrical system. The system overview identifies a high-voltage battery, a separate 12 V battery and power electronics with DC/AC or DC/DC conversion. The hybrid therefore retains two electrical systems; the high-voltage battery does not simply replace the 12 V battery. Sources
This gives the V222 S-Class hybrid a useful capability: a quiet combustion engine can coexist with actual refrigerated air, not merely a running fan. The manual describes maintaining the selected cabin temperature for a limited period after automatic engine shutdown. Climate demand can prevent the engine stopping or restart it; reaching the high-voltage battery’s lower charge limit can also restart it. Sources
Hong Kong offered the S400 Hybrid at the original 2013 launch. In this pre-facelift non-plug-in hybrid, READY remains a live operating state in which the engine can restart, distinct from parking with the ignition switched off. Sources
C218 REST: use the heat already there
The original C218 CLS manual limits its residual-heat function to THERMOTRONIC luxury three-zone automatic climate control. With the ignition off, REST can use heat remaining in the engine to warm the stationary cabin, with the blower running at low speed.
At high temperatures, the same function provides ventilation only, with medium blower speed. The manual separately states that cooling with air dehumidification requires the engine to be running. Air continuing to flow after shutdown therefore does not mean REST is refrigerating the cabin. Sources
Available heating time depends on the temperature setting and remaining heat; low battery voltage or insufficient coolant temperature can end operation. Sources
W212 ECO: comfort can call the engine back
For the later pre-facelift non-hybrid automatic W212, the 2012 manual says ECO stop/start requires the selected cabin temperature to have been reached, sufficient battery charge and an unmisted-windscreen condition when air-conditioning is on. During automatic engine stop, climate control operates at reduced capacity.
The engine can restart while the car is still stationary if cabin temperature moves outside the set range, moisture is detected on the windscreen with air-conditioning on, or battery charge becomes too low. A restart is therefore not controlled solely by the driver’s brake release. Sources
A December 2012 Hong Kong test records a 1.8-litre petrol E250 with seven-speed automatic transmission and ECO. The feature was therefore present on a locally offered W212 before the facelift. Sources
Sources
- Mercedes-Benz, S-Class Owner’s Manual, 2225842805Z102, Edition AEJ2015-2a, printed pp. 150, 153–154, 259–260, 267–268 / PDF pages +3: electric compressor, READY, non-plug-in HYBRID electrical supply and climate-related stop/restart conditions. The manual covers multiple models and optional equipment, with national variations.
- Car1, Mercedes-Benz 全新 S-Class 正式在港推出, 12 August 2013: Hong Kong S400 Hybrid offering; not a cooling-duration test.
- Mercedes-Benz, C218 Owner’s Manual, 2185840281Z102, printed pp. 110, 114, 118–119 / PDF pages +3: three-zone equipment scope, engine-running cooling requirement, residual heat and high-temperature ventilation. German-market operating documentation, including optional equipment.
- Mercedes-Benz, W212 Owner’s Manual, 2125847981Z102, 2012, printed pp. 166–167 / PDF pp. 169–170: ECO prerequisites, reduced climate capacity and automatic-transmission restart conditions. German-market operating documentation; hybrids have separate instructions.
- Oriental Daily, 平治E250 要豪亦講慳, 12 December 2012: Hong Kong four-door automatic petrol E250 test explicitly identifying ECO equipment.