Hello,
I purchased a new ac unit for a project. here is that unit Frigidaire 18,500 BTU Window-Mounted Room Air Conditioner.

Basically what i want to do is have it turn on when power is applied (plugged in). Perhaps wire the power directly to the compressor and fan but im not sure.


Any thoughts ?

 

Welcome to the forums.

That is a 240v air conditioner. You may be able to use a 240v plug in timer but I'm not sure that's a good idea. The other problem is it looks like your unit has an electronic control board which means it may not start up on an AC power up.

You really can't rewire the insides of the air conditioner to do what you want without a lot of work.

 

I linked the wrong one Frigidaire 15,100 BTU Window-Mounted Room Air Conditioner

here is the right one it is a 115v sorry about that.

 

or even if i could wire this controller Johnson Control A419 Tank Temperature Control | GW Kent to tell the unit to turn on and when to turn off.

 

What are you trying to accomplish? If you just want the a/c always on, it can be done but usually takes a lot of work.

 

i am making my own glycol chiller for beer and wine fermentation. i have 2 temp controllers i can use Johnson Control A419 Tank Temperature Control | GW Kent that one and this oneJohnson Control Digital thermostat Control | GW Kent. these monitor them temp of the glycol and tell the ac unit to turn on and then turn off.

 

I understand what you are trying to do but it is not going to be easy to connect to that logic board in the unit. You may be able to power the unit on and set the controls but when you disconnect power it may not remember your settings and not start up. Most logic boards like in that unit will not turn the unit on when power is restored.

If you were completely set on using that A/C as opposed to one with a mechanical control.... then you'd need to remove the logic board and replace it with relays or possibly interface with the relays that are in it. Your first step in modifying that unit would be to obtain the wiring diagram.

 

Maybe if i put a resister on the thermister ?? to trick it into thinking its warmer than it is ?

 

No.... you're not following my point. That unit has an electronic control board. Once you remove power from the A/C the board resets to OFF. When you reapply power..... the A/C won't turn on.

 

No i do understand that what i was trying to work around. If i change the value of the thermister then you can trick the ac unit to turn on and off at the temps you want and then i can keep the unit on all the time and not even use the Johnson temp controller. A thermister changes its resistance value as the temp changes, so if i add resisters i make the temp unit think its 70f when its really 30f so it will turn on and try to cool down. I plan to cool the glycol bath down to around 20f or so.

As it turns out these new units with electric boards now have an ability to turn back on to the previous setting in case of a power outage so you dont come home to a hot house.

 

Did you ever consider using an older a/c unit? They can be had dirt cheap at thrift stores, yard sales, etc, and have all manual controls, which are easy to bypass. All you need to do on them is pull the front cover, and you have access to all the wiring.

 

For temperature-control , a ductless "split" system would be best; an interior cooling coil and an exterior compressor and condensing coil , more simple for control purposes than a window A.C. unit.

Such a system is a "package" which includes a "wireless" thermostat.

 

I like Justin's idea of using an older unit from a thrift store because when you screw it up you haven't wasted as much money. The biggest problem is that if you want to maintain 20[SUP]o[/SUP] F in the cooler you will find that A/C units simply don't go that cold. You CAN try wiring the external temperature controller directly to the compressor (don't forget to include the starting capacitor and relay, if any) and see IF the unit can work that cold without totally icing over the evaporator coil.

You might be better off getting a small refrigerator and modifying it. The one I bought last month uses R-134 A refrigerant which is the same as is used in automobile A/C units and while not recommended a lay person CAN work on these systems.

PATTBAA, the mini-split A/Cs are LOADED with electronic controls and do NOT lend themselves to what the poster is wanting to do.

 

https://byo.com/brown-ale/item/1877-...ycol-fermenter

Here is what i am doing but instead of a 5000 btu im using a 15,100 btu unit. Like i said the new units have an auto restart function in case of a power outage so i can hook it up to a temp controller that applies power at set temp and disconnects it.

I think if i put a resister in parallel on the thermistor probe then i can use the internal temp control and save myself 70 bucks on the temp controller

 

It appears that you have already made up your mind as to what you are going to do. Good luck on your project.