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I am attempting to build a raspberry pi controller for my MasterCool swamp cooler, which has a rather dumb controller. The cooler has the 24V low-voltage control kit (as opposed to 120V or 240V direct control) installed.

Today I was messing with the control wires after popping the thermostat off, and mistakenly jumpered some of the connections, blowing the fuse. I've ordered new fuses, but in the mean time, I'm not sure how to properly control the blower (high and low) as well as the water pad pump and drain pump. I have terminals in the cooler labeled FAN, PUMP, 24V, COM, and DRAIN. I've confirmed that I have about 24VAC between the 24V connection and COM. The other connections all seem to have 0 potential difference with ground.

Given that I want to avoid blowing more fuses and doing this wrong, how am I supposed to power the various components? Should I be jumpering them to the 24V line? Do I need resistors to limit current?

Thanks for reading, hope I've not messed up in some way, this is my first SE post.

Brock Tice
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  • I would guess that the 24V domain is the control system. 24V is probably used to run it because it's a decent voltage for driving the elements (like power transistors, triacs or relays) that control the motors, yet is a low enough voltage to be safe for control panels. I.e. the 24V supply probably does not drive the various motors directly. But you also cannot drive 24V lines directly with the Pi. It would help (the project, and the above question) to obtain or reverse engineer a schematic of the system. As it stands, there is not a lot of information in the question. – Kaz Aug 26 '13 at 22:41
  • Is it really 24VAC, or is it DC? – Kaz Aug 26 '13 at 22:44
  • It's 24VAC for sure. My multimeter reads ~0 in DC mode, my understanding is that the whole system voltage is stepped down using a transformer. – Brock Tice Aug 26 '13 at 22:46
  • As for driving the 24V lines, I've already ordered a relay board that will let me handle the power. – Brock Tice Aug 26 '13 at 22:47
  • I'm trying to reverse-engineer the system. I can't find any schematics. The company that makes this system, Adobe Air, went out of business ages ago, and was bought by another company, which also went out of business. Most people apparently have simple rotary 120V switches that control their systems. We inherited this setup with the house when we bought it. – Brock Tice Aug 26 '13 at 22:51
  • You are right! Flipped the meter to DC today while it was running, checked the terminals at the other end (in the cooler), and lo and behold, it's 5VDC to drive the pumps, 5VDC for high speed on the fan, and 2.5VDC to drive the low speed on the fan! – Brock Tice Aug 29 '13 at 20:58

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Brock,

I'm trying to set up the same for my MasterCool. It currently has the MasterStat CC1000 or CC2000 (not sure which model), for which you can find a manual at http://paseoalegre.com/index.php/download_file/34/. My "MasterStat" control panel in the house has 4 wires which according to the manual work like this:

  • G: ground (have to identify the color, maybe grey?)
  • R: 24 VAC (not sure what this is for, but potentially to power the control panel?)
  • W: water pump control; 4-5 VDC to turn it on, 0 VDC otherwise
  • Y: blower speed control; 0 VDC for off, 2-3 VCD for low speed, 4-5 VDC for high speed

Then there is an appliance control board next to the MasterCool on the roof that translates these control panel inputs into the proper outputs to drive the motor and the pump.

Curious to hear if you learned more.

Christoph
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I've never needed to cool a swamp ( :-) ), so this is just an educated guess.

Based on the information provided, it appears that the FAN, PUMP, and DRAIN leads need to be connected to 24V to activate that function. If you have the original contoller, it should be possible to verify this by measuring between the appropriate terminals on the controller with an ohmmeter, with the controller set to activate the various functions.

Peter Bennett
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