great fan controller writeups off an off road site but great diagrams and ideas

[lostforawhile]

I ran across this by accident, some great circuit diagrams and ideas for fan controllers, relays for fans etc, whoever wrote this thinks like me, for example pulling the really nice hella 40 amp relays and weatherproof sockets from the yard. Street2Mud - Welcome! > CJ/yJ Electric Fan Swaps (http://street2mud.com/forum/lofiversion/index.php/t204.html)

[Dr_Snooz]

This comes at a good time for me. I've been pondering how to make my A/C more efficient. In the winter, I get nearly 32 MPG. In the summer with the A/C running, it's closer to 26 MPG. The biggest problem is that the system is set up to run flat out whenever it's on. It will dump 34F air into the cabin until the end of time. The only way to modulate this is with the heater. All well and good until your gas bill jumps.

What I want to do is make a controller to control A/C vent temps by cycling the compressor instead. I was planning to use an Arduino microcontroller, but those are complicated and expensive. Your thread makes me realize that the logic involved is simple enough that I can probably build something mechanical to do the same thing.

Good stuff. Thanks.

[lostforawhile]

This comes at a good time for me. I've been pondering how to make my A/C more efficient. In the winter, I get nearly 32 MPG. In the summer with the A/C running, it's closer to 26 MPG. The biggest problem is that the system is set up to run flat out whenever it's on. It will dump 34F air into the cabin until the end of time. The only way to modulate this is with the heater. All well and good until your gas bill jumps.

What I want to do is make a controller to control A/C vent temps by cycling the compressor instead. I was planning to use an Arduino microcontroller, but those are complicated and expensive. Your thread makes me realize that the logic involved is simple enough that I can probably build something mechanical to do the same thing.

Good stuff. Thanks.
have you studied some of the automatic AC controls used in OEM stuff? just look for the electronic avoid the completly vaccume control stuff at all costs, I dont see why something couldn't be adapted

[Dr_Snooz]

have you studied some of the automatic AC controls used in OEM stuff? just look for the electronic avoid the completly vaccume control stuff at all costs, I dont see why something couldn't be adapted

I haven't looked into it and don't know how honestly. I have a few problems at this point. First, because I'm using propane as a refrigerant, the pressures are different so I get a lot of evaporator icing. There are no controls for evaporator icing in the truck and whatever used to be in the 3g has stopped working (I think the ECU has crapped). That's my biggest problem, with the general inefficiency of the OE A/C being secondary. Much like your article, I need to monitor two temps (evaporator and cabin) and cycle the compressor accordingly. It's not terribly difficult, just time consuming to figure out how to do with no money.

Here is an interesting (ie: free) source for adjustable thermostats: AutoSpeed - DIY Adjustable Temp Switches (http://www.autospeed.com/cms/article.html?&title=DIY-Adjustable-Temp-Switches&A=112691)

[lostforawhile]

I haven't looked into it and don't know how honestly. I have a few problems at this point. First, because I'm using propane as a refrigerant, the pressures are different so I get a lot of evaporator icing. There are no controls for evaporator icing in the truck and whatever used to be in the 3g has stopped working (I think the ECU has crapped). That's my biggest problem, with the general inefficiency of the OE A/C being secondary. Much like your article, I need to monitor two temps (evaporator and cabin) and cycle the compressor accordingly. It's not terribly difficult, just time consuming to figure out how to do with no money.

Here is an interesting (ie: free) source for adjustable thermostats: AutoSpeed - DIY Adjustable Temp Switches (http://www.autospeed.com/cms/article.html?&title=DIY-Adjustable-Temp-Switches&A=112691)
there is a thermostat in the evaporator in the box along with it, the system should shut off before it ices up

[Vanilla Sky]

Arduinos are about as simple and cheap as you can get. You don't need the whole dev board when you're done, you just write the code and add the supporting circuitry, and you're good to go. If you want to start super cheap, just pick up an arduino compatible dev board from eBay and get started. For something as simple as cycling the compressor while monitoring temps, you can get away with a really inexpensive setup.

