Volkswagen Polo Service & Repair Manual: Checking with Expansion Valve, Receiver/Dryer and A/C Compressor Regulator
Valve -N280-, Externally Regulated A/C Compressor
 Note
| Connecting service station. Refer to
→ Chapter „Connecting Service Station“. |
| Observe test requirements. Refer to
→ Chapter „Pressures, Checking“. |
| – |
Bring engine speed up to 2000 RPM. |
| – |
Pay attention to the A/C service station pressure gauge. |
Note
| Switching pressures for actuation of A/C Compressor
Regulator Valve -N280- and Coolant Fan -V7- are
vehicle-specific. |
| The pressures should be measured at the service connections.
The location of these connections is vehicle-specific. Refer to
→ Rep. Gr.87. |
| Increasing from initial pressure (when connecting pressure
gauges) to 20 bar (290 psi). |
|
|
|
| Decreasing from initial pressure (when connecting pressure
gauges) to the value in the graph. |
| A - |
Low pressure (measured at service connection) in bar (psi)
absolute |
| B - |
Control current for A/C Compressor Regulator Valve -N280-. |
| C - |
Permissible tolerance range |
Note
| Under unfavorable conditions (very high ambient
temperatures, high humidity), pressure on high-pressure side may
increase to max. 29 bar (421 psi). |
| The control current -B- is
shown in the measured value block. |
| The high pressure measured from the High Pressure Sensor
-G65- is not shown in the measured value block. Refer to
→ Rep. Gr.87. |
| Low pressure settles as a function of control current for
A/C Compressor Regulator Valve -N280- within compressor output
range in tolerance range. |
| Under unfavorable conditions (very high ambient
temperatures, high humidity), compressor output may not always
be sufficient to attain the specified value. |
| The specified operating current for the regulator valve must
be greater than 0.3 A in order to ensure reliable valve
activation. |
| In the setting “maximum cooling output” control current is
regulated to approximately 0.65 A up to 0.8 A (vehicle specific,
displayed in measured value block). Refer to
→ Rep. Gr.87. |
| At absolute pressure, 0 bar/psi corresponds to absolute
vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi)
absolute pressure. 0 bar/psi pressure corresponds to an absolute
pressure of 1 bar (14.5 psi) on most pressure gauges (indicated
by 1 bar (14.5 psi) below 0 bar/psi). |
|
|
|
|
Possible deviation from specification |
Possible cause of fault |
Corrective
action |
| High pressure remains constant or increases only slightly
(above pressure with engine stopped). |
| Low pressure quickly drops to value in graph or below. |
| Required cooling output is not attained |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
| Not enough refrigerant in refrigerant circuit |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
| – |
Localize the leak with leak detector and eliminate |
| – |
Charge the refrigerant circuit. |
|
| Low pressure in line with value in graph. |
| Required cooling output is not attained |
|
|
|
| Low pressure too low (see graph). |
| Required cooling output is not attained |
|
| Not enough refrigerant in refrigerant circuit |
|
| – |
Extract refrigerant from the refrigerant circuit |
| If quantity of refrigerant extracted is substantially less
than specified capacity. |
| – |
Localize leak with leak detector and eliminate. |
| – |
Charge the refrigerant circuit. |
| If quantity of refrigerant extracted roughly corresponds to
specified capacity: |
|
| |
|
| – |
Replace expansion valve |
| – |
Charge the refrigerant circuit. |
|
Note
| If no malfunction is found with this complaint, flush
(clean) refrigerant circuit with refrigerant R134a. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. If that is not possible in this
workshop, flush the refrigerant circuit with compressed air and
remove moisture with nitrogen. Refer to
→ Chapter „Refrigerant Circuit, Flushing with Compressed Air and
Nitrogen“. |
| Check measured values from Evaporator Vent Temperature
Sensor -G263- or Evaporator Temperature Sensor -G308- and
activation of A/C Compressor Regulator Valve -N280-. If the
measured value of the Evaporator Vent Temperature Sensor -G263-
or Evaporator Temperature Sensor -G308- is not OK, the
evaporator can ice up or the cooling output will not be reached. |
| If the function of the air conditioning system is not OK
when the test is repeated after replacing expansion valve,
re-install old expansion valve and flush refrigerant circuit
with compressed air and nitrogen. Then replace A/C compressor
and receiver/dryer. |
| With this malfunction, evaporator may ice up although
quantity of refrigerant in circuit is OK. |
| If expansion valve is malfunctioning (permanently closed or
does not open sufficiently), A/C Compressor Regulator Valve
-N280- is actuated to maximum output and low pressure drops to
value in graph or below (compressor draws off refrigerant from
low-pressure side). Because refrigerant cannot flow through the
expansion valve, the correct cooling output cannot be reached.
