Compressor HVAC: Description and Operation

GF83.55-P-2108RT Component Description Of Refrigerant Compressor

Component Identification:

Location
The refrigerant compressor is connected to the engine at the front left.

Task
The refrigerant compressor is responsible for induction and compression of the refrigerant.

Component Identification:

Design
A total of 7 pistons are distributed around the circumference of the component and connected to the swash plate by sliding shoes to ensure the same pitch. The swash plate is connected to the stop plate in the crankcase by 2 guide pins and mounted on the refrigerant compressor shaft so that it can move.

The stop plate and belt pulley are stuck on the refrigerant compressor shaft. The externally-controlled refrigerant compressor control valve for adjustment of the swash plate is located in the rear section of the housing.

Function

Operating mechanism
The rotary movement of the belt pulley is transmitted over the refrigerant compressor shaft to the stop plate, which is permanently fastened to the refrigerant compressor shaft by way of a press fit. The rotation of the stop plate is then transmitted to the pivoted swash plate by means of a hinged mechanism. The conversion of the swash plate rotary motion into the oscillating piston movement takes place via two sliding shoes between the piston and swash plate. The 7 pistons are connected at the circumference with the swash plate with the same pitch. The evaporation tank on the pressure side and evaporation tank on the suction side reduce gas pulsation in the refrigerant compressor by providing for uniform refrigerant flow. This helps to prevent noises in the compression process

Volume regulation mechanism
The refrigerant compressor delivery rate is regulated by the externally-controlled refrigerant compressor control valve by the regulation flow between 2 % (minimum delivery rate) and 100 % (maximum delivery rate). The required control flow rate on the refrigerant compressor control valve is set by the AAC control and operating unit (N22) or comfort AAC control and operating unit (N22/7) depending on the required refrigeration capacity. The required refrigeration capacity is determined primarily by the vehicle interior temperature setting. The swash plate position and the variable delivery rate are always determined by the crankcase pressure, the membrane pressure in the refrigerant compressor control valve (approx. 2 bar) and the suction pressure. These pressures are determined on the basis of the sensing, processing and evaluation of the controlled variables in the air conditioning system.

The change in the suction pressure, depending on the control flow on the refrigerant compressor control valve, causes a change in the crankcase pressure and therefore, adjustment of the swash plate either in the direction of maximum delivery rate or variable delivery rate.

Automatic air conditioning OFF
When the automatic air conditioning is switched off with the A/C ON/OFF switch, the refrigerant compressor control valve is opened completely. This allows refrigerant to flow unimpeded from the high pressure side into the crankcase leading to an extremely rapid increase in the crankcase pressure. This causes the coil body for closing the refrigerant compressor to move to the right against the valve plate until the refrigerant flow is shut off completely on the suction side.

The coil body is designed such that at a delivery rate of 5 cm 3, the refrigerant flow is interrupted by closing off the intake passage, even when the refrigerant compressor is active.

Internal refrigerant compressor lubrication when air conditioning switched off
The refrigerant compressor has an internal lubricant circuit to ensure lubrication of the mechanical moving parts such as the sliding shoe, swash plate, front and rear radial shaft bearings, pistons and cylinder liner. Lubrication is ensured by way of a minimum refrigerant compressor delivery rate. This delivery rate is regulated by 2 valves. The minimum refrigerant compressor delivery rate of 2 % when the refrigerant compressor is switched off ensures that the refrigerant with the compressor oil present in the crankcase is transported through the bored refrigerant compressor shaft.

The mixture of refrigerant and refrigeration oil enters the crankcase on the intake side where it is compressed and then pumped into the refrigerant circuit on the pressure side. From the pressure side, the mixture of refrigerant and refrigeration oil flows back through a valve into the crankcase.

The refrigerant compressor output is regulated depending on the air humidity
The regulation of the refrigerant compressor output depends on the air humidity measured by the dew point sensor (B11/12). The air around the evaporator is no longer cooled down to approx. 3 °C, as previously, in order to then be heated back up to the desired temperature (Reheat mode). Reheat mode only takes place, if the reheat-associated air dehumidification effect is required to keep the windows condensation-free when humidity is high. Various regulations zones are differentiated depending on the relative air humidity.

Relative air humidity and operating condition
0 to 60 % No reheat mode
40 to 90 Reheat mode with variable temperature control between 0 and 12 °C
80 to 100% Full reheat mode

Outside air humidity
If the outside air is extremely moist, the refrigerant compressor operates at maximum capacity, i.e. the evaporator temperature is low (approx. 2 °C), for maximum air dehumidification. In heating mode, post heating is accordingly performed using the heat exchanger.

Dry outside air
With dry outside air the refrigerant compressor operates with reduced power output, i.e. the evaporator temperature can be up to approx. 14 °C, if no lower outlet air temperature becomes necessary.

The air humidity control is installed only on vehicles with comfort automatic air conditioning, code 581.