If you want it to be reliable, do seek out 105C rated parts. You need to be able to run the thing while it's hot. Atmel has several automotive grade ATMega chips that you can use. That may leave you with either having a PCB made for you (Dirt Cheap Dirty Boards (http://dirtypcbs.com/)) cheaply, then reflow soldered in a toaster oven, or hand soldered.

[Dr_Snooz]

As far as I can figure, the Arduino is $35. I tried some of the cheaper boards and wasn't impressed with the soldering. The Arduino I have has been roasting in the Fresno sun for a couple summers keeping my garden watered, so I'll stick with it. There's also a relay board for about $20 to cycle the compressor. And a couple temp sensors, ranging from $2-15 each. Admittedly not Rockefeller territory, but I can't pay the bills I have already. If I can scavenge a few relays from the wrecking yard for a couple bucks and a waffle iron controller from somewhere and achieve the same thing, then that's a big plus in my life right now.

Sounds like you know something I don't though. What do you have in mind that I'm missing?

[Vanilla Sky]

Trim down the BOM and use the lowest cost parts that meet specs. You only need the dev board to develop the circuit.

If you're not already a member of the EEVBlog.com forum, I insist that you sign up over there. The microcontroller forum is great.

[Dr_Snooz]

BOM?

I'll go check out EEVBlog.com right now. Thanks!

[gp02a0083]

Snooz a BOM is a build of materials usually required by PCB fabricators in order to take an electrical schematic and produce a spun board and silk screen(labels and icons and stuff) based on the physical specs of the parts used. I really like the arduino idea over a pure electromechanical old school way. You would not require any fancy thermo sensors, a simple cheap thermistor that's less than $1 can easily be used with an analog signal to modulate the duty cycle of the compressor. As Sky has mentioned EEVblog is a great resource. I did manage to pickup some arduino motor control and relay shields from radio shack for less than $3 a piece being they are trimming down those stores again so you may want to look around there for good deals. Looking at it really the ECU only has 2 inputs as far as the accord goes. One is for the inductor side of the compressor clutch relay (yellow wire) and the other is in series with a diode block that lead to the blue/red wire for the pressure switch and the blue wire to the fan relay. seems pretty straight forward to me if you use a lookup table with the arduino

[lostforawhile]

the AC and fan system on the lxi takes up two entire pages in the electrical troubleshooting manual. mostly to add the timer unit for the fans, and the secondary thermo switch, to run the auxiliary/condenser fan if the engine is over a certain temp at shutdown, the DX is really simple, thermosensor in the radiator, grounds the coil of the fan relay in the underhood fuse box, both fans run, the AC system is complex, but it still provides a simple ground to the same relay coil terminal, through the diode box, mine is just as simple, since I changed the factory fuse box etc, one 40 amp Bosch relay from the yard, complete with weatherpack plug, under the hood, ground from the thermo switch operates the relay coil, coil power comes from ignition, and power comes from my underhood junction block, with it's own inline fuse, actually tapped off of the wire from the alternator, since it's already going to the junction block. I've considered an additional aftermarket thermo sensor for the aux fan, so it only comes on when it's really hot, hot weather, traffic etc, I think under most conditions one fan running would be just fine

[gp02a0083]

the AC and fan system on the lxi takes up two entire pages in the electrical troubleshooting manual. mostly to add the timer unit for the fans, and the secondary thermo switch, to run the auxiliary/condenser fan if the engine is over a certain temp at shutdown, the DX is really simple, thermosensor in the radiator, grounds the coil of the fan relay in the underhood fuse box, both fans run, the AC system is complex, but it still provides a simple ground to the same relay coil terminal, through the diode box, mine is just as simple, since I changed the factory fuse box etc, one 40 amp Bosch relay from the yard, complete with weatherpack plug, under the hood, ground from the thermo switch operates the relay coil, coil power comes from ignition, and power comes from my underhood junction block, with it's own inline fuse, actually tapped off of the wire from the alternator, since it's already going to the junction block. I've considered an additional aftermarket thermo sensor for the aux fan, so it only comes on when it's really hot, hot weather, traffic etc, I think under most conditions one fan running would be just fine

