0100 YRM 1459
MCC Heater and Air Conditioner
MCC Heater and Air Conditioner HEATER SYSTEM General Lift trucks with a closed cab are equipped with a heater assembly which is installed on the underside of the cab. The main components of the heater assembly are the fan, heater core, vent door, and an evaporator for the optional air conditioning system. See Figure 1.
Cabs that are equipped with an air conditioner have an electrically controlled vent door that can be used to vary the percentage of recirculated air between 0 and 100 percent. The operator can select the position of the vent door by turning a knob on the dashboard. Cooling performance increases by reducing the percentage of incoming fresh air. Recirculated air enters the heater assembly through the openings in the side console at the fuse cover. Fresh air enters the heater assembly through the cab air filter, which is located at the left rear corner of the cab. As the filter becomes restricted or clogged, the percentage of recirculated air will increase and the percentage of fresh air will decrease. When fresh air content and fan speed is increased, positive air pressure is created in the cab, preventing dust from entering the cab. The air pressure escapes through the cab door posts and through openings in the pedal area and sliding window brush profiles.
A. RECIRCULATED AIR B. FRESH AIR ENTRY C. CAB AIR FLOW 1. 2. 3. 4. 5. 6. 7. 8.
VENT DOOR VENT DOOR ACTUATOR EVAPORATOR CORE HEATER CORE BLOWER THERMOSTAT WATER VALVE EXPANSION VALVE Figure 1. Heater/Airco Assembly Components
The vent door determines the percentage of fresh air and recirculated air that the fan pulls through the heater assembly. In heater assemblies without an air conditioner, the vent door is in a fixed position and allows for an air mixture of 85% fresh air and 15% recirculated air.
When the fan is switched ON, air is pushed through channels in the cab floor to the air ducts at the front window. Cabs that are equipped with an air conditioner have three additional vents at the foot area that can be opened or closed. Cooling capacity is increased by opening the three vents. When the three vents are open, air flow is less restricted, increased air volume passes through the evaporator, and the majority of the air no longer becomes warm in the air channels that lead to the front window. See Figure 2. The heater consists of a heater core and a water valve. See Figure 1. The water valve controls the flow of heated coolant to the heater core. By varying the opening of the water valve, the desired amount of heat is transferred by the heater core to the air that enters the cab. The water valve opens proportionally to the selected position of the heat control knob. On standard units the knob and valve are connected mechanically, on units with an Air Conditioning system there is an electronic connection.
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