Help! LCD Repair - Repairing a Homedics Digital Bathroom Scale

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Right then, the smaller wires are the 24V AC side that lead indoors and the larger wires are the higher voltage side 230V AC that remain at the H/P out side.

An easy way to determine if the wires are correct by previous means (installers or modifiers), when ever it is switched to heating mode check the rails within the furnace when operated after a few minutes to see if they are cold or hot. Caution those finned rails can get quite hot enough to actually cause burns! They should be hot when the H/P is running and thermostat in heating mode.

Also to determine the reversing valves operation by wiring, after the H/P has been off for a bit ( Edit : with the thermostat switched OFF daytime testing would be best as up to 40 minutes can be harsh during night time (it may get too cold indoors with that much time lapsing), 14 minutes is the bare minimum for guesswork testing, 40 minutes are preferred safer as there is no hourly charge theme going on, apply the thermostat temperature higher as to not start the system, then operate the range select switch from cooling to off slowly a few times and determine if the reversing valve is tied to the thermostats function by that switch control. The valve should click with the thermostat switch, On when in cooling mode, off on OFF or heating mode. May need some ears outside, or something to record the sound in remembered tandem with the thermostats switch being changed.

120V models would be rare actually, unless modifications were done, never went that route.
 
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Also the freeze up issues with a problematic reversing valve occur in cooling mode, just observe it running from time to time and look for large formations of ice on the outer rails from the compressor, a light amount would be termed normal. A stalactite formation of ice would be a bad sign drooping from the lines.

: Edited : When Summer gets back round again.
 
Those 2 cut yellow wires could be to the low pressure switch, that's an odd thing to just cut them like that, wonder what the service person knows about that... Might be aware of the valve issue and cut the pressure sensor that is supposed to shut down the unit in the event of a line problem.

Thermostat, yellow to low pressure sensor then to the contactor, the low pressure sensor gates the contactor by being a normally closed switch. When the line has a fault the switch opens breaking the circuit to the contactor shutting down the H/P.
 
Hi, GromTag. Many thanks again for your follow up.


Where are the rails within the furnace? Do you mean inside the air handler, which is located in my basement? I only have an A-coil in there and from the looks of it, a blower fan and ductwork. On the upper portion of the inside air handler are a bunch of sequencers that pass current along and start the outdoor units if I recall correctly. The only lines I see are what I think are the suction line and another thin copper line right next to that larger sweated plumbing suction line. I don't see any rails for the life of me.


I think the reversing valve is fine/operational for now seeing as how it works in both cooling mode and in heating mode. I couldn't hear that click you mentioned when hanging by the window near the outdoor unit, but I could set up an experiment with a camera recorder like you say.

I think the reason those yellow wires may have been cut by a former tech is that this unit was previously making a "screeching" defrosting noise when calling for heat a few winters ago. They moved the pins on the defrost board (TEST, 30, 60, and 90 seconds), and may have clipped those wires at that time. I was told that a certain amount of "screeching" or defrosting is normal in a heat pump, but we weren't getting heat to come on for that service call years ago. It turned out to also be a bad 1/2/3 sequencer in the air handler that time, as those can burn out a lot.
 
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Also! Some quick multimeter questions, and this should be a wrap!

I was able to measure 240V across L1 and L2 because I was instructed exactly where to put the red and black alternating current probes--L1 and L2.

I believe that the side low voltage wires on the contactor are getting the correct 24V signals, but how do I measure this 24V?

Say I want to make sure the blue side wires measure 24V. I would attach one end of the probe to the blue lead. Where would I place the other probe? On another 24V terminal, any terminal? How would I measure the C, Y, O, O, etc terminals to be sure THEY are also all 24V? One probe on C, then another probe on any 24V wire spade?

Finally, for a history lesson, I will never forget my mistake of destroying a fuse in a multimeter many years ago by measuring elements in a hot water heater, and I don't want to make the same mistake again. If I recall correctly, I was playing with continuity to see if my newly purchased water heater elements had continuity by first testing the continuity function. I touched both probe tips to each other after setting the dial to continuity mode with the three chevrons indicating sound. The probes of course made a "beep" sound when both tips made contact, signaling an electrical path/connection.

