Air Con PCB repair : some general question

[dicky96]

Hi guys
I've been getting more air con controller boards of various brands for repair - mainly the ones from the outdoor compressor unit and I realise I have a lot of gaps in my specific knowledge, while being pretty good at electronic repair in general.

Does anyone know of any good resources for information on this sort of repair? I'm hoping here there will be some guys who are experienced in this. I'd specifically like more info on how the controller PCB works, because I expect they are all pretty much the same, and especially how it communicates with the indoor unit (protocols, method etc). I can generally fix these boards if they have an obvious problem such as burnt components, low value power resistors gone high, shorts, low voltage (standby) PSU not working etc etc. The ones I am struggling to understand is where the board will power up on my bench, On these boards I have 12V, 5V, 24V whatever and often have some flashing LEDs and hear relays clicking so the microcontroller is doing something at least but the customer is reporting some error code like EL10 or F4. I need to understand how this works, where the errors are coming from (microcontroller on the outdoor unit board?) so I have some chance of diagnosing the fault. Another thing I have read about is the eprom on the controller board often causing this type of error. I've tried to find out if this eprom holds firmware or if it just holds preset user data but that info seems hard to come by. In other words is this a common failure ,can they just be replaced, or do I need firmware and if so where to find it. There are a lot of aircons here and talking to companies who fit them, nobody on the island is repairing the boards. So that sounds like good business to me. Another thing I am interested in is putting some sort of test rig together on my bench to help me. For example I already use an old passive PFC choke as a makeshift reactor coil to power the boards up.

So I have a lot of questions in my head as this is a new area of repair work for me, can anyone help enlighten me or at least point me in the right direction?

Thanks
Rich

[sam_sam_sam]

If you are talking about condenser coil defrost boards if so one major failure is the terminal area on the bottom of the board corrosion on the traces bad temperature sensors bad relays for cooling fan operation bad thermostat wiring from the condenser unit to the thermostat on the wall

Two things to check when the customer complains about the condenser coil freezing up ( in the winter ) first thing to check the temperature sensor fan control relay and a reversing valve relay on some models

One note some defrost control boards can affect the cooling function especially if it has a temperature sensor for outside temperature and not the temperature sensor on the condenser coil it just will not activate the anti cycling timer and act like the thermostat is bad not necessarily

If you have the new air conditioner controller boards that have error messages you need to get the troubleshooting manuals and keep them where you can easily find them and if need be call the manufacturer for the air conditioning unit if you do not understand the error message that is given

On occasion I have had to do this because the information given in the manual does not really make sense sometimes do not be afraid to call tech support for a better understanding of the error code message

One note on variable speed evaporator cooling fans and variable speed compressors are sometimes a nightmare to figure out what is going with them

One thing about variable speed compressors some controller boards have a troubleshooting function that can sometimes help you find the cause of the problem that are going on you need to find the troubleshooting manual for how to use this feature some of these troubleshooting functions are not all like and some of them are worthless because they are trouble makers that they are not worth anything for troubleshooting any kind of issue

One other note sometimes defrost board are to badly damaged from a very bad voltage spike or by lightning and not worth trying to repair them one word of caution be careful of some manufacturers recall notices because sometimes this what is causing the issue at hand you have research the problem you are faced with if you have not seen this issue before

Here is a case in point I once went to a customer home to look at his dishwasher because it was doing weird things that it was not supposed to do things like you would select a certain type of cleaning cycle and was supposed to have a certain amount of time well this was not what it was showing unfortunately and the other weird thing was the timer was not counting down continuously either some times it would get stuck doing the rise cycle and not go to the next step so I did some research on where to buy another controller board well I found that but that was not the only thing I found I found several forums that talked about the issue with this particular controller board how even replacing the controller board a week or a month later you could have the same issue again with the controller when I told the customer about what I found out they decided to buy a brand new dishwasher and the one they had was a little over two years old no extended warranty was purchased at the time of purchase

I once went to a customer house and he tells me that what is weird was the evaporator cooling fan would not always turn on when the thermostat was calling for cooling oh really I like to see this and sure enough when the thermostat was satisfied and went to cycle back on again the cooling fan was barely running and then just stopped turning altogether hun I look at the back of the fan motor and it was a variable speed fan the one that has the VFD module mounted on the back end of the motor these things are expensive to repair if you can still get the modules but when I got the price of the module versus the complete motor and VFD module there was only about $75.00 different in price the customer opted to buy all of it brand new over $500.00

One note about checking the functionality of a defrost controller board off the condenser unit I not sure if this can be done reliably or not because when I repair them I reinstall in the unit to test them to make sure that they are functioning correctly or not

In a past life I used to do air conditioning work for a living and you would not believe some of things I have learned and run into