Cess,

Here you go. I hope the format comes out correctly. If not, let me know, and I'll email you the correctly formated PDF version. This Thermostat switch should be a single stage. I also recommend you to use an adjustable temperature range thermostat switch. If you have to buy a fixed temperature thermostat switch , you must match the temperature setting to the thermostatyou have installed on the engine. I have added the full legend to tell you how everything works.

Wow, it's been a while since I read and wrote simple HVAC electrical schematics.

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HAHA...simple. All I see is Greek!!!

thanks Ken!! I'll definitly be giving this to the electrical guy at work to go over with me **ahem**decipher.

 

Ken, shouldn't the high come on with the AC?

 

Yes, normally it should, but as this is a two speed, you can use the low speed providing the MarkVIII can pull at least over 2000 cfm's. That is why I stated earlier about most vehicles only uses a single speed fan, then the wiring would be much easier. I am sure that 2000 cfm's is enough to cool the A/C as the OEM electric fan only pulls around 2000 cfms.

 

If it were me I'd either wire it for low with a/c off and high with a/c on or wire it constant on with the ignition switch in high speed only. I don't think the low speed on the fan pulls enough cfm to keep the engine cool anyway unless it's winter in Chicago and you're coasting down hill in neutral. Low speed might be good in the midwest, up north, or on the east coast, but where I'm at it only gets into the 50's and 60's for maybe 2 1/2 months tops, so I view the low speed as useless.

Cess, I hope the fan works out for you, because I know you can feel the hp difference without the clutch fan stealing power from the engine, and I'm still waiting to see how this all plays out with you and MG before I try it

 

Not to be a pest Kensai or to challenge your knowledge, but I've done a lot of "e-fan homework" especially in the required cfm department as I want to do this to my D too. In my seach for information I checked Perma-Cool's website (an e-fan manufacturer) and this is what they reccomend for cfm requirements for general applications.

"In choosing an electric fan for primary cooling, four cylinder engines generally require 1,600 cubic feet per minute (CFM) minimum. Six cylinder engines generally require 2,000 CFM minimum, small cubic inch eight cylinder engines require 3,000 CFM and large cubic inch eight cylinder engines require a minimum of 4,500 CFM. Recommendations are based on stock engines and regular driving conditions. CFM estimates are based on the electric fan mounted behind the radiator in a "pulling" configuration. Electric fans mounted in front of the radiator, in a "pushing" configuration, are only 80% as effective." quote from perma-cool.com.

Hope this helps everyone keep their Ds cool and kick'n. It's helped me re-think my approach to this job.

 

You have to remember, the wiring I setup is made for two speed fan motor. To optimize the use of both speeds, I put the A/C on the low side and the temperature switch for the high side.The low speed speed setting should be enough to pull air across the A/C condenser, but may not be enough to cool the engine with the added heat load from the condenser. This is where the temperature switch will automatically kick in and flip the fan to high speed mode to keep the engine cool and at the same time still keep the A/C cool. All this and no manual intervention from the driver. Last thing a driver needs is more distraction when they should be concentrating what is up ahead on the roads!

I would assume the CFM rating of the low speed setting of the fan should at least be half of what the high speed is. If the MarkVIII high speed is rated up to 4400 CFM, then the low speed setting guessing should be at least 2200 CFM. 2000 CFM is more than enough air flow to cool the A/C condenser coil when the D is sitting still and idling.

Remember, 2000 CFM that I am referencing is only for the low speed setting to provide enough cooling for the A/C. 2000 CFM is not enough to keep a 360 engine cool. That is where the high speed settting to give up to 4400 CFM will take over automatically when the engine temperature reaches the set temperature set point and bypass the low speed setting. Once the engine cools down to a set point on the thermostat, the high speed will dis-engage and low speed will resume if A/C is still running. If A/C is not running, the fan will not be running at all. This is an advantage for cold starts. When you cold start your D and the A/C is not running, the fan will not engage and let your D warm up quicker. This is a big plus for those owners that live in very cold climates.

Here are some scenarios of how my wiring works:

Engine hot (engine thermostat set point IE: 180 or 195) - High speed
A/C running and engine running cold/warm - Low speed
A/C running and engine running hot (engine thermostat set point IE: 180 or 195)- high speed
Engine running cold and no A/C (IE: cold start or cold winter season) - Fan is OFF

Wiring diagram shows that under no circumstances that power is simultaneously supplied to both speedsto the fan. The relays are wired so that it supplies power to either high or low or no power to fan.

Again, the wiring diagram I created is design to 100 percent automate the use of the fan on both high and low speeds without any manual user intervention just as if it was a OEM setup.

 

Ya Ken I think he should run it high speed only if it's enough to do the job, or run low speed on a temp control to kick on at 180 and cut out at 150 andrun the high speed to kick on at say 190-200 and cut out at 180 at which point the low speed would cycle on and pull down to 150 and cycle off.

This could be achieved using two adjustable temp controls tied into an additional relay to insure voltage supply to only one speed at a time by wiring the speed selecting relay NC to low speed and NO to high speed and the coil to the hot on the high speed after the temp control relayso the speed selectionrelay will automatically cut power to the low speed when the high speed is being called for and will switch back at 180 and then completely of at 150. In theory this should work good for cold winters as well as hot summers and if you wire it to a constantly hot power supply it will continue to cool the vehicle after you shut it off, however I would reccomend battery rundown protection if wired to a constant hot source.

 

You got it. But I am trying to keep things as simple to wire up for Cess. Throwing in another thermostat or subbing to a two stage thermostat may be more than Cess can absorb!

Hence why I prefer to fork out the extra extra money and buy a two speed fan controller that can simplify all this and make everything really easy to wire up. The only bad thing to the fan controller, this is a single point of failure and not cheap to replace. The home made setup, if one of the relays goes out, you can replace it cheap or swap it with a good relay to temporary get by until you get a replacement. (In diagram, you only worry about the thermostat relay as this is the high speed relay), if this goes out, you can swap out with the A/C relay to get by temporarily.

 

Well since this has gotten hot I thought I'd let you guys know that my D has been running good with the e-fan, I still have to fab up a shroud for it and I will be set. The ac still brings the temp slightly above the 200 mark and I don't like that but it doesn't go past that and my ac is still nice and chilly. Once I get into school (diesel tech training) I will be able to work on the D in a shop and won't be frying my ***** off at 100 degrees in the shade. I will be getting a lot of work done hopefully if they give us enough shop time. Good luck in all of your endeavors guys and if you go with a switch you may want to stick a post it on your steering wheel for the first few weeks to remind you to turn on the fan. It is like second nature for me no and I am done with messing with that end of it.