Checking Cooling Output of Air Conditioner
Checking Cooling Output Of Air Conditioner
Special tools, testers and other items required
- Diagnostic Operation System VAS 5051A (or Vehicle Diagnosis and Service System VAS 5052)
- Commercially available thermometer (for temperature measurement; if applicable use thermometer with 2 probes for simultaneous measurement of temperature e.g. on right and left)
Test Requirements
- Ambient temperature above 15 degrees C
- Radiator and condenser clean (clean if necessary)
- Poly V-belt for compressor drive OK and correctly tensioned, pulley actually driving compressor
- All air ducts, covers and seals OK and properly installed
- Air flow through dust and pollen filter not impeded by contamination
- Vehicle not exposed to sunlight
- Engine warm
- DTC memory of Climatronic Control Module J255 (Rear A/C Control Head (Climatronic) E265) checked and erased, basic setting performed and coding of Climatronic Control Module J255 checked Reading and Clearing Diagnostic Trouble Codes and "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051
- Adaptation of Climatronic Control Module J255 (and Rear A/C Control Head (Climatronic) E265) checked Adaptation (Function 10) "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051
- All dash panel vents open
- Hood closed
- Settings on Climatronic Control Module J255 or on MMI (Multi Media Interface):
- "Auto" mode
- "LO" temperature setting (for drivers and front passengers side)
- Compressor on ("Econ" function not active in MMI)
- Functions with engine running:
- Operation of Coolant Fan V7 (speed governed by pressure in refrigerant circuit and engine temperature)
- Operation of Fresh Air Blower V2 at maximum speed
- Switching of air conditioner to recirculation mode (approx. 1 minute after starting vehicle, fresh-air/air flow flaps are closed and recirculation flap opened, air is drawn in by Fresh Air Blower V2 from passenger compartment beneath dash panel)
- No operation of Coolant Pump V50
- Left Heat Regulating Valve N175 and Right Heat Regulating Valve N176 closed (coolant hoses/coolant pipes to heating system heater cores cool down)
NOTE: If one of these test requirements is not satisfied, check DTC memory of Climatronic Control Module J255, perform final control diagnosis and read out measured value block (display groups "001" and "002") "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051.
Checking
- Measure ambient temperature (must be above 15 degrees C).
- Close doors, hood, windows and sun roof.
- Open all dash panel vents.
- Switch on ignition.
- Set "Econ" mode on MMI.
- Close vents in "B" pillar.
- Set handwheel for variable temperature center vent to "Warm".
- Start engine.
- Start air conditioner self-diagnosis "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051 .
- In Climatronic Control Module J255 select function "Reading measured value block" display group "001" "Guided Fault- Finding" function of Diagnostic Operation System VAS 5051.
- Check display in display zones:
- Display zone "2" shows 0% (compressor off).
- Display zone "4" indicates that pressure in refrigerant circuit at measured ambient temperature is equal to or greater than value in table.
Ambient temperature in degrees C Pressure display (in bar absolute)
15 4.7
20 5.6
25 6.6
30 7.6
35 8.8
NOTE: At absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly 1 bar absolute. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar (can be seen from -1 mark below 0). Pressure in refrigerant circuit is governed by ambient temperature. Due to heat emitted by components (e.g. radiator), pressure displayed with warm engine is slightly higher than that indicated for the relevant ambient temperature. If pressure displayed is lower than that given in the table: Check signal of air conditioner High Pressure Sensor G65. Testing and Inspection If no malfunction is found with air conditioner High Pressure Sensor G65, the refrigerant charge is low.
If pressure in refrigerant circuit is OK:
- Switch on compressor by selecting "Auto" mode on Climatronic Control Module J255 or on MMI (Multi Media Interface).
- Select "Lo" temperature (for drivers and front passengers side) on Climatronic Control Module J255.
- Set air outflow direction on Climatronic Control Module J255 to "dash panel vents".
- Select display group "001" in "Reading measured value block" function "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051.
- Check display in display zones:
Display zone "2" shows a duty cycle of greater than 30 percent (actuation of A/C Compressor Regulator Valve N280, compressor is switched on).
Display zone "1" shows a current of greater than 0.3 A (current flowing via A/C Compressor Regulator Valve N280, compressor is switched on).
Pressure displayed in zone "4" rises above value when compressor is switched off.
- Check measured value of Evaporator Vent Temperature Sensor G263 ("Reading measured value block" function, display group "018") "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051.
- If sender measured value is too high under usage conditions described by customer (greater than e.g. 10 degrees C although air conditioner is functioning properly), check Evaporator Vent Temperature Sensor G263 (incorrect measured value can cause evaporator to ice up).
