electric engine compartment fans

[Dick Simonis]

Ed. just looking at mine briefly, it appears the thermostat is directly in line with the fans and carrying full amperage.  Two wires from the fan and the thermostat is series with the white wire which than goes to ?.  No idea what the temp rating is but if I get time when we're done packing I may pull it out and look or at least try a jumper.

One thing that bothers me is that these button T-stats tend to be surface reading and it's screwed tight to piece of wood.  That being the case it would read the temp of the wood not the air.

Still a bit of mystery.

[Michael Rump]

Ed,
Opens at 150F and closes at 135F.

Found the following Redi-temp thermostats that are close;
3455RC-100-229 Open at 155°F Close at 125°F
3455RC-100-230 Open at 165°F Close at 135°F

Regards,

[Edward Buker]

Dick,

If that is the case no wonder it fails, really bad design. That may make the relay an ignition relay that will only be on when the ignition is off maybe, just cooling once you shut down? Anyone have the original design working, is it interlocked to the ignition? We could add a relay if the fan load is fed through the thermostat.

Michael,

I think the high end would be the close and the low end the open? This seems like quite high values to me, does it work well with that range? I just put an order in for one of these adjustable versions up to 130F anticipating that mine has failed.

http://www.amazon.com/Emerson-3F05-1-Adjustable-Snap-Control/dp/B000PY7T7I?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

Later Ed

[Dick Simonis]

I totally agree the design appears lacking but the other question is what is the power source.  It must come off some protected circuit whether is ign on/off or either.  I need to stick my head in the battery and electrical bays and see if there is a clue.

[Edward Buker]

Dick,

Doug Allman sent me a cryptic schematic and there is a relay on the board in the battery compartment that seems to control this that I attempted to describe in my prior post. It is the relay on the lower right of the board in the battery compartment. If labeled it would be CFR.

Later Ed

[Jerald Cate]

I located this device in the engine compartment on the DS wall above the engine fan assembly.  I haven't had any luck locating a data sheet or supplier source, maybe some of you other guys are better parts chasers.

Bruce Cate

[Steve Huber Co-Admin]

Bruce,
I wasn't able to locate the part #. Give Ken a call at BCS as he may know the correct temp range for the fan control snap disk thermostat.
Steve

[Michael Rump]

Print attached.
Regards,

[Steve Huber Co-Admin]

Thanks Mike. I missed your post of the temps.

Bruce, here is a replacement for the fan control thermostat based on the temps on the schematic. http://www.supplyhouse.com/White-Rodgers-3F01-150-3-4-Snap-Disc-Fan-Control-Cut-In-150-Degrees-F-Cut-Out-130-Degrees-F-14695000-p

The circuit as designed will cause the fans are run any time the engine compartment is 150F or higher, ignition on or not. It's not clear to me how effective they are when the engine is running and one is driving down the road. Addition of another  relay between the thermostat and GND will enable the fans to start and run when the ignition is off and the temp is above 150 to exhaust the built up heat in the engine compartment.  See attachment. Just a thought..

Steve

[Gerald Farris]

These fans were wired in the original Beaver built coaches, pre 1994, so that they turned on with the ignition switch and when the ignition was turned off, a timer was activated that powered the fans for an additional 30 minutes after ignition shutdown.

The bed was directly above the engine in all of these coaches with very little insulation below the mattress, and since heat soak in the mattress was such a problem, no thermostat was ever used, just the timer.

Gerald 
 

[Edward Buker]

Mike,

Now that is a schematic I can live with, old school :-)

So there is no magic here, it is about as expected. The coil of the relay is energized by the thermostat turning on. The relay contacts close and handle the motor load through the fuse from the battery as a supply, so there is no ignition interlock. The only thing missing is a suppression diode across the relay coil. Without that you will get arcing and erosion pitting of the thermostat contacts, as they open, when the relay coil field collapses. That is a likely source of our fails. Should be able to get a relay that fits with that diode protection built in. If the hand notation on the schematic I got from Doug is correct the relay is a Hella 87411 which at least has a suppression resister across the coil which is a help, a diode would be better.


Later Ed

[Edward Buker]

Steve,

Added circuit looks like a good idea if the fans indeed run while cruising down the road. My sense is you would not get to 150 degrees while moving at any reasonable speed. Since mine has never worked i really do not know. Anyone have a sense how often this kicks on and has a working version?

Later Ed

[Steve Huber Co-Admin]

Ed,
You are probably right, depending on location of the thermostat, although some of the newer engines are running pretty hot so overall compartment heat also increases.  In any case, I think it would advantageous to have fans start exhausting immediately on shutdown rather than waiting for temp to reach 150. Gerald's comment re a timer is also an approach but it seems to  me temperature would be more effective. Only downside with temperature trigger is that you would probably increase battery drain.
Steve

[Doug Allman]

I did find the thermostat in my coach. It is on the upper wall of the engine compartment behind the coolant tank and very close to being right above the turbo. about 15" above the turbo.

Those numbers on the drawing are from my Hella relays. Would we be able to change to a different relay so that we would not continue to loose the relay ?

Also only get cooling after the coach has stopped. If we go to that use I would believe we would want to cool down to somewhere near or below 100 degrees. We would not necessarily need a high and low just a relay that would keep fans running until below the set temp. The mattress even with some insulation in the later model coach's still gets very warm, in the summer travel.

Looks like I am glad I brought this up. Could help a lot of us. Thanks to all input so far.

[Edward Buker]

Doug,

It is a good post, this fan thing has been a a bit of a mystery to most of us as to where things are and how it is supposed to work. You do need a "window" of on off temp with a sensor or it would just keep cycling. Looks like about 20 degrees on most of these thermostats.

Steve,

I do like the info that Gerald passed along and the old way may have been better. Best of both worlds...Seems like a 110 F cut off thermostat in series with a 30 minute cycle timer that is initiated when the ignition is in the off state would be a good way to go. Runs 30 minutes only if over 110F and only for 30 minutes but a settable timer module might be better given you could set it as you wanted. Could be wired in and live right in the rear closet area given the thermostat is below it.

Later Ed