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Old May 28 2021, 12:13 AM   #5845
Zelandeth
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Join Date: Mar 2013
Location: Milton Keynes

Fan of: Dragonsdawn
Now Reading: Working my way through the whole Pern series
Default Re: What is happening

My bodged air conditioner control setup worked perfectly overnight and through most of the afternoon when I was back in the room. Right up to where the compressor made an unpleasant noise then stopped. Fear not, I'd just not done a good enough job of soldering one of the wires to the PCB so it had cracked the joint and come adrift. You remember me talking about how I wasn't a fan of it and the testing setup needing to be beefed up long term? Yep, there's why! Vibration has a tendency of finding any weak spots for you in settings like this in a hurry.

A bit of hot glue is now providing mechanical support in addition to me having remade the two solder joints. I actually took the PCB out to do that this time rather than soldering it while working left handed half buried in the back of an air conditioner like last time. Correct operation was restored.

After a thorough search only requiring me to upend around 80% of the north wing loft I tracked down the little temperature controller I remembered still having leftover from another project a few years ago.



Between the size of it and the fact that I was absolutely positive that the box was almost entirely blue it's quite surprising that I found it at all - assuming that there isn't another one up there of course!

Just a cheap generic little unit I've seen badged under about a dozen different brands, but it does what it says on the tin. These are all of about £15 on eBay/Amazon so even if they don't last forever it's not the end of the world really. Honestly I'd struggle to build one for less...and that's assuming I already have a suitable enclosure and LED display in stock.



Very simple to wire up, four sets of two terminals on the back: Mains in, temperature probe, then two pairs of relay contacts for the heating and cooling loads.



The internal relays are rated for up to 10A at mains voltage, though precisely how far you want to trust the relays in a control this cheap is up to you. For this application I'll be using the existing relays in the air conditioner to do the heavy lifting, this will just be the brains of the operation.

Couple of advantages in using this control over the original setup on this unit/or my bodge currently in operation.

The first is that it will be able to seamlessly handle both the heating and cooling side of things from one control. The original control system allowed the unit to run either as an air conditioner or a heater (it's just a 1.5kW resistive heater rather than a heat pump sadly), but required the user to manually switch modes. In this application I'm not likely to ever really call on the heating side but this feels like a more elegant solution.

Secondly is being able to dial in an exact temperature. The existing thermostat has an arbitrary 0-9 numeric scale, just being able to dial in whatever temperature I want is definitely my preference. Especially as the coolest setting on the existing stat is only just cool enough for me to be comfortable overnight.

Being a dedicated temperature controller it also has properly configurable hysteresis and anti-cycle timer settings - both things that I really wish the fancy pants wireless thermostat for the household central heating system had!

The existing PCB will basically just be relegated to being a source of the 24V relay control voltage and fan speed control once I'm finished.

Just need to figure out a tidy way to fit this. It's a shame the existing thermostat cutout isn't a tiny bit bigger or it could just slot in behind the front panel there.



May still be able to get away with it - not particularly worried about losing a bit of the left side of the display, but big question will be whether I can fit it back there and still properly access the buttons.

Might be a nice little evening project for next week if I have time. At least the AC is working properly again now though so some of the heat (pun entirely intended) has been taken off the job.
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