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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017
1.2.12
Refrigerant shut-off valves
Shut-off valves with 2 switch statuses (open or closed)
♦ Shut-off valves come in different versions, with different func‐
tions and different designations ⇒ Heating, air conditioning;
Rep. gr. 87 ; Refrigerant circuit .
♦ If the shut-off valve -A- is not actuated by the electronics, it is
open and allows refrigerant to flow through.
♦ The shut-off valve -A- is installed on vehicles with high-voltage
system, for example. It is actuated when no climate control is
wanted for the passenger compartment but battery cooling is
required for the hybrid battery unit - AX1- .
♦ Note the arrow -B- on the shut-off valve -A-, which shows the
direction of refrigerant flow (from condenser to evaporator in
the heater and air conditioning unit).
♦ The solenoid -C- attached to the shut-off valve -A- is actuated
by different control units depending on the vehicle ⇒ Current
flow diagrams, Electrical fault finding and Fitting locations and
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -
air conditioning system and battery regulation.
♦ If, on a vehicle with 2 evaporators (one in the heater and air
conditioner unit and one in the battery cooling module, e.g. the
Audi Q5 Hybrid), the temperature measured at one evaporator
meets the specification or falls below the specification, while
on the other evaporator however the requisite specification is
not reached, regulation works as follows: the respective con‐
trol unit makes the electrical air conditioner compressor run at
a higher speed (which results in the cooling output of the air
conditioning system rising and pressure on the low pressure
side falling along with the evaporator temperature). If the tem‐
perature at an evaporator then falls below the specified level,
the respective control unit actuates the shut-off valve in such
lk
a way that the evaporator that is too cold no longer has refrig‐
erant flowing through it ⇒ Heating, air conditioning; Rep. gr.
87 ; Refrigerant circuit and ⇒ Vehicle diagnostic tester in “Gui‐
ded Fault Finding” mode.
Shut-off valves regulated via characteristic curves
♦ The shut-off valve -A- is actuated via an incremental motor
-B- by the respective control unit with characteristic curves
(open or closed).
♦ If the shut-off valve acts as a control valve (e.g. refrigerant
expansion valve 1 - N636- as is the case with the Audi Q7), it
is only opened enough to allow the temperature set for the heat
exchanger to be reached ⇒ Heating, air conditioning; Rep. gr.
87 ; Refrigerant circuit .
♦ Shut-off valves actuated via incremental motors do not have
a defined rest position. For this reason, they have to be set to
a certain position (open or closed) before work on the refrig‐
erant circuit is performed ⇒ Heating, air conditioning; Rep. gr.
87 ; Refrigerant circuit .
♦ Depending on layout of the refrigerant circuit there could be a
cluster of shut-off valves forming a valve block (e.g. on the e-
Golf or Audi Q7 e-tron) ⇒ Heating, air conditioning; Rep. gr.
87 ; Refrigerant circuit .
♦ The incremental motor is programmed and actuated via data
lines (LIN-Bus) by the respective control unit in relation to its
installation location ⇒ Heating, air conditioning; Rep. gr. 87 ;
Refrigerant circuit and ⇒ Vehicle diagnostic tester in “Guided
Fault Finding” mode.
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Rep. gr.87 - Air conditioning system
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