Mechanics

BLOWER MOTOR NOT TURNING ON

1982 Mercedes Benz 300td

Heater problem
1982 Mercedes Benz 300td 6 cyl Two Wheel Drive Automatic 168000 miles

So I checked the power at the " plug" that plugs into the blower motor and I am getting power there. I ordered a used blower motor for an auto recycling place and I put it in. Still the same problem. They say they tested it before they shipped it, but of course anything can happen during shipping. Could it be anything else that is preventing the motor from turning on? A resistor or relay? What about the heater control valve? What does that do? I need to get this problem resolved before winter hits and im shivering my way to work! Thank you.
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Weldinggoddess
September 10, 2010.



Climate control problems in a Mercedes you might as well commit suicide. Here are a few diagnostic tip to help you get started, if you have any questions, report to the engineering, that is deck 27 just in case you forgot.

TESTING
SYSTEM GENERAL TEST
Following test sequence shows proper system functions in all operating conditions. It should be used to attempt to pin-point possible problem area in system. Start engine.

Selector at " 2" OFF Push Button; Blower at " AUTOM" Heater valve is closed. Compressor is off. Main air door is closed. Blower is off.

Selector at " 72" Economy or Heat Push Button; Blower at " AUTOM" Slowly rotate dial near " 72" until " overlap" occurs (floor outlets and center outlets are both open). Heater valve cycles every 4-5 seconds above 77 °F (25 °C) coolant temperature. Compressor is on (Heat), after a.7 second delay. Main air door is open. Blower starts after approximately 10 second delay. Auxiliary water pump is on.

Selector at Minimum Cool; Maximum Push Button; Blower at " AUTOM" Heater valve is closed (energized). Auxiliary water pump is off. Compressor is on if ambient temperature is above 40 °F (5 °C). Main air door is at recirculation position (80% recirculated air). Blower at next to highest stage.

Selector at Minimum Cool; Economy Push Button; Blower at " AUTOM" Heater valve is closed. Auxiliary water pump is off. Compressor is off. Main air door is open. Blower is running at next to highest stage.

Selector at Minimum Cool; Heat Push Button; Blower at Low Speed Outside air door open. Heater valve is closed. Auxiliary water pump is off. Main air door in recirculation position. Blower running at low speed.

Selector at " 72" Heat Push Button; Blower at " AUTOM" Move dial until both floor door and center outlets are open. Wait for blower to reach next to lowest state. Heater valve cycles 4-5 seconds. Compressor is on. Main air door is open. Auxiliary water pump is on.

Selector at " 72" Economy Push Button; Blower at " AUTOM" Blower moves up one stage. Heater valve cycles every 4-5 seconds. Compressor is off. Main air door is open. Auxiliary water pump is on.

Selector at " 72" " Economy" Push Button; Blower at High Speed Blower at top speed. Heater valve cycles every 4-5 seconds. Compressor is off. Main air door is open. Auxiliary water pump is on.

Selector at Maximum Heat; Heat Push Button; Blower at " AUTOM" Heater valve on. Auxiliary pump on. Compressor on. Blower on at next to highest stage. Center air outlet closed.

Selector at Minimum Cool; Maximum Push Button; Blower at High Speed Air should come immediately out of center outlet. Outside air door is open.

Selector at " 72" Off Push Button; Blower at " AUTOM" Heater valve closed. Auxiliary water pump off. Main air door closed. Blower and compressor are off.

Selector at Maximum Heat; Heat Push Button; Blower at " AUTOM" Detach lead from cold engine lock-out switch. Main air door is closed. Blower is off.

Selector at Minimum Cool; Heat Push Button; Blower at " AUTOM" Main air door is at recirculation position. Blower comes on after 10 second delay. Reconnect the cold engine lock-out switch. Chuck A.

ETR SWITCH TEST
1. With system operating at maximum cooling for several minutes, place thermometer in center outlet. Depress Low Blower speed button and Heat push button. Temperature dial should be at minimum cooling.
2. Run engine at 2000 RPM. After third cut-out of compressor clutch, outlet temperature should be approximately 40 °F (5 °C), but not below 37 °F (3 °C).
3. If temperatures are not as stated, check A/C system for proper R-12 charge and output. If okay, check position of ETR capillary tube. If okay, replace ETR switch.

VACUUM TESTS
Before beginning tests, run engine until it is fully warm (cold engine lock-out switch is off), then shut off engine. Depress Economy push button.

