Aircon unit refuses to turn on

[rak sa_ngop]

I have a Mitsubishi Mr Slim unit, its quite old but is rarely used so in good condition.

 

I used to switch it off at the breaker when travelling, but it was always temperamental when restarting.  Sometimes it would be a few days before it would allow itself to be turned on again.

 

I changed out the breaker but the problem remained, so since then I have always left it powered up (on standby) at the breaker when out of my condo a few days or weeks. I could always turn it on on my return.

 

Recently we had a short power failure and now I cannot get the unit to work at all.

 

Does this sound like a known problem?  Capacitor failure or some other component?

 

I plan on getting a technician out in a few days but some early insight from the TV team would be very useful.

 

Thanks

[sirocco]

Hello,

Before getting technicians, have you tried cleaning the filter.
It's very easy to clean.
I had the same problem with an old air conditioner.
after cleaning and a few kicks in the external fan, it works.

[Peterw42]

Do you mean not turning on as in no lights/beeps/fan etc on the inside unit, or the compressor not starting. Capacitor would usually be to start the compressor not power the unit on. It could be as simple as a flat battery in the remote.

 

If the unit doesn't power up at all, maybe a fuse, cct board, switch on the inside unit and could be relatively easy to repair. The indoor unit is really just a fan motor, in a non inverter unit it turns on/off the voltage to the outdoor unit.

 

[rak sa_ngop]

I have changed out the remote batteries and also tried the manual start switch inside the unit.  But no lights, no beep, no fan, no nothing.  It is completely dead both inside and outside the room.  But as I say I have had this problem before and it can suddenly start working again after a few days.  But now it has been a few weeks and the weather is hotting up.

 

It could be a fault at the breaker but I have changed it once already.

[VocalNeal]

Some AC units have a manual on/off/reset button. 

 

Open the front as you would to clean the filter and have a look around near the indicator lights It maybe behind through a small hole (tooth pick)

 

 

Edit : Oops Ok you tried this already. maybe try again after cycling the power/breaker. Is there more than one breaker/switch?

[CharlieH]

Tip: pick yourself up an electrical test pen, not expensive and it illuminates and beeps if you hold it near any live electrical source. 

An easy quick way, without taking things apart to see if a supply is getting to it, or anything.

 

Like this only 65 baht.

 

 

[dddave]

11 minutes ago, CharlieH said:

Tip: pick yourself up an electrical test pen, not expensive and it illuminates and beeps if you hold it near any live electrical source. 

An easy quick way, without taking things apart to see if a supply is getting to it, or anything.

 

Like this only 65 baht.

 

 

Every tool box should have one.  Might even save your life.

[bankruatsteve]

Just got ours fixed for a similar scenario.   A big can capacitor had failed.  B800 including service call and clean out of a bird's nest.

[alacrity]

6 hours ago, bankruatsteve said:

Just got ours fixed for a similar scenario.   A big can capacitor had failed.  B800 including service call and clean out of a bird's nest.

The internal unit runs if the ballast capacitor has failed. Not to say it hasn't failed also. Most likely there's another fault. Try fitting new batteries in the remote.

[bankruatsteve]

58 minutes ago, alacrity said:

The internal unit runs if the ballast capacitor has failed. Not to say it hasn't failed also. Most likely there's another fault. Try fitting new batteries in the remote.

In our case, NOTHING worked and it turned out to be the capacitor.  Previous problems have been an ant infested relay which only affected the compressor.  

[CharlieH]

I had this one time, ended up calling "the man", a gecko had got inside (the outside unit) and fried himself on a circuit, and shorted it. Luckily it was an easy fix, not so for the Gecko though.

[Kerryd]

If the breaker is fine and the batteries in the remote are new - call a tech as anything else would involve taking the unit apart and replacing something. Just about every large soi has a small "air con" sale/service shop (or a half dozen of them within a couple hundred meters it seems) and they aren't very expensive (usually). 

I had a similar problem with a fairly new LG air con, except that it would start manually (but wouldn't accept any commands from the remote). Called the tech, he swapped out the circuit board, everything works fine now. Cost a couple hundred baht for parts and labour.

Also, if you haven't had the unit(s) cleaned in a long time, it would be a good idea to get that done at the same time. Dirty filter screens block airflow and result in less cold air being circulated. (And they will accumulate a lot of dust even if they are in an "inside" room of the house/condo). Also get them to check the gas pressure. The last time I had my air-cons serviced I ask them to check the pressure and 2 of the units were at half the normal pressure (most air-cons will leak gas slowly and you may not even notice that it's not cooling down quite as much as it used to, as the drop is very gradual).

