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How To Repair Air Condition Digital Termostat

By on August 22, 2017
fix aircond thermostat












An air condition technician brought this for repair. It powers on but for some reason the air compressor does not kick in when it is needed.

This unit is connected to the air condition unit and cannot be powered separately.

aircond digital thermostat repair

This is an old device used for old models air condition units.

aircond digital thermostat fix

This is the model number; I found it inside the actual unit.

The problem here is how can I test a unit that cannot be powered separately? The simple answer to that is I have to test all the parts on the board one by one. That is not the best way to do repairs.

how to repair aircond digital thermostsat

Since the problem was the compressor line, the common sense suggests starting on that line and see what is going on there. The next step is to find that line.

how to fix aircond digital thermostat

I checked inside the unit; the compressor is line three.

aircond thermostsat circuit board

In order to trace pin three, I had to take the relay off board. The relay was the main connecter to that line and the best way to start is checking the relay.

aircond relay

Arrows show the coil pins. I applied 24 volts there and it clicked when I checked for continuity on the other pins, there was none. Ah, a bad relay.

24 volt aircond relay

Here you can see the specification of this relay. A common relay in air condition units and was not hard to find. Once I replaced the relay, I took it back to the customer’s house, hocked it up and powered it up, it worked like a charm.


Sorry, could not take a picture of that thing working. It is not any easy thing to do at a customer’s house.

repair aircond thermostat

It was a common sense repair, although I could not power it up. Always ask customer about the fault and do your own search and repair.

Mission accomplished.

This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.

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  1. Yogesh Panchal

    August 22, 2017 at 10:26 pm

    Well done! waleed.

  2. Parasuraman S

    August 22, 2017 at 11:39 pm

    Yes, I agree, the first input or clue we get to service is from the user. Good job!

  3. Hicham CHAMSI

    August 23, 2017 at 2:44 am

    Dear Waleed Excelent approch for solving the problem.
    keep the good share.

    i have 1 question? i am working on Cebora tig 180. with yellow led on, i found a faulty open resistor with 268OHMS reading instead (red violet black) so it should be 27ohms, when i replace it by new 27ohms 0.5w it get burned again; in the board there is no short; regulator voltage is ok, the ics are not hot. so please have you some suggestions how to attack the problem quickly? thanks in advance

    • Waleed Rishmawi

      August 23, 2017 at 1:41 pm

      Hicham: did you check the GBT transistors or the diodes in the output section? I had that problem before and the transistors and diodes were shorted. do an ohm test between the red and black terminals on the outside of the machine? what reading are you getting there. you are still having a short in the machine.

  4. Hicham CHAMSI

    August 23, 2017 at 2:45 am

    i forget to tell you i have no schematic.

    ok waiting for your reply.


  5. Albert

    August 23, 2017 at 10:38 am

    To keep my post short and simple like your good article. Good repair and deduction Waleed!
    If they only would be able to produce transparant relays it would make fault finding looking for burnt contacts a bit easier. But since they are mostly only housed in black plastics they probably are safer and easier to manufacture.

    • Waleed Rishmawi

      August 23, 2017 at 1:36 pm

      Albert. they still do have relays that are see through but it is still the same process. even the contact are seen and they are black you can not open it and fix it. the easier way is to take it off board and use a dc supply and check it out. thanks for the nice comment.

  6. moshe jacobson

    August 23, 2017 at 6:30 pm

    very nice...a good repair!


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