Check Valve Detach Red/Green vacuum line or Green/Gray (except 300SD, 380SEC and 380SEL) vacuum line from check valve (in line from manifold vacuum source). Attach vacuum tester to check valve port and apply vacuum. If vacuum leaks down, replace check valve.

Vacuum Reservoir Detach Red/Gray vacuum line from check valve leading to vacuum reservoir. Connect vacuum tester to vacuum line and apply vacuum. If vacuum reading changes, replace vacuum reservoir gasket or vacuum reservoir.

Switchover Valves
1. On all models, detach Red/Green vacuum line or Green/Gray (except 300SD, 380SEC and 380SEL) vacuum lines from check valve and attach vacuum tester to vacuum line. Apply vacuum. If vacuum changes, test switchover valves individually. Remove lower right instrument panel trim piece.
2. Remove right side of center console to expose switchover valves. Individually pull vacuum lines from each switchover valve, attach vacuum tester and apply vacuum. If vacuum drops, switchover valve is leaking and should be replaced.
3. To double check, energize switchover valve by turning ignition on and depressing Off push button if testing defrost switchover valve or fresh/recirculation switchover valve (short stroke). If testing other switchover valves, depress Maximum push button instead. Vacuum should drop if okay. Turn off ignition and replace trim pieces.
4. Apply vacuum while watching operation of defrost door. If vacuum drops, replace vacuum actuator or vacuum line. Check mechanical operation of door also. Reattach vacuum line.
5. Detach Red/Light-Blue vacuum line from check valve in line to center air outlet. Attach vacuum tester to line and apply vacuum. If vacuum drops, replace line or defrost vacuum actuator.

Center Outlet Vacuum Circuit
1. Remove glove box, lower right instrument panel trim piece and right side console trim piece.
Detach Red/Light-Blue vacuum line from check valve in line to center outlet vacuum actuator. Plug end of vacuum line.
2. Detach vacuum connection from center outlet switchover valve. Attach vacuum tester to this line. Apply vacuum. If vacuum drops, replace center outlet vacuum actuator, check valve or vacuum lines in this circuit.

Heater Outlet Vacuum Circuit
Pull Red/Yellow vacuum line from floor outlet switchover valve. Attach vacuum tester to line. Apply vacuum, noting operation of floor air doors. If vacuum drops, replace floor outlet vacuum actuator or vacuum line.

Outside Air Door Vacuum Circuit Detach Green vacuum line from outside air door switchover valve. Attach vacuum tester to line. Apply vacuum. If vacuum drops, replace outside air door vacuum actuator or vacuum line.

Fresh/Recirculated & Main Air Door Vacuum Circuit
1. Detach Red vacuum line from " long stroke " fresh/recirculation switchover valve. Attach vacuum tester and apply vacuum. If vacuum drops, replace vacuum line and check or replace " long stroke" or " short stroke" fresh/recirculation vacuum actuator. 2. Detach Green/Blue vacuum line from " short stroke" fresh/recirculation switchover valve. Attach vacuum tester and apply vacuum. If vacuum drops, replace vacuum line and check or replace " long stroke" or " short stroke" fresh/recirculation vacuum actuator.

IN-CAR OR HEATER TEMPERATURE SENSOR TEST Remove appropriate sensor as described. Using ohmmeter, check resistance value at electrical terminals of sensor. Compare reading with values shown in following chart.
IN-CAR & HEATER TEMPERATURE SENSOR RESISTANCE
Ambient Temperature °F ( °C)Ohms
59 (15) 15.7
77 (24) 10.0
95 (35) 6.5

REMOVAL & INSTALLATION CONTROL PANEL ASSEMBLY
Removal
1. Disconnect battery. Remove radio. Remove optional switch, if equipped. Remove 2 screws in radio opening and carefully pull out and remove wooden cover panel out from bottom.
2. Remove 2 screws retaining control assembly and pull assembly forward. Remove instrument lamps. Detach 12-pin connector from control unit. Temperature dial and blower switch can be removed independently at this time.
3. To remove push buttons or blower switch from control panel, remove screw near blower switch. Remove plastic cover from control panel assembly. Remove push buttons or blower switch as necessary.

Installation
To install, reverse removal procedure.

ELECTRONIC CONTROL UNIT AND/OR BLOWER SPEED CONTROL UNIT
Removal Disconnect battery. Remove glove box and lower right instrument panel cover. Detach electrical plug. Remove retaining screws and remove control unit.

Installation To install, reverse removal procedure.

Dr Loot
Oct 5, 2010.


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