1998 Air Conditioner, Duo-Therm PENGUIN, convert to digital control

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G

Geze

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Joined
Jul 12, 2020
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5
Hello,
Does anyone have any insight as to how best to convert an analog controlled roof mounted Dometic Duo-Therm Penguin 600 series Air Conditioner to a digital control?
One of the reasons I would like to do this is to get the fan to turn off when the compressor is not running. With the current set up running the AC you have a choice of Low, Medium or High, fan constantly running regardless of whether the compressor is running or not.
Thanks
 

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It won't be easy.  Your A/C uses a line voltage thermostat that directly switches the compressor motor's power on and off.  A/Cs using a wall thermostat have a relay interface to let the low voltage thermostat control the A/C functions.

You may be able to find the interface box at an RV junkyard but considering the A/C is 22 years old the most practical solution may be to replace it with one that already has the interface built in.
 
After reading the modification that was done to the Casita camper I am not sure this applies to my situation as I do not have a wall mounted thermostat. All the controls are mechanical dials on the unit itself, no wiring coming off of the unit.
 
As mentioned by Lou, the task to add a digital control, and my interpretation is a wall mounted digital thermostat, is pretty challenging. You would have to access the internal wiring of your AC and make modifications to bypass the dial thermostat and the fan/cool control rotary switch, run control wiring from the AC to the wall thermostat as well as run DC power wires for the wall thermostat and also add a relay board to the AC so that the digital wall thermostat could interface with the AC to control the compressor and fan.
Newer ACs have a control box that contains a relay board that allows an analog or digital thermostat to control the AC.
1. Determine how you would run the wiring from the AC to the digital thermostat. I don't think your AC has duct work in the ceiling.
2. Do you have a way to run DC (battery voltage) to the digital thermostat and also to the AC.
3. Once you solve 1 and 2, you can investigate adding an AC control box to your existing AC, such as where can it be mounted in the roof enclosure and how to modify the AC unit's wiring to interface to the control box.
 
Working around factory machinery I've seen a 120v relay used to start a secondary (or slave) device like a fan. Wouldn't it be possible to jump the compressor 120v to a relay to turn the fan on and off with the compressor? That would eliminate the need for an additional thermostat.
 
This is the schematic to the air conditioner if it's any help.
 

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The schematic makes it easier.  Move the thermostat so it feeds the selector switch instead of just the compressor.  Note this will make the A/C inoperative (including fan and heat, if present) unless the thermostat is turned up enough to call for cooling.

If you're in a humid environment shutting down the fan at the same time as the compressor may let the evaporator coil ice up, in which case all you can do is wait until the ice melts.  Turning on the fan by itself may speed the process.
 

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Thanks for your help in this Lou. I'm not sure I follow this modification but I'll have a friend who's smarter than me take a look. Maybe there would be a way to put a delay of a specific time for the blower to turn off as well.
 
Sorry to keep this topic going but wouldn't a 120v coil relay like this cut power to the blower fan when power to the compressor turns off? The wiring looks super simple to me. I am also tired of getting up at 2 AM to turn the A/C off to keep from freezing.

https://www.hvacquick.com/howtos/howto_relay.php
 
It would, but it's not necessary because the fan draws very little current compared to the compressor so the relay isn't needed.  Here's a step-by-step after giving it a little thought.

1) Remove the two wires from the thermostat and jumper them together to take the thermostat out of the compressor circuit.

2) Locate the incoming hot (black) AC line.  Disconnect where it joins the a/c wiring.

3) Take that incoming AC to the Line terminal of the thermostat (it may or may not have this marking).

4) Connect the LOAD terminal of the thermostat to the remaining side of the connection you took apart in Step 2 so it turns power on and off to the selector switch (fan and compressor).

 
I would not suggest shutting off the fans.. I worked in an office with a "Computer room" A/C (Very loud) and it is amazing how after a while your brain filters it.. In my Motor home I have ducted A/Cs and oen of 'em I have to physically focus on it to hear if it's running.. the other one is a bit louder (but also in a quieter part of the RV) still I hear the compressor kick in and out (Change in sound) but don't really hear it run all that much.  HIGH COOL or OFF only two settings I use.
 
Lou Schneider said:
It would, but it's not necessary because the fan draws very little current compared to the compressor so the relay isn't needed.  Here's a step-by-step after giving it a little thought.

1) Remove the two wires from the thermostat and jumper them together to take the thermostat out of the compressor circuit.

2) Locate the incoming hot (black) AC line.  Disconnect where it joins the a/c wiring.

3) Take that incoming AC to the Line terminal of the thermostat (it may or may not have this marking).

4) Connect the LOAD terminal of the thermostat to the remaining side of the connection you took apart in Step 2 so it turns power on and off to the selector switch (fan and compressor).
Click to expand...
Ok, thanks very much! I will take a look at that.
 
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