The high pressure may not increase or may only increase
slightly. |
|
|
|
|
Possible deviation from specification |
Possible cause of fault |
Corrective
action |
| High pressure only increases slightly above pressure with
engine stopped. |
| Low pressure drops only slightly. |
| Required cooling output is not attained |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
|
| |
|
| – |
Extract refrigerant circuit. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Replace A/C compressor. |
| – |
Charge the refrigerant circuit. |
|
| High pressure increases above specification. |
| Low pressure quickly drops to value in graph or below. |
| Required cooling output is not attained |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
|
| |
| Constriction or obstruction in refrigerant circuit |
|
| – |
Run hand over refrigerant circuit to check for differences
in temperature |
| If difference in temperature is found at one component: |
| – |
Replace the hose or pipe if kinked or constricted. |
| – |
In the event of an obstruction, flush refrigerant circuit
with compressed air and nitrogen |
| – |
Charge the refrigerant circuit. |
| If no malfunction can be found: |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Charge the refrigerant circuit. |
| – |
Repeat test if function is not OK. |
|
| |
|
| – |
Extract refrigerant circuit. |
| – |
Replace expansion valve and receiver/dryer |
| – |
Charge the refrigerant circuit. |
|
Note
| With this malfunction, evaporator may ice up although
quantity of refrigerant in circuit is OK. |
| If expansion valve is malfunctioning (permanently closed or
does not open sufficiently), A/C Compressor Regulator Valve
-N280- is actuated to maximum output and low pressure drops to
value in graph or below (compressor draws off refrigerant from
low-pressure side). Because refrigerant cannot flow through the
expansion valve, the correct cooling output cannot be reached.
The high pressure may not increase or may only increase
slightly. |
|
|
|
|
Possible deviation from specification |
Possible cause of fault |
Corrective
action |
| High and low pressure normal at first, after some time high
pressure increases above specification. |
| after some time, low pressure decreases to graph value or
lower. |
| Required cooling output is no longer attained. |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
|
| High pressure and lower pressure normal first, after a long
period of driving, the low pressure falls below the specified
value (evaporator iced up). |
|
| Moisture in refrigerant circuit |
|
| – |
Extract refrigerant circuit. |
| – |
Flush refrigerant circuit with compressed air and nitrogen. |
| – |
Replace receiver/dryer with dryer. |
| – |
Evacuate refrigerant circuit for at least 3 hours. |
| – |
Charge the refrigerant circuit. |
| – |
Repeat test, if function is not OK. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Charge the refrigerant circuit. |
|
Note
| If this complaint occurs after a long operating time or only
sporadically (the low pressure falls under the specified value
and the evaporator ices up), replacing the dryer (installed in
the receiver/dryer) is sufficient. The quantity of refrigerant
oil should be adjusted. Refrigerant circuit is then to be
evacuated for at least 3 hours. |
| First, it is not necessary to flush the refrigerant circuit
with compressed air and nitrogen in case of this complaint
because generally only a small amount of moisture is in the
system and this can be removed by a long evacuation. |
| With this malfunction, evaporator may ice up although
quantity of refrigerant in circuit is OK. |
|
|
|
|
Possible deviation from specification |
Possible cause of fault |
Corrective
action |
| High pressure normal, low pressure too low (see graph), the
necessary cooling output is not reached. |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
|
| |
|
| – |
Extract refrigerant circuit. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Replace expansion valve and receiver/dryer |
| – |
Charge the refrigerant circuit. |
| – |
Repeat test if function is not OK. |
| – |
Replace the A/C compressor. |
|
| |
|
| – |
Extract refrigerant circuit. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Replace the A/C compressor. |
| – |
Charge the refrigerant circuit. |
|
Note
| For the malfunction “high pressure normal, low pressure too
low”, note the following: faulty, the evaporator can ice up or
the cooling output is not reached. |
| With this malfunction, evaporator may ice up although
quantity of refrigerant in circuit is OK. |
| Check measured values from Evaporator Vent Temperature
Sensor -G263- or Evaporator Temperature Sensor -G308- and
activation of A/C Compressor Regulator Valve -N280-. If the
measured value of the High Pressure Sensor -G65- is faulty, the
evaporator can ice up or the cooling output is not reached. |
| If the problem is with the A/C Compressor Regulator Valve
-N280- (regulating valve is not actuated but compressor operates
nevertheless), refrigerant circuit does not have to be flushed.
With this malfunction, replacing the A/C compressor is
sufficient (adjust refrigerant oil quantity in new A/C
compressor). |
| If expansion valve is malfunctioning (permanently closed or
does not open sufficiently), A/C Compressor Regulator Valve
-N280- is actuated to maximum output and low pressure drops to
value in graph or below (compressor draws off refrigerant from
low-pressure side). Because refrigerant cannot flow through the
expansion valve, the correct cooling output cannot be reached.
