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Topic: 40 hp Hydraulic Cooling Fan Motor - Manual Speed Control (Read 1068 times) previous topic - next topic
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40 hp Hydraulic Cooling Fan Motor - Manual Speed Control

Yahoo Message Number: 68940
Hi Coach Owners,

This post illustrates a method to manually control the subject fan to primarily get lower transmission temperatures in stop and go city conditions.
Fan control is either by the Sauer -Danfoss controller or by the engine ECM. The SD controller has inputs from coolant temperature and air intake temperature sensors. In addition, dash a/c is normally an input.

The transmission is cooled by piping inside the engine radiator.
The intercooler has its own radiator in front of the engine radiator with the hydraulic radiator below and unitized with the intercooler radiator.
The dash a/c has its own condenser mounted in front of the intercooler radiator.
There are four fan speeds on SD controller coaches: 0-500, 800-1300, 1300-1800 and 2600 rpm.
The speeds are covered in the Fan.pdf test procedures found in the Files section.
This post provides an approach to cooling the engine, transmission, and dash air conditioning for SD fan controlled coaches for the following conditions: slow city traffic which raises transmission temperature, dash air improved cooling, long climbs and under high outside temperature conditions.

It consists of the following added controls.
1.   Electric fans installed in front of the dash air condenser.
2.   Control of the coolant temperature sensor. A 100 ohm resistor is placed in parallel with this sensor using a relay to obtain the fastest radiator fan rpm. This is a safer approach than switching the 12vdc power to the SD controller as some coach owners have done.
3.   Control of the dash air relay. The dash air relay is energized to obtain the two middle radiator fan rpms with the higher of the two based on engine rpms.
Note: item 2, resistor value was obtained from the coolant temperature sensor temp vs, resistance curve and 3, hookup was obtained from the Fan.pdf test procedures and foldout S0699.
The Control approach is simple and consists of 3 dash mounted switches, 2 relays, 2 fuses, 2 diodes and one resistor along with appropriate wiring.
Photos are attached in the Photos section entitled 40 hp hydraulic motor fan speed control.
They show the 3 switches mounted vertically to the right of the accelerator pedal, the diodes placed inline with wire #300 to the dash a/c relay, the relay added to parallel the 100 ohm resistor with the coolant temperature sensor and the relay added to turn on the 2 added fans.
Static test results were different than expected. Namely that cooling fan rpm increased somewhat proportionally to engine rpm with either the 100 ohm resistor paralleled or the dash a/c relay energized. Below shows the 40 hp fan speed for several conditions.
Engine temp at 130 deg F

Engine rpm Switches off 100 ohm resistor paralleled Dash a/c relay energized

700      140 rpm    1154 rpm      1164 rpm 1000      151      1617         1612
2200      637      2828         1734

Note: At engine 700 rpm (idle), the fan rpm increased very slowly as the engine warmed up.
Next, roads tests will be performed to analyze dash a/c cooling differences with the added fans in front of the condenser and with the engine at various road conditions to monitor transmission temperature differences using manual fan rpm control.
A report will be posted.

Fred Kovol

2000 Allure 30593