Coolant fan override switch

[Leroy Eckert]

This is exactly how my system works. I would think yours is similar.
1.With the fan override off and chassis a/c off the fan will spool between
approx 400x600 RPM. This continues until the temperature reaches 195 degrees,
(190 degrees now in my coach) then an alarmstat turns the fan to high speed
approx. 1800 RPM. The alarmstat operates in an 8 to10 degree range, therefore
cycling the fan from idle to high mode over and over again, hence the cycling
you may see on the engine water temperature gauge. ( you will not see the
cycling with the chassis a/c on.) you may not see cycling in this configuration
in hot temperatures or while climbing hills.

2. Fan override off, and chassis a/c on: When the chassis a/c switch is turned
on( either pilot or co-pilot) the fan goes into high mode, stays in high mode
until the a/c switch is turned off. This takes the fan override and the
alarmstat out of the system, and provides additional continuous cooling air for
the condenser. My condenser covers the top half of the radiator. Earlier
models a/c condenser are on the roof, cooled by electric fans.

3. Fan override on, chassis a/c off. Operates the same as item 2. except the
fan override switch has now taken the Alarmstat out of the system. Using this
switch in winter in my coach holds the engine water temperature at engine
thermostat value approx. 170-175. I expect to see continuous 190 or less in
summer in this configuration.

4. When my alarmstat failed/or became intermittent I experienced creeping heat.
I'm told that alarmstat failure is suppose to default to fan high mode. I have
not verified that.

4. So you see, Bluebirds engineers forced our coaches to run on the high side of
the DD specified range ( 170-210max, alarmed at 215 degrees: Ref: 13.12 DD
Service Manual Pg. 13-48) by specifying the 195 degree alarmstat. Presumably,
the thinking is that high fan RPM robs power so the higher you run the
temperature the less fan activity. Unfortunately, that simply isn't the case
because once the 195 degree temperature is attained the fan cycles continuously
anyway. It does the same thing in my bus using a 190 degree alarmstat ,
however, the benefit of the lower water temperature is lower engine oil, tranny
and retarder temperatures.

When it gets hot, I intend to use my VMSpc to evaluate the temperature
differences resulting from my alarmstat value change from 195 degree to 190
degree. I fully expect to see a 6-8 percent reduction in drivetrain component
temperatures.

The foregoing post has been documented with temperature values, estimated
outside air temps and road conditions while driving my 1990 WB-40 over the past
5 months.

Leroy Eckert
1990 WB-40
"Smoke N Mirrors"






----- Original Message -----
From: David Brady
To: WanderlodgeForum@yahoogroups.com
Sent: Sunday, February 18, 2007 10:36 PM
Subject: [WanderlodgeForum] Coolant fan override switch


Folks,

On my '02 LXi, with the engine at idle, the fan seems to rotate
at 400 rpm or so (give or take, lol), when I enable the override
switch there doesn't seem to be any change in fan speed. Should
there be? or are there other parameters at work hear; i.e., engine
temp, etc. What are the common failure modes of the fan override?

Thanks,
David Brady
'02 LXi, Smokey
NC




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