shouldn't really be relying on just the electrical supplement manual. You would want to refer to page 23-7 for the cooling fan unit test. The trouble shooting guide for both FI and carb'd models for the A/C clutch and cooling fans is like 10 pages long. FYI the FI accords have a coolant temperature switch A and coolant temperature switch B that the carb'd models don't have. going completely analog controls is ok, but does not give you the control a micro controller would. lol A/C systems are complex lol

[Accordtheory]

This comes at a good time for me. I've been pondering how to make my A/C more efficient. In the winter, I get nearly 32 MPG. In the summer with the A/C running, it's closer to 26 MPG. The biggest problem is that the system is set up to run flat out whenever it's on. It will dump 34F air into the cabin until the end of time. The only way to modulate this is with the heater. All well and good until your gas bill jumps.

What I want to do is make a controller to control A/C vent temps by cycling the compressor instead. I was planning to use an Arduino microcontroller, but those are complicated and expensive. Your thread makes me realize that the logic involved is simple enough that I can probably build something mechanical to do the same thing.

Good stuff. Thanks.

I literally just wrote an entire page and gave myself a headache in the process, but I'm going to just say one thing and keep it simple. I think you can already do what you want by simply dropping the interior fan speed, since the compressor cycles on evaporator temp. (Yes, it really probably is this simple! Haha)

[lostforawhile]

shouldn't really be relying on just the electrical supplement manual. You would want to refer to page 23-7 for the cooling fan unit test. The trouble shooting guide for both FI and carb'd models for the A/C clutch and cooling fans is like 10 pages long. FYI the FI accords have a coolant temperature switch A and coolant temperature switch B that the carb'd models don't have. going completely analog controls is ok, but does not give you the control a micro controller would. lol A/C systems are complex lol
I have both the factory service manuals, and the electrical troubleshooting manual

[Dr_Snooz]

My idea was to have two thermosensors. One will monitor evaporator temp and the other will monitor cabin temp. If the evaporator temp gets below 34F, the compressor will kick off for a minute or so. If the cabin temp falls below the specified temp, again, the compressor will kick off. The thermosensor in the evaporator box already has a cutoff wire going to it, so all I'd have to do is tap into that and bypass the OE thermosensor (seeing that the OE thermosensor has stopped working, for whatever reason). The car is already wired up for me, no schematics necessary. I just have to get the stuff to make it work.

It will be a lot better than what I've been doing, which is cycling the compressor by hand using the A/C switch on the dash.

[gp02a0083]

you got a good idea there Snooz with utilizing whats there. Could you even boil it down to just one sensor for the evaporator being it is in the cabin rather than having a secondary? Either way it doesn't seem like a hard thing to do with a micro-controller and way easier and less frustrating than what you said with physically cycling it with the dash switch

[Hazwan]

My idea was to have two thermosensors. One will monitor evaporator temp and the other will monitor cabin temp. If the evaporator temp gets below 34F, the compressor will kick off for a minute or so. If the cabin temp falls below the specified temp, again, the compressor will kick off. The thermosensor in the evaporator box already has a cutoff wire going to it, so all I'd have to do is tap into that and bypass the OE thermosensor (seeing that the OE thermosensor has stopped working, for whatever reason). The car is already wired up for me, no schematics necessary. I just have to get the stuff to make it work.

It will be a lot better than what I've been doing, which is cycling the compressor by hand using the A/C switch on the dash.