NOTE: A/C Compressor Regulator Valve N280 is actuated by Climatronic Control Module J255 such that temperature of air downstream of evaporator reaches specified value (approx. 2 to 5 degrees C): After starting vehicle, value greater than 75 percent (0.55A) is displayed depending on measured temperature, engine speed and electrical system voltage. As soon as temperature measured by Evaporator Vent Temperature Sensor G263 approaches specified value, actuation is cancelled and compressor output thus reduced. Connectors to A/C Compressor Regulator Valve N280 and electric engine mounting are identical. If connectors are interchanged (possible for example on vehicles with 4.2 l engine), no entry is made in DTC memory, but compressor is constantly actuated and evaporator may ice up. Under certain operating conditions, residual moisture in the coolant circuit may lead to the formation of ice at the compressor regulating valve. Such ice formation impairs compressor control, the evaporator is cooled excessively and ices up. Icing-up of evaporator may give rise to the following problems: - Repeated or sporadic failure of air conditioner (no cooling/heat output) after a long journey; air conditioner functions properly again after a short delay following engine shutoff. - Misting up of windows on inside after a long journey; windows are initially not cleared even by pressing "Defrost" button; air conditioner functions properly again after a short delay following engine shutoff.
If sender measured value is too low under usage conditions described by customer (colder than 0 degree C for lengthy period at ambient temperature above 0 degree C), proceed as follows:
Check refrigerant pipe between evaporator and accumulator (thick pipe, low-pressure end) with engine running. If this pipe is severely iced up when problem occurs (thin layer of ice is permissible), this also indicates that evaporator temperature is too low.
If display zone "1" shows no or insufficient current, check actuation of A/C Compressor Regulator Valve N280.
If pressure indicated in display zone "4" does not change and compressor actuation is OK (display zones "1" and "2"), there is a malfunction in the refrigerant circuit. Refer to Air conditioner with refrigerant R134a.
- Press recirculation mode button on Climatronic Control Module J255 (symbol for "recirculation mode" in button lights).
- Set engine speed to 2000 rpm (start of time measurement).
- In "Reading measured value block" function, select display group "018" "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051.
- Compare measured value indicated in display zone "1" (for Evaporator Vent Temperature Sensor G263) to values in graph.
A. - Air temperature measured by Evaporator Vent Temperature Sensor G263
B. - Ambient temperature
C. - Permissible tolerance range
Depending on ambient temperature, measured air temperature must be within the stated tolerance range after 5 minutes.
NOTE: If required values are not attained, check measured value of Evaporator Vent Temperature Sensor G263. Compare measured values shown in display groups "018", zone "1" and "017", zones "1" and "2": If measured value in the two display zones "1" or "2" in display group "017" only differs slightly from that in display group "018": Perform "Measures to be taken if readout does not match specification".Measures to Be Taken If Readout Does Not Match Specification If measured value of Evaporator Vent Temperature Sensor G263 is higher than that of Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151, check proper installation of Evaporator Vent Temperature Sensor G263 and perform electrical check for this sender and installing and "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051. Operation of air conditioner can be established, for example, from cooling down of refrigerant pipe on low pressure end (thick pipe).
If measured value of Evaporator Vent Temperature Sensor G263 (and thus system cooling output) is OK:
- Compare measured value indicated in zone "1" of display group "018" (for Evaporator Vent Temperature Sensor G263) to measured values of display group "017", zones "1" and "2" (Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151).
- After 5 minutes, measured values in display group "017", zones "1" and "2" (Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151) must not be more than 3 degrees C higher than value in zone "1" of display group "018" (for Evaporator Vent Temperature Sensor G263).
NOTE: If required values are not attained, compare measured values indicated in display group "017", zones "1" and "2": - If measured value is OK in one of the two display zones "1" or "2", check actuation and operation of Left Heat Regulating Valve N175, Right Heat Regulating Valve N176 and Coolant Pump V50 and "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051. - If measured value in zone "1" or "2" of display group "017" is lower than that in zone "1" of display group "018", check Evaporator Vent Temperature Sensor G263, Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151 for proper installation and contact resistance at electrical connections and replace faulty sender if necessary "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051. - If no DTC is found at Left Vent Temperature Sensor G150, Right Vent Temperature Sensor G151, Left Heat Regulating Valve N175, Right Heat Regulating Valve N176 and Coolant Pump V50, perform measures to be taken in the event of temperature increase downstream of evaporator. Temperature of air flow from "Center" dash panel vents can additionally be measured for example using a commercially available thermometer. If air flowing out of variable temperature center vent (in "Lo" setting for drivers and front passengers side on Climatronic Control Module J255) is cooled in "Cold" setting and not cooled in "Warm" setting, check operation of Left Heat Regulating Valve N175 and Right Heat Regulating Valve N176 "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051. If cooling output on front passengers side is still adequate, but values are no longer attained on drivers side, this is an indication of insufficient refrigerant in refrigerant circuit (stratification in evaporator due to lack of refrigerant). Problems relating to differences between temperature of air emitted by vents with identical setting in air conditioner control mode may be due to the following: - Cold or warm air flaps in air ducts not closing fully or not attaining end position Air intake and air routing in air conditioner unit and "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051 - Air in one or both heater cores (different flow through heater cores and uneven heat distribution) - Detachment of foam seal on heater core installation, allowing air to flow past heater core