[cmsally]

I had the same thing happen and it was also after a power failure. It turned out there was a power surge, so something needed to be reset. It was something around the control circuit board as that is what they took apart. It was quite specific as the AC guy had to make a number of calls to the AC company to find out what had to be reset and where.

[phantomfiddler]

Do what I do, just call up an aircon guy (of which there are many) and say "My aircon doesn,t work, find the problem".

[kwak250]

I always try the Basil Faulty approach with a stick.

[rak sa_ngop]

Thanks for all the replies.  I have the ac repair man coming on Friday. Lets see how this plays out.

[andygrr]

Sticky magnetic contact in compressor outside unit give it a sharp bang to see if it opens the relay

 

[CanadaSam]

9 hours ago, kwak250 said:

I always try the Basil Faulty approach with a stick.

 

I couldn't stop laughing at the spelling of Fawlty considering the subject at hand, LOL!

[RocketDog]

On 4/3/2019 at 7:45 AM, Kerryd said:

If the breaker is fine and the batteries in the remote are new - call a tech as anything else would involve taking the unit apart and replacing something. Just about every large soi has a small "air con" sale/service shop (or a half dozen of them within a couple hundred meters it seems) and they aren't very expensive (usually). 

I had a similar problem with a fairly new LG air con, except that it would start manually (but wouldn't accept any commands from the remote). Called the tech, he swapped out the circuit board, everything works fine now. Cost a couple hundred baht for parts and labour.

Also, if you haven't had the unit(s) cleaned in a long time, it would be a good idea to get that done at the same time. Dirty filter screens block airflow and result in less cold air being circulated. (And they will accumulate a lot of dust even if they are in an "inside" room of the house/condo). Also get them to check the gas pressure. The last time I had my air-cons serviced I ask them to check the pressure and 2 of the units were at half the normal pressure (most air-cons will leak gas slowly and you may not even notice that it's not cooling down quite as much as it used to, as the drop is very gradual).

All good advice, thanks. 

 

I would add that the outside unit (condenser) radiator fins are important to keep clean. I just  cut the power and then use a pressure sprayer on a hose with a brush to clean it. This is what radiates the heat collected in your room. So it's important to keep each side of the system clean for optimum heat flow.

If the breaker is off or even pulled for safety, there is little harm even a novice can do to the outside unit with a pressure wash. 

 

If an AC guy cames out and the unit had been in service for a few years it makes sense to have him replace the compressor capacitor too, as well as a quick refrigerant pressure test, as you say. Cheap to insurance once the hood is open. 

 

Caps are cheap and take only a minute to replace. The heat destroys them and they account for a huge percentage of aircon failures. 

 

My 2 baht FWIW. 

[rak sa_ngop]

The capacitor advice has come too late.  The repair man removed the electronics unit and motor to make the repair in his workshop. He showed me a small 4cm by 4cm circuit board taken from other units in my building that had also blown.  The guy reinstalled everything today and all is working now.  He said something which sounded like 'ac' so maybe a ac/dc converter?

 

Price 2200 baht but cheaper than buying a new aircon unit.

 

Thanks for all the TV help anyway.

[VocalNeal]

On 4/9/2019 at 8:03 AM, RocketDog said:

Caps are cheap and take only a minute to replace. The heat destroys them and they account for a huge percentage of aircon failures

Capacitors are the weakest link in most electronic circuits

[RocketDog]

8 minutes ago, VocalNeal said:

Capacitors are the weakest link in most electronic circuits

Well, especially the 'wet' electrolytic type used for motor circuits because they offer high capacitance in a smaller volume for high voltage. Mainly, they are cheap to make, so that's what is used in consumer appliances. 

In serious industrial motor applications the sealed metal can oil type is used and they last for decades. 

 

For low voltage electronic devices most modern capacitors are very reliable, such as ceramic, tantalum, mica, polystyrene, multilayer ceramic, etc. At lower voltages this is easier. Ceramic caps are all but indestructible. 

 

It's all about cost though. The little blue radial-lead aluminum can electrolytic you see in cheap consumer gadgets are guaranteed to fail quickly. But then again our fickle trend-chasing acquisitive appetite results in acceptance of junk that goes in the bin (read landfill) in a year or two anyway. 

 

Professional instrument designers almost never use electrolytic caps.