electric engine compartment fans

[Mike Groves]

What Gerald describes is what my '99 Marquis has.  The power comes from a post on the alternator, and the fan runs while the ignition key is on (after starting the engine) and shuts down 30 minutes after the coach is stopped. 

Mike

[Doug Allman]

ED, do you know if we can get a relay with a diode in it to protect contacts?  I want to get this back together as I am going to travel on June 20th and would like to see if it works then before we head out in August for 6 weeks travel.

Because the fans work I am making assumption the one or possibly both of the relays for this is bad. I do not know if the snap thermostat would be bad. Can you test these relays?

[Edward Buker]

Doug,

The relays are pretty reliable and I am not sure what is in there now but I will take a look. If you get a chance to read numbers and brand on yours that would help us understand if it has a diode, resistor, or nothing for suppression. It may not be what is in mine.

My guess is that the snap thermostat gives up over time. Jumper across the snap thermostat with a wire and see if the fans come on. if they do the relay is working and what you can do is buy a manual switch and install it to replace the snap thermostat for now and tie wrap it to the harness back there in a convenient place. You can then manually turn on the fans for however long you want when you come into a campground. The alternative is to replace the snap thermostat, I would possibly add the switch option also in parallel to the snap, could be handy at times.

Later Ed

[Doug Allman]

Ed, my relays are the Hella 87412. I will jumper across the snap thermostat this afternoon and let you know results.

[Edward Buker]

Doug,

My relay is a Hella 25530904 which is the same relay with a GM number. They are superseded by Hella Number H877411. This seems to cross again to a Hella 007794301 but I cannot assure these crosses. Auto parts store like NAPA should be able to verify a cross from your original relay part number if you need one. These are quite common versions so it should not be much trouble.

http://www.amazon.com/HELLA-007794301-Weatherproof-Relay-Bracket/dp/B003TEO9GU/ref=sr_1_4?ie=UTF8&qid=1464635578&sr=8-4&keywords=hella+relay

I looked at a Hella catalogue and they do not make a skirted weather resistant version with a diode. My suspicion is these are made to be outside for lights and horns and things that do not need the best coil suppression. The relay at least has a suppression resistor. One thing I noticed is that the snap thermostat on mine is physically tiny and therefor probably has tiny contacts. My plan has been to buy a physically larger snap thermostat and start there. I ordered a 130 degree max adjustable one with a 20 degree on off window and we will see if that works well. I should be able to turn the adjustment down to test it if it is warm out....we will see, may need higher then 130 degrees based on Steve's info.

You could also place a 1N4007 across the snap thermostat crimp connectors with the cathode side (lined end of the diode) toward the + lead coming from the relay and the other side toward ground. That should pass the relay coil flyback effect to ground. They are inexpensive, just insulate the leads with shrink tube where needed if you decide to do this. A bigger snap thermostat may just do it.

http://www.amazon.com/1N4007-Rectifier-Arduino-Snubber-Flyback/dp/B00LUJFFAU/ref=sr_1_1?s=industrial&ie=UTF8&qid=1464631405&sr=1-1&keywords=rectifier+diode+1n4007

Later Ed

[Dick Simonis]

Ed, how about this one with a 900 sec off delay?

[Edward Buker]

Dick,

I thought about that but it would run just 15 minutes and it ignores temperature, one in the link below. In looking for a time delay relay most are for lights or glow plugs and are not like 20 to 40 minutes. That sent me looking at little timer boards but they are not really weatherproof and would not like the engine compartment.

http://www.delcity.net/store/Time-Delay-Relay/p_804415.h_811050.t_1.r_IF3003?utm_source=bing&utm_medium=cpc&utm_term={keyword}&utm_content=Ad+group+#1&utm_campaign=Shopping+-+PLA%27s%28BSC%29&utm_keywordmatchtype={MatchType}&mkwid=8TgfXoca&crid=11472933143


A timer would run in the winter when you shut down and sometimes a warmer bed over the engine is nice. I think having the fan run longer when it is really hot, less when it is moderate, and not at all when it is chilly is what I think we are after. So I am back on a thermostat control. I plan on playing a bit and ordered an adjustable one like this. Range is 90-130F, close on rise, 20 degree difference for shut down. I think it needs contact with metal and a little thermal mass in the engine compartment to sense real heating and cooling. I was thinking of a little copper plate on a piece of the steel frame. Not sure where yet.....still thinking a bit, and like most things will require some playing around.

When we hear from Doug we will know if the thermostat is the likely culprit...