What happened next (if I recall correctly) is that I experimented with the multimeter in AC volts mode. I think (but cannot confirm) that this was where the fuse burned out. Would my touching the black and red probe tips together in AC volts mode--as I touched the tips together in ohms mode--cause the spark and fuse burnout? Should I NOT "cross the streams," i.e. black and red probe tips to each other in AC volts mode? Note that my multimeter was likely set to measure 600V AC.

Or did I measure an element wrong to cause that mistake? Perhaps I set the dial to ohms while the water heater still had electricity, and I was supposed to take out the element first out of the circuit before testing the resistance? Or any other ideas on beginner's multimeter mistakes? What caused the burnt fuse?

Thanks, guys.
 
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jburger said:
I was able to measure 240V across L1 and L2 because I was instructed exactly where to put the red and black alternating current probes--L1 and L2.
Click to expand...

This late at night, I can;t answer the 24 V questions.

There are 4 possible terminals L1, L2, N and GND. N & GND are connected together in ONE PLACE for the entire house. There is 120 VAC between N and L1 and 120 VAC between N and L2. Since N and G are connected together (you get the same between L1 and G and L2 and G). Ground would be the frame of the compressor. There should be very little voltage (ideally zero) between N and GND.

Since L1-(N-GND)-L2 is (N-GND) is connected to the center tap of your house transformer. That;s why you get 240 VAC across
s L1 and L2. So, measuring L1 to GND and L2 to ground may be safer to do initially. The outdoor unit typically does not have a neutral. Don't ask about electric dryers. 3 wire 240 V dryers don't follow the rules.


NEVER measure ohms in a powered circuit. To be safe check the AC voltage and the DC voltage, but try really hard to do so with the power off.

ALSO NEVER measure a voltage when measuring current. You generally have to use a different set of posts. Some meters fuse the low current ranges, but don;t fuse, say the 10 A range which likely uses a different input. When measuring current, most DVM's use a small value resistor. This can influence the measurement particularly at low voltages.

So, generally there is an ammeter fuse and a voltmeter fuse. They are generally expensive.

A few comments on the wiring: https://highperformancehvac.com/thermostat-wiring-colors-code/

NEVER believe colors. While W and Y and G and R were white, yellow, green and red at one time. tstats have gotten really complicated.

C is LIKELY connected to earth at the furnace and is COMMON. 24 V between Y and C means the compressor should be operating.
"O" or "B" are used for the reversing valve. See the wiring code above. I think some thermostats allow you to program the sense of the B/C terminal.

The t-stat can get pretty weird when you have dual fuel like gas and heat pump and multiple stages of heating and cooling. Then there's emergency heat.
That's where at some temperature slightly above freezing, the heat pump doesn't work well, so resistance heaters can be switched in in stages.

So, you can likely measure the voltage from Ground (the case of the AC) and Y, for instance.

Incidentally, the 24 VAC USUALLY comes from the "furnace", so the "furnace/air handler" has to be off to remove 24 VAC.
 
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Indoor rails = A-Coil, Checking to see if heating is heating.

As for the reversing valve check using the thermostat method, I was wondering if the valve switched on with the selecting switch in cool only, or might only operate when the thermostat is in run with the whole system operating.
I just get the concept that the wiring has the reversing valve active only when the system be running and irrelevant to which mode of operation via the thermostat selected, It need not be ON in both heating and cooling. The wire at the contactor looks to be orange in the pictures and connected with the yellow.

If the thermostat is in heating mode and for some reason due to wiring at the H/P were not correct, the furnace (air handler) contains 2 coils as per that plate you shown in an image from the air handler. Coils HTR1 and HTR2, those would be producing heat and the outside H/P may be producing cooling at the same time to the A-coil, not a good thing! Just to check the A-coil when the system is running to determine if there might be a fault in the reversing valve configuration.

If the thermostat is in control of the O wire and no other wire jumps or crossings exist, then the valve would be controlled by the thermostat in a means that the valve would be ok and functioning proper. Just check the A-coil when the system is heating, that's pretty much it. Again it should be rather warm to hot.

