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Old 03-14-14, 09:33 PM   #1
jeff5may
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Default Zero dollar repair of Haier window a/c

I scored a Haier HWR12XC5 window air conditioner on craigslist last weekend for $20. Owner said he had it for 4 months, then came the thunderstorm. He said lightning hit a pole near him and took out all kinds of stuff in his house. The insurance company cut him a fat check, and let him keep all his dead equipment.

$20 later and a quick trip to my house, here's the unit:



It seems previous owner had done some minor disassembly of the unit, as the bracketry and screws were lost. We don't care, screws are cheap and less work for me. Luckily, this unit is an RCA/GE original "works in the drawer" unit. A frame inside a frame, if you will. The guts just slide out after you take out like 3 screws (something they did with lots of appliances back in the day). I yanked the works outta the drawer, plugged her in, and found the unit was stuck on high fan. The unit wouldn't power up or anything. So I took out 1 screw and out came the control board.



Quickie check revealed main fuse OK, transformer OK but running hot, and hardly nothing after main rectifier bridge. So I unplugged it and started taking resistance measurements.

This unit is so simple, I didn't need a schematic to figure out what was wrong. I just looked up a few datasheets to verify main components. The brain is an 8-bit microcotroller, an 86C807Ng, flash programmed at the factory. It has 1 temp sensor, a thermocouple. An Ir sensor feeds right into the micro, for the remote control that was also lost. Muscle control is done by a ULN2003A, a package of digital switches. When the micro sends out 5 Volts to the switch, it turns on a relay. The other side of the switch can take up to 50 VDC at 1/2 Amp per switch. Easy peasy.

The power supply has 2 parts: raw DC and 5 Volt regulated DC via a 3 pin regulator. I checked the input and output for ohms and got 3 ohms on the input. The 5 Volt line had like 50K ohms.

Guess what the raw DC runs? a bunch of sugar cube relays and the 5V regulator. That's it. Since the unit was forever stuck on high fan, I removed that relay first. Lo and behold, lots of ohms on the raw DC rail now. I set he control board in a safe spot, so it wouldn't short out against anything, and plugged her back in. Voila, lights!

When these units are first plugged in, they light up like a car dashboard and beep. That was somewhat of a surprise. Then they go dead again for like 10 seconds while the micro initializes. After that, you can push buttons and do something. I set the unit to low cool and turned the setpoint down and it fired right up. I let it do its thing on low and took more readings.

The high fan relay control line had not changed a bit after setting the unit to low cool: zero volts and like 3 ohms. A few minutes after startup, the fan motor shut off unexpectedly while the compressor remained running. I unplugged the unit and didn't even need to touch the fan motor: I could feel the heat on my face when I looked close. It had shut off on high-temp limit.

Now tell me what's wrong, batman.

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Last edited by jeff5may; 08-14-17 at 08:38 AM.. Reason: reposting pics cuz of photobucket
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Old 03-14-14, 09:54 PM   #2
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Make sure it's not trying to activate both high and low on the fan.
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Old 03-14-14, 11:39 PM   #3
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Was it really a zero dollar fix? As in no parts used to fix it? Was something bridged/shorted?
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Old 03-15-14, 12:17 AM   #4
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I would be suspect of the Transformer as it would of been the first in line to take a jolt or surge from that lighting strike.
if its not that remember the surge did not make it to the fuse so look for damaged before it.

Sometimes you can literately smell the problem part..
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Old 03-15-14, 03:50 AM   #5
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Hint: my suspicion is that the root cause was not lightning damage at all...

To be continued after work
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Old 03-15-14, 11:05 AM   #6
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Were the bearings in the motor seized or excessively tight?
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Old 03-15-14, 08:08 PM   #7
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Those 7805 voltage regulators sometimes go bad if the input voltage is too high - common practice when they are simply stealing DC from a 12V or 24V circuit.

My guess though is that you have a bad run capacitor.
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Old 03-15-14, 09:41 PM   #8
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Hey now! Mike wins.

It looks to me that the previous owner ran this baby nonstop and didn't clean the filter. Once the filter clogged sufficiently, the trap was set. The motor quickly heated up and heat cycled for a long time, and toasted its sleeve bushings. Not enough to seize up, but enough to cycle on its heat overload and draw way too much current.

This lack of maintenance dominoed all the way to the digital switch chip. The motor tried to draw excessive current through the itsy-bitsy sugar cube relay. When it died, it shorted all its parts to each other. Its contacts tied together, causing the fan to run constantly. The coil shorted, killing the high speed fan switch. Luckily, the rest of the IC survived, and the mayhem didn't make it to the micro.

When I pulled the high speed fan relay, the short through the IC output remained. However, the remaining switches in the IC still worked. Like usual, the manufacturer didn't fully utilize the IC, so it had extra unused switches in it. So, I rigged the high speed relay to another switch. For wire, I harvested an old phone cord.


input on left:green wire jumped to micro. output on right: red wire jumped to relay, trace to original output cut.

To find a replacement for the dead sugar cube relay, I went into the shed and found something dead. These things are in everything with digital controls nowadays: cable boxes, space heaters, fans, dehumidifiers, crt monitors, etc. I recycle my electronic waste, it's better than radio shack nowadays. 90% of the rest of the world doesn't throw away items of value because they need repairs, so why should I? If I can't use or cannibalize them, I trade junk with someone who can.


Can you tell which cube I replaced?

So after some micro-tiny soldering with a magnifier and my regular sized iron, I moved on to the root cause. The filter got a shower while I found my sewing machine oil. I love that stuff because it's thin and penetrates like WD-40, but remains. Plus it's in a bottle with a retractable straw that will fit WAAAY down in between tight things (like a window a/c fan motor) without dripping oil all over everything or dismantling the world to get to it. I applied a generous amount (ten drops or so) to each side of the motor, spinning the shaft a few times along the way, until it felt very free.

I let it sit for a while so the oil could penetrate, while I did a visual inspection on the rest of the unit. One thing I noticed immediately is that although the heat exchangers have more surface area than older, vintage units, the tubing is smaller and spaced closer together. As a result, they are thinner and lighter. They also have more elaborate circuitry than the old ones did.


evaporator - 4 circuits


condenser - 2 circuits that merge at bottom

After finding the vent lever in the blower cavity and snapping it back onto its post, I plugged it in and turned it on. Now it works perfectly. I'll take some measurements tomorrow.

Last edited by jeff5may; 03-17-14 at 05:00 PM..
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Old 03-17-14, 01:17 AM   #9
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Was it the larger cube without the sticker that you replaced ?

I like your Style , fix it don't turf it

I think its Commendable - Good Job !
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Old 03-17-14, 03:57 AM   #10
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Ecomodded,

To be clear, it was the second from the left in the pic. The furthest left is the compressor contactor (with the red and white wires attached to the top). From left to right, the remaining sugar cubes control high, medium, low fan. These two types of relays are what the mfrs have been using in all manner of appliances for decades. For example, in a microwave oven, the control board would have one of each type in it. The contactor would control the magnetron tube, the sugar cube would control the exhaust/cooling fan. If you had a range hood microwave, it would have all four of the relays in this air conditioner (and maybe more, to control lights and such).

The scrappers in town love me. They pick up dead stuff and do a quick troubleshoot if the thing isn't real heavy. Sometimes, we can bring the dead things back to life in the driveway in no time. If it's netr (not economical to repair), it's trade, gut, or off to the scrap yard time. Like any machine, some parts are very valuable if they still work. The yard pays by the pound, ebay does not.

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