I'm actually doing the same thing with my car right now since I've deleted my heater and the A/C would just run at its coldest with no way to regulate the temperature. I saw a thermostat control circuit few weeks back that I wanted to give it a try. I need to find the link again

Manually cycling the compressor is not an option as I almost crashed the other day by getting distracted with the buttons. I just took my eyes off the road for a second and then bam some idiot decided to pull in front of me

[Dr_Snooz]

The more I think about it, the less I like the Arduino for this application. The cost of an Arduino system would be over $100. And building it wouldn't be easy either. I would have to develop some kind of user interface and find a place to mount it without it looking hillbilly. By contrast, a couple waffle iron controllers and some junkyard relays would be very cheap. Some rudimentary relay logic would be easy to create and there wouldn't be the user interface to develop. There would just be a couple dial controls that I could mount anywhere discreetly. I love Arduinos, but this just doesn't seem like the place to put one.

[Accordtheory]

I am curious why none of you guys commented on my suggestion of merely dropping the fan speed. Surely you all do not leave the fan speed up, and cycle the compressor manually? An automatic climate control doesn't have to blend in hot air if it can just drop the fan speed the right amount. With a relatively low level of sophistication, cabin temp could be controlled efficiently with variable fan speed control, since the compressor cycles as a function of evaporator temp rise/load. Where I live, it is extremely humid in the summer, you would not want to allow the evaporator temp to rise above the dew point, because then it would function as a humidifier, quickly fogging up the inside of the windows.

[Vanilla Sky]

What's your BOM looking like? Remember, you don't have to use any of the fancy pre-made Ardruino stuff.

Look at it this way, you'll be able to hack in a digital climate control using a stock front end and actually have the damned thing work.

[Dr_Snooz]

I am curious why none of you guys commented on my suggestion of merely dropping the fan speed.

You must not have read the two times I mentioned that my evaporator ices up because the controls aren't working. It's a great idea, but not applicable here.


What's your BOM looking like? Remember, you don't have to use any of the fancy pre-made Ardruino stuff.

$30 Arduino Uno
$35 display w/ controls
$20 relay shield
~$25 two temp sensors


Look at it this way, you'll be able to hack in a digital climate control using a stock front end and actually have the damned thing work.

I'm thinking from a human factors standpoint. It will be more like checking my smartphone while driving. A dial is much easier and safer to adjust than a touchscreen or little buttons.

[Hazwan]

I can't really keep the fan low since it won't blow enough air to cool the whole car. And obviously turning the fan up a little made things a little bit too cold... So I had to resort to turning the compressor on and off manually to get to the sweet spot :lol:

Electronic Thermostat With Adjustable Hysteresis (http://www.zen22142.zen.co.uk/ronj/hy.html) I'm going to give this a try. Way cheaper and simpler (IMO) than the Arduino route.

[Vanilla Sky]

You don't need the whole arduino. It may be the easy button, but those are dev boards. Build up the circuit, test it, cost down the BOM, build and test again.

The ATMEGA328P-PU (http://www.atmel.com/devices/atmega328p.aspx) is the micro used in the Uno. They are $3.74 each through Digikey (http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&keywords=atmega328p-pu). Order your display from China and build your relays onto your board. Thermistors don't cost near that much money if you're not buying them from the Arduino store.

[Accordtheory]

I can't really keep the fan low since it won't blow enough air to cool the whole car. And obviously turning the fan up a little made things a little bit too cold... So I had to resort to turning the compressor on and off manually to get to the sweet spot :lol:


I was just thinking of a variable fan speed controller..that would be my best attempt at efficiency and humidity control..

[Dr_Snooz]

I'm going to PM you. I need to understand the process a little better than I do.

[gp02a0083]

Snooz, if your interested in the thermistors, I have a whole bunch here at my lab that are sitting in a drawer. I can send you a few and likewise if you are interested Sky. Shouldn't be a problem sending them snail mail

[Dr_Snooz]

PM sent.

[Legend_master]

I bought a Hayden fan controller, and wired it to the stock Fan control wires. It works like a charm. Only cost $40, and can be set to turn on at whatever temperature you want. Also works with dual fans and AC.