A/C System Overview
Features And Controls (MCC-ECC):
MCC stands for "Manual Climate Control". ECC stands for "Electronic Climate Control".
The climate control systems in the Volvo 850 have the following characteristics:
- Individual temperature control on driver and passenger sides.
- Availability of colder air from the center panel outlets by means of the air-mix control.
- 100% air recirculation facility.
- High ventilation capacity thanks to an efficient heater fan and large number of air outlets.
- High heating and cooling capacity.
- Stepless air distribution control.
- A/C system uses non-ozone depleting refrigerant.
MCC Control:
- The A/C and recirculation switches have indicator lights which come on when the functions are selected.
- Fan speed is controlled by a sliding control with four speed settings and an "off" position.
ECC control:
- The temperature controls are fitted with temperature scales and "max" and "min" settings.
- Automatic stepless control of fan speed with the fan speed control in the "aut" setting. Other settings give manual stepless control of fan speed, with an "off" position.
- Automatic air distribution control with the air distribution control in the "aut" setting. Other settings give manual stepless control.
- With the "rec" switch off (indicator light off), the ECC control unit will select recirculation in some cases if this will accelerate cooling.
- The "ac off" switch is used to switch the AC system off (indicator light off).
Distribution Ducts And Outlets (MCC-ECC):
Air is distributed uniformly throughout the passenger compartment via the following outlets:
- 7 windscreen defroster outlets
- 2 side defroster outlets
- 5 ventilation outlets
- 2 rear floor outlets
- 2 front floor outlets
- The windscreen defroster duct (1), in which air from the left- and right-hand sides is mixed, forms part of the instrument panel frame.
- There are separate side defroster ducts on the left- and right-hand sides (2 and 3). Since these conduct air directly from the heater, they can only deliver heated air.
- The left and right front floor ducts (5 and 6) are integral with the soundproofing panels.
- The air supply to the rear passengers first flows through a chamber (7) in which air from both sides is mixed. The flow is then divided between two ducts passing underneath the front seats.
- The left and right side ventilation ducts (4) are separate, and are generously dimensioned to handle a high airflow.
- The center ventilation outlets are also supplied by separate ducts (8).
Controls (MCC-ECC):
The same climate control unit is used in both the MCC and ECC systems. The image shows the control units and components used in each case. The ECC damper motors and MCC recirculation motors need no adjustment.
MCC:
- Fan resistance (1).
- Max. fan speed relay (2).
- A/C relay (13).
- The recirculation motor (3) controls the recirculation damper in three positions: open, closed or 30% recirculation at max. fan speed.
ECC:
- Damper motor, driver side (16).
- Damper motor passenger side (17).
- Damper motor, recirculation (18). Unlike the MCC recirculation motor; this has stepless control.
- Damper motor, ventilation (14).
- Damper motor, floor defroster (15).
- Power stage (11) controls fan (12) speed. As the power stage generates a certain amount of heat, the cooling fins face inwards towards the airflow.
- A/C relay (13).
Temperature Control (MCC-ECC):
Air to climate control unit. The fan draws in air to the climate control unit from outside or from the passenger compartment, depending on the position of the recirculation damper (1) and passes it through the evaporator (2). The airflow then splits into two through a baffle (3) before entering the heater (4).
Temperature Dampers. Two temperature dampers, one for the driver's side (5) and one for the passenger side (6), are controlled by cables in MCC systems and by damper motors in ECC systems. This can be used to give two airflows at different temperatures, depending on the temperature control settings.
Temperature Control. The temperature damper control setting governs how much air passes through the heater. With the damper in the center setting, half the air goes through the heater and half bypasses it. The hot and cold air are mixed after the temperature damper.
Air Distribution Dampers (MCC-ECC):
There are three pairs of air distribution dampers. The ventilation dampers (1) are mounted on the same spindle as the side defroster dampers (2), while the second spindle carries the floor/defroster dampers (3). The dampers are operated manually by cables from the air distribution control in MCC systems and by damper motors in ECC systems.
- The ventilation dampers (1) control the airflow to the ventilation outlets. More air is directed to the floor/defroster outlets as these are closed.
- The side defroster dampers (2) control the airflow to the left and right side defroster outlets.
- The floor/defroster dampers (3) control the air distribution between the defroster and floor outlets.
- Airflows:
- A Windscreen defroster.
- B Side defroster.
- C Center ventilation.
- D Side ventilation.
- E Rear floor.
- F Front floor.
When the ventilation dampers are closed, most of the air is directed through the floor/defroster dampers. A small quantity passes to the side ventilation outlets via the leak-off openings (4) and a further small quantity passes to the center ventilation outlets.
Ventilation Setting (MCC-ECC):
In the ventilation setting all air is directed to the ventilation outlets.
Damper settings:
- Ventilation dampers are fully open, shutting off the airflow to the floor/defroster dampers.
- Side defroster dampers closed.
- Floor/defroster damper center setting.
Defroster Setting (MCC-ECC):
In the defroster setting, around two-thirds of the air is directed upwards towards the windscreen, while the remainder is distributed between the side defroster and ventilation outlets.
ECC:
The recirculation damper is forced to assume the fresh air intake position even if the recirculation switch is on. The A/C is switched on (the A/C relay is activated) even if the A/C switch is off.
Damper setting:
- Ventilation dampers closed.
- Side defroster dampers open.
- Floor/defroster dampers in lower end position, shutting ducts to floor outlets off and directing air to the defroster outlets.
Floor/defroster Setting (MCC-ECC):
In the floor/defroster setting, about three-quarters of the air is distributed to the floor and windscreen defroster outlets. The remainder is distributed to the ventilation and side defroster outlets.
Damper setting:
- Ventilation dampers closed.
- Side defroster dampers open.
- Floor/defroster dampers in center setting.
Floor Setting (MCC-ECC):
In the floor setting, about three-fifths of the air is distributed to the front and rear floor outlets. A small amount of air is passed to the windscreen and the remainder is divided between the ventilation and side defroster outlets.
Damper setting:
- Ventilation dampers closed.
- Side defroster dampers open.
- Floor defroster dampers at upper limit, shutting the ducts to the defroster outlets and directing the air to the floor outlets.
Ventilation/floor Setting (MCC-ECC):
In the ventilation/floor (bi-level) setting, half the air is supplied to the floor outlets, approx. one-tenth to the side and windscreen defroster outlets and the remainder to the ventilation outlets.
The temperature of the air from the floor outlets will be somewhat higher than that from the ventilation outlets when the temperature control dampers are open. The lower part of the airflow through the ventilation dampers comes from the heater, so that air from the floor outlets is warmer than air from the ventilation outlets.
Damper setting:
- Ventilation dampers center setting.
- Side defroster dampers almost completely closed.
- Floor/defroster dampers near upper limits, directing most of the remaining airflow to the floor outlets.
Air-mix System (MCC-ECC):
The air-mix system enables fresh air to be supplied through the center ventilation outlets while heated air is obtained from the other outlets.
The system is made up as follows:
- Air-mix control (1).
- A duct (2) bypassing the heater and air distribution dampers.
- A damper (3) connected to the control by an adjustable link.
With the air distribution control in an intermediate setting between the defroster and floor settings, only a small quantity of treated air is supplied to the center ventilation outlets. This air will be mainly fresh if the air-mix damper is opened under these conditions. At other air distribution control settings, a mixture of treated and outside air will be supplied when the air-mix damper is opened.