Hi Guys,

I recently made a shed in my home as a small make shift office space. I bought a portable air conditioner to cool it.

After using it for a few months its control card stopped working and that pushed me to open it and look inside. I have never worked with an air conditioner before so I googled allot to learn how an AC works and figured out that the control board was just a bunch of microcontrollers reading in from thermostats and switching the compressor on and off.

So I removed all control circuits, wired the AC fans to the power supply, and also hotwired the compressor and its capacitor to the mains power coming into the unit. The thing works fine, blows cold air in, and hot air out.

But to save on electricity bills I wanted to have the compressor switched on and off so I added a heavy duty electrical switch between the mains and the compressor. I use this switch to turn the compressor on when things get hot, and I switch it off when it becomes nice inside, all this while the AC fans keep running normally.

Here's a picture of the installed unit


So basically "I am become PCB". I control the compressor.

My question is, would this hurt the compressor? Like I usually turn it on for 5 minutes and keep it off for 10-15 minutes. Does this switching on/off frequency damage the compressor in any way??

I have done a little googling on how the ac control PCB decides when to turn the compressor on and off. And what I have found is that there are two temperatures that it considers for turning the compressor on and off.

1. Ambient air temperature: Compressor turns on when ambient air temp is above the set temp, and off when the target is achieved.
2. Evaporator (cooling) coil temperature: Compressor turns off if the temperature drops below +3 degres celcius to prevent frosting.

So to me it seems like if I abuse the compressor and keep it on, it might hurt stuff, but as long as I'm careful and not turning it on for long periods of time it should be fine. I just wanted to get a better opinion on this so I have joined this forum.


Thanks allot.
This is a lovely community.

 

What you are doing is fine. Instead, I would buy a thermostat so that it cycles the air conditioner automatically.

 

One thing to be careful of is not to turn it back on without leaving it off for a few minutes.
The compressor can lock up and not start otherwise due to residual pressure built-up in the condenser side of the unit.
This can burn out the motor if it's not otherwise protected (which it may be).
Ideally you would want an added time delay to insure that it can't be restarted for a few minutes after it has stopped.

 

There are 3 situations that would be a good idea to avoid ........

1) Short-Cycling,
The Compressor should be given ~3 to ~4 minutes for the Pressures to equalize before a "Re-Start".
Generally a Thermostat will handle this on it's own,
just because the Temps in the Room probably can't change that fast,
BUT, in the case of a very short Power-Outage, the Compressor may be asked to Re-Start against it's
full operating pressure differential, which it may not be able to deal with.
This could result in the Compressor-Motor being "Locked-Up" and start cycling on
the Thermal-Protection-Device that is built-into the Windings of the Motor.
This can cause extreme over-heating of the Motor, and if this happens enough times, may destroy it.

A "Delay-On" Timer set for ~3-Minutes will completely solve this problem.

2) Freezing,
Freezing-up of the Coils is an unusual situation, and usually won't cause any damage.
It usually occurs due to a clogged Air-Filter, and may require several hours to thaw-out on "Fan-Only"
and only then be capable of returning to normal-operation.
This is usually avoided by using the Thermostat for dual-duty.
The thermostat will have a Copper-Sensing-Tube that is routed very close to the Evaporator-Fins,
but not actually touching them.
If Ice starts to build-up on the Evaporator,
Ice will come into contact with the Thermostat-Sensing-Tube and cycle the Compressor Off.

3) Excessive-Condenser-Pressure/Temperature.
If the Fan somehow stops, or the Condenser has inadvertently blocked air-flow,
the Compressor will become overloaded and will overheat.
This situation is normally monitored by a "High-Pressure-Switch" which will Cycle-Off the Compressor.
This protection is sometimes provided by a "High-Temperature-Switch",
which can work equally well to protect the Compressor.

I would try to use the Thermostat(s) or Pressure-Switches that came with the AC-Unit as
they are positioned and calibrated to work well under all possible adverse conditions.
.
.
.

 

Given that an air conditioner must be able to operate constantly cooling in some anticipated conditions, switching it off occasionally will not be a problem. As others have stated, an immediate attempt at a restart can cause problems. What was not mentioned is that most refrigeration compressors, at least for units in the USA, also include an added overload/overheat thermostat to switch off the applied power if the compressor does not start, but instead heats up. That function usually protects the compressor from damage.
So my simple safety advice is to ALWAYS switch off the ac unit completely when you leave your office. AND, as has been already said, always wait a minute or two to switch back on after switching off.

 

Thank you so much guys. I have learned a ton. I will be adding some automated control on some weekend.