Later Ed

[Doug Allman]

Ed,  jumpered the thermostat three ways, as coach sits off, with key on accessory, with key in on position and no fans in any mode. I know fans will run with 12v power when disconnected from the wiring to the coach.

[Doug Allman]

Ed, should have mentioned that I agree with your winter, cool weather and warm weather traveling for when to let heat build in compartment and when we want to get rid of heat in compartment. Maybe the switch process is the simplest fix so you can do as you wish when you wish. Would not be terribly difficult to get a switch to a location each was happy with in their respective coach.

I would assume you would remove the thermostat and use that location to start your wiring to the new switch location.

When I jumped thermostat made me believe I must have a bad relay or relays. Correct?

[Edward Buker]

Doug,

Relay, fuse, contacts, or wiring.....I would replace the relay next after checking the fuse. I am not exactly sure if the fuse is on that board with the relays or if it is separate. In the schematic that Steve showed the ignition relay mod on, it appears to be one those the semi sealed screw tab fuse holders coming from the battery.

Yes I would start the wiring from the thermostat and probably take the switch harness up into the closet and mount the switch in a convenient spot. If you had a working thermostat and were doing this once, you could bring up 3 wires and put a switch in parallel with the thermostat that bypasses it to override the thermostat and turn the fan on when you want. One switch in series to turn the fan off if you like. If you were happy with the thermostat handling of this then just leave the series one on and the parallel one off. Simple option just one switch and no thermostat...

On the diagram it says battery power from S4 which is on the lower left of the board with the relay but no idea what S4 is from the diagram. Anyone know where the fuse for the fan circuit is? My guess is whatever is failing is likely to be common to most of us that do not have working fans. We should be able to make this system more reliable. Maybe the snap thermostats are doing the job.

One more thought, the diagram shows the fuse at 25 amps, not sure what the fans actually pull for current. We may find that the board/relay socket wiring, some connection is just not up to handling 10 to 20 amps of motor load and have to take this circuit off the board and mount some better components on the sidewall of the battery compartment....hope not.

Later Ed

[Edward Buker]

I had noticed in Mike's post that he indicated the fuse holder was mounted at the alternator. I had remembered one there, so I went out and checked it out. There is one there on mine with a label saying engine fan. I checked the fuse and it was good but was a 5 amp fuse. Hard to believe those two fans would be pulling just two to three amps as you would size the fuse to be roughly twice the load for DC motors. The schematic had a 25 amp fuse listed so the mystery continues. With the battery switches on and ignition off I had just a couple of tenths of a volt so no battery connection is being made to the fuse. Given its location it may come after the relay, really not sure at this point. Mike you have a working system, if you have a meter can you pull the fuse and check each sides of the fuse socket to ground and see if you have 12V to ground on either side....that would help. Ground probe can be on the alternator metal housing.

Later Ed

[Dick Simonis]

Ed, any chance that the fuse on the alternator is what is supplying power to the relay coil??  Kind of a convoluted way to start the fans when the engine is running??

[Jerald Cate]

Ed,

Your right about there having to be another fuse in-line somewhere.  I put an amp meter on my fans the other day and had about 26 amps startup current and about 16 amps run current. 

Bruce

[Edward Buker]

Jerald,

Another clue, thanks for letting us know. Clearly there are still some mysteries left in how these fans are powered and operate. Your current readings would indicate that the 25 amp fuse in the schematic is real, now where it hides nobody knows yet....

Dick,

That is possible, obviously the fans do not run using a 5 amp fuse alone based on Jerald's measurements. The 5 amp fuse at the alternator is a mystery, it may be physically mounted there on the alternator just as a holder given you have access to it from the rear engine hatch. Between all of our pieces of the puzzle we will get there...

Later Ed

[Edward Buker]

I had a few moments to look at the board arrangement in the battery compartment this morning that contains the relay for the fan control. Next to that relay is a fuse holder, I pulled both the relay and the fuse. The fuse was a 30 amp and it was open. I just started looking at the relay and will be checking that out. The spec on the schematic was 25 amps, maybe those blew and went to 30 amps and now that may be marginal for the fan set, not sure. Good news was all of the contacts were clean and in good shape. May still add a little corrosion X.

Message here, check that fuse next to the relay on the lower right of the board...I think without a doubt a manual switch (reasonably weatherproof if it resides in the engine bay) should be put in parallel with the snap thermostat so you can test this circuits operation anytime without having to heat the back up. It may be best to run the wires up into the closet for manual operation also if you are going to the trouble anyway.

Later Ed