1988 Mercedes Benz 300sd Blower Resistor

  • 1988 MERCEDES BENZ 300SD
Air Conditioning problem
1988 Mercedes Benz 300sd 6 cyl Automatic

where can I look for the airconditioner resistor of the mb?
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Tuesday, February 9th, 2010 AT 4:38 AM

1 Reply

To prevent engine from overheating, the A/C compressor will shut off in 2 stages, Stage 1 (cycling), , At an engine coolant temperature of 243 F (117 C), the running time of the compressor will be reduced by 50%, cycling 20 seconds off and 20 seconds on. When the coolant temperature falls below the above specified temperature range, the compressor will resume normal operation., Stage 2 (off), , At an engine coolant temperature of 248 F (120 C), the compressor is completely switched off. When coolant temperature drops to 243 F (117 C), the compressor will run at stage 1 cycle., A/C Compressor, All the accessories are driven by one common drive belt. In case of a jammed A/C compressor, a protective cut-out switch will disengage the A/C compressor clutch to ensure continued operation of drive belt, RPM Sensors, There are 2 inductive RPM sensors for the flywheel ring gear and compressor shaft. These sensors induce alternating voltage which is used as an input signal to the control unit (overload cut-out). Depending on RPM, the alternating voltage will increase or decrease, thereby varying the input frequency to the control unit, Control Unit for A/C Compressor Cut-Out, Control unit activates compressor engagement 4 seconds after the engine is started.

NOTE: Before proceeding with test, check No. 7 fuse on 300 series. Connect Impulse Counter (013) to terminal No. 7 of diagnostic connector located in engine compartment. Turn ignition switch on. LED "U BATT" indicator on impulse counter must be displayed. If LED does not light up, test voltage between terminal No. 1 (ground) of test connector and positive battery terminal. Voltage should be between 11-14 volts. Test for voltage between terminals No. 1 and 7 of test connector, voltage should be between 6-12 volts. If not, check wiring circuit. Start impulse testing procedure. Press start button for no less than 2, but not more than 4 seconds. Observe and write down impulse readout code(s). Press start button again for no less than 2, but no more than 4 seconds. If there are no further system malfunctions, the first indicated code will reappear. If trouble codes are present, repair as indicated.

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Thursday, February 11th, 2010 AT 9:17 PM

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