At the H/P, the wire going to the fan relay DF1 to T2 is a lower temperature rated wire, the proper wire for that terminal is currently being used for defrost boards O to somewhere else.

The 24V side? The red lead (R) and the blue/teal (C) all the others are by a function basis.
 
GromTag said:
Just check the A-coil when the system is heating, that's pretty much it. Again it should be rather warm to hot.
Click to expand...
The A-coil is warm with the heat on, so I think all is good.

One thing I forgot to mention is that we had the air handler's A-coil replaced a couple years ago due to refrigerant leak. All the R-22 (older style) refrigerant leaked out of the coil. R-22 is as expensive as hell these days ($120/lb). I hear it is being phased out due to ozone layer/refrigerant concerns. Wonder how long it'll be before they do the same for the newer refrigerant, R-410A!

GromTag said:
The 24V side? The red lead (R) and the blue/teal (C) all the others are by a function basis.
Click to expand...

So to check for 24V I should measure from the blue/teal (C) to the 1st R terminal, as in C, Y, O, O, W2, R, R, DFT?

GromTag said:
At the H/P, the wire going to the fan relay DF1 to T2 is a lower temperature rated wire, the proper wire for that terminal is currently being used for defrost boards O to somewhere else.
Click to expand...

I couldn't read the writing on that large second O terminal wire and don't feel like taking it off to swap with DF1 because of further disassembly required, and the DF1 wire might be too short to replace the O wire...

The wire at DF1 to T2, which you say is undersized, looks to say 16 AWG. With DF1 to T2 being a 120V wire/terminal connection, and per your advice, I am going out to Home Depot possibly today or tomorrow, Sun, to buy a 1-2 foot black wire. Could you tell me the correct AWG wire size and type (e.g., stranded copper) I need to buy to go from DF1 to T2? Then I just strip the ends of this larger size wire and crimp two female, metal spade connectors on the wire? Are the spade connectors also rated for specific AWG sizes?

Thanks, GromTag!
 
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@KISS - So no neutral in the outdoor unit, got it.

I printed out your great instructions about multimeter "don'ts" and have them folded up in my packaging with the multimeter. FYI, it is a Commercial Electric manual ranging digital multimeter, Model# MS8301AA:

**broken link removed**

KeepItSimpleStupid said:
So, you can likely measure the voltage from Ground (the case of the AC) and Y, for instance.
Click to expand...

Of course, we're talking the "Y" at the outside unit, right--at the Defrost Thermostat/yellow board? It's funny to me how they also call that yellow defrost board a "thermostat." As a consumer, when I hear the word "thermostat," I am thinking the Honeywell one on my wall inside my home.

Your advice to not trust the colors is duly noted. Ah, if everything HVAC/electrical could just be standardized by color code and followed to the letter--off to the gulag labor camps for those vendors/manufacturers/electricians who don't observe the color code--but where would be the fun in that?
 
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For the high voltage systems I've run 14 gauge stranded 300C wire rated to 600V, this wire gauge can take some punishment, tho 16 gauge would work as long as the temperature is at least 105-300 Celsius, 221- 572 °F stranded wire. The wire temperature is what the difference is by tolerance against loading and possible shorts within the fan motor or the pumps motor.

As for the 24V section leads, 16-18 gauge will work.

The C and the red R in the image are the 24V AC leads from the step down transformer from the air handler area.

The other defrost boards 24V leads are on a function basis only and are isolated to the 24V side during system operations, as long as the 240V side does not have a physical wire linking to the defrost board then there is no need to check voltages across the defrost board.

That wire that was placed on the O lead to the defrost board is the large rated for 240V wire, it's just being used for a 24V function and by initially seeing it with the damaged contactor, things tended to lead to a possible 240V to 24V link. That wire to the defrost board O reversing valve lead can stay in place, it's again as initially seeing it some may react and think the 240V side has been connected to the low 24V side because it's plugged into the defrost board.

The only wire that would be best to change would be the DF1 to contactor T2. 12-18 gauge, 105C, 600V.

Go with the more cost effective wire gauge if desired