The high pressure may not increase or may only increase
slightly. |
|
|
|
|
Possible deviation from specification |
Possible cause of fault |
Corrective
action |
| High pressure normal or too high. |
| Low pressure too high (see graph). |
| A/C compressor noise (particularly after switch-on). |
| Required cooling output is not attained |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
| Too much refrigerant in the circuit. |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
| – |
Extract refrigerant from the refrigerant circuit |
| If quantity of refrigerant extracted roughly corresponds to
specified capacity: |
| – |
Replace the A/C compressor. |
| If quantity of refrigerant extracted is substantially
greater than specified capacity: |
| – |
Charge the refrigerant circuit. |
|
| |
| To much refrigerant oil in the circuit. |
|
| – |
Discharge the refrigerant circuit. |
| If quantity of refrigerant extracted roughly corresponds to
specified capacity: |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Charge the refrigerant circuit. |
|
| |
|
| – |
Discharge the refrigerant circuit. |
| – |
Replace expansion valve and receiver/dryer |
| – |
Charge the refrigerant circuit. |
| – |
Repeat test if function is not OK. |
| – |
Replace the A/C compressor. |
|
| |
|
| – |
Discharge the refrigerant circuit. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Replace the A/C compressor. |
| If quantity of refrigerant extracted is substantially
greater than specified capacity: |
| – |
Charge the refrigerant circuit. |
|
Note
| If the problem is with the A/C Compressor Regulator Valve -N280-
(regulating valve is not actuated but compressor operates nevertheless),
refrigerant circuit does not have to be flushed. With this malfunction,
replacing the A/C compressor is sufficient (adjust refrigerant oil
quantity in new A/C compressor). |
| Overfilling with refrigerant oil can occur if, for example, the
compressor has been replaced without adjusting the quantity of
refrigerant oil. |
| If the A/C compressor is not replaced, the refrigerant oil should be
drained from the A/C compressor via the oil drain plug. Out of the
entire quantity of refrigerant oil, 50 grams should be put in the A/C
compressor and the rest in the refrigerant circuit. Refer to
vehicle-specific repair manual. |
| If expansion valve is malfunctioning (permanently closed or does not
open sufficiently), A/C Compressor Regulator Valve -N280- is actuated to
maximum output and low pressure drops to value in graph or below
(compressor draws off refrigerant from low-pressure side). Because
refrigerant cannot flow through the expansion valve, the correct cooling
output cannot be reached. The high pressure may not increase or may only
increase slightly. |
|
Possible deviation from specification |
Possible cause of fault |
Corrective
action |
| High and low pressure normal. |
| Required cooling output is not attained |
|
| Activation of A/C Compressor Regulator Valve -N280- is
faulty. |
| To much refrigerant oil in the circuit. |
|
| – |
Check activation of A/C Compressor Regulator Valve -N280-. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
|
| High and low pressure normal. |
| A/C compressor noise (particularly after switch-on). |
| The required cooling performance is obtained |
|
| To much refrigerant oil in the circuit. |
|
| – |
Discharge the refrigerant circuit. |
| – |
Flush (clean) refrigerant circuit. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“. |
| – |
Charge the refrigerant circuit. |
|
| |
|
| – |
Replace expansion valve |
|
Note
| Overfilling with refrigerant oil can occur if, for example, the
compressor has been replaced without adjusting the quantity of
refrigerant oil. |
| If the A/C compressor is not replaced, the refrigerant oil should be
drained from the A/C compressor via the oil drain plug. Out of the
entire quantity of refrigerant oil, 50 grams should be put in the A/C
compressor and the rest in the refrigerant circuit. Refer to
vehicle-specific repair manual. |
| If expansion valve is malfunctioning (permanently open), evaporator
temperature is no longer regulated such that only refrigerant in gaseous
state exits from the evaporator. Under certain usage conditions, liquid
droplets may then be drawn in by the compressor and cause noise (liquid
cannot be compressed). |
With Expansion Valve, Receiver/Dryer and Electrically-Driven A/C
Compressor
Note
| The electrically-driven A/C compressor does not have an A/C
Compressor Regulator Valve -N280-. The A/C compressor RPM does
the regulating. The A/C compressor contains the control
electronics and a G-charger, which moves the refrigerant. |
|
Note
Connecting service station. Refer to
→ Chapter „Connecting Service Station“.
Observe test requirements ...
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The Wiring Harness Repair Set - Wire Strippers -VAS1978/3-
is used for professional stripping and cutting of wires.
The Wiring Harness Repair Set - Wire Strippers -VAS1978/3-
is a component of the Wiring Harness Repair Set -VAS1978B- and
...
Silicone Remover
Definition:
Silicone Remover -LSW 019 000 A5-, watery
Silicone Remover -LVM 020 000 A5-
Silicone Remover, Long -LVM 020 100 A5-
Edition 02/2012
S ...
A/C Pressure/Temperature Sensor -G395
Note
For switching pressures, removing and installing switches
and switch arrangement and version, see vehicle-specific
refrigerant circuit.
Refer to
→ Rep. Gr.87.
...
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Checking with Restrictor, Reservoir and A/C Compressor Regulator Valve
-N280-, Externally Regulated A/C Compressor