Repair of Amana / Goodman Hotel Air Conditioning Control board
My friend is a Refrigeration mechanic fixing ice machines, freezers, and air conditioning. He calls me when he has trouble with electronic controls for this equipment.
I was asked to respond quickly to a hotel room air conditioning system which had a “fire”. A fire in a hotel is a serious problem and the manager wanted quick action. Luckily there was no fire, just some smoke in a guest room. I met him at the hotel and saw that there was some residual smoke at a through-the-wall heat pump. For those not familiar a heat pump is an air conditioner that provides cooling in summer and through reversing the refrigerant provides heating.
We removed the panel and found the board shown partially in the picture. Notice the burnt and smoke damaged components.
I removed the board and brought it to my shop. Because the burnt component was exploded and burnt beyond identification we went to his shop and picked up a spare board for comparison. Second picture shows the spare board.
The damaged component is wired directly across the 24vac input. Note the push-on connectors. This is an externally mounted transformer stepping down the mains 120vac (in US) to the 24vac which powers the control board. Close inspection revealed that the failed component is D400 on the board. This was somewhat confusing as other components D 401-404 are clearly surface mounted diodes in a bridge configuration.
Using a multimeter I measured across the good component. It measured high resistance in both directions. So it was not a diode. It looked somewhat like a ceramic capacitor. But what could be its purpose? Possibly to suppress noise coming in from the 24vac transformer. But to confuse matters further I found it was marked TVR 07470 which didn’t seem like a capacitor.
I consulted a few databases but found no matches. Finally I thought what else could be wired directly across a transformer secondary and fail in such a way?
The analysis goes like this. This control board is in an environment where voltage spikes might be present in equipment just from compressor motors, fan motors, relays, contactors, etc all of which can induce voltage spikes. At the transformer secondary was a good place to put a component to absorb these surges. I finally realized the component must be a MOV, metal oxide varistor.
On the 24vac side I knew that the allowable RMS voltage must be around 30-35vac. I looked through the catalog of a surplus parts supplier here and found some MOVs with similar ratings but nothing exact. Search on those parts I finally came up with a catalog sheet for the exact MOV and of course its specs. But no local parts supplier had such a MOV in small quantities.
Searching on eBay found a suitable replacement; a TVR 10470 which I knew from the catalog had the same 30vac spec, same clamping voltage but a slightly higher energy (joule) rating indicating greater energy absorbing qualities. At 90 cents (US) each we bought 10. My friend wanted to repair the failed board so as to have a spare. From the distributor the replacement board costs $140 so repairing one saves considerable money.
Burnt MOV was removed and the board cleaned. New MOV installed. Repaired board was tested. It performed properly.
Analysis of Failure
Voltage spikes occur constantly in motor driven equipment and heavy duty relays (contactors). The MOV eventually loses its ability to absorb spikes and heats up. It finally self destructs. In this case it was probably under specified as to energy (joule) rating.
This article was prepared for you by George Persico from USA. He is 66 years old and has more than 40 years’ experience in TV repair both Tube and Flat Screen. He also currently repairs small appliances, battery operated tools and computers.
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Ehsan Murad
January 4, 2016 at 12:19 pm
Thank you for well explained article.I just learnt what an MOV is and what it does.
Ashish
January 4, 2016 at 12:48 pm
The MOV used to fix the Amana board can be found on digikey.com. There are many brands and option for the 47v MoV. The 2 I liked most were Panasonic ERZ-V07D470 for $.28 for 10 pcs or slight higher rated joule and clamping voltage is erz-v10d470 for $0.36 for 10. Panasonic is a good brand trusted brand so a safer long lasting bet.
Robert Calk
January 4, 2016 at 12:54 pm
Nice job, George. Thanks.
Albert van Bemmelen
January 4, 2016 at 4:37 pm
Thank you very much George. This is a very well written article about those not often used but very important protective VAR components. In my repair article I had a 070271k CVR VAR1 component. Thanks to your article I now can exactly pinpoint its exact specs.
Yogesh Panchal
January 4, 2016 at 4:58 pm
Good job! Sir,
and d thanks for sharing your experiance.
Paris Azis
January 4, 2016 at 9:13 pm
Hey George
Good job! However, just in order to prevent readers from forming a wrong impression about how MOVs work and especially why they eventually fail, allow me please to correct some points of your failure analysis.
The reason you refer to that causes their failure is absolutely correct. It’s the occurring overvoltages which they have to absorb. Now the fact that over time they lose their ability to absorb them is based upon their nature… They actually react on overvoltages like a tank being filled with water. When the “tank” is full, they cannot accept more and simply explode. And this explosion is instant. There is no overheating effect before it. So we can consider them as “overvoltage counting devices” and at the same time “overvoltage absorbers”. Thus there is no underestimation of the component in your case. Even if there was a higher energy one in its place it is certain that it would explode “when its time was there”. It would simply absorb higher energy pulses, but remember here that the designer had a good reason to put exactly this one in the place you found it…
Best Regards
Albert van Bemmelen
January 10, 2016 at 7:48 am
Thanks Paris. Good to know. I have never used these components myself but in some new repair projects I examined they are being used.
Parasuraman S
January 4, 2016 at 9:58 pm
Very informative article! Good job and sharing! All the best!
Dennis Breda
January 4, 2016 at 10:48 pm
Thank you George. Well explained. You are a true professional.
beh
January 4, 2016 at 10:55 pm
GEORGE welcome aboard .good article & keep it up.
Aziz
January 5, 2016 at 5:39 am
Thank you very much.
Gary Gemmell
January 5, 2016 at 11:48 am
You need to get with modern times George and get on the internet.
5 seconds on google would have saved you loads of time.
http://www.alldatasheet.com/datasheet-pdf/pdf/119632/ETC1/TVR07470.html
Good article and description nevertheless - I have learned something new and its been a good day so far!
Thank you sir!
Gerald Millward
January 5, 2016 at 5:36 pm
Yes George, I know it's not a purist technical approach, but a quick Google of TVR 07470 would have provided a near-instant answer! If I can't conclusively identify a component from its appearance, enviroment and ID number, Google is always my first port of call.
Suranga Electronics
January 6, 2016 at 4:03 pm
Thanks Sir
SAMSUDEEN
August 26, 2017 at 4:40 pm
Very nice
SAMSUDEEN
August 26, 2017 at 4:42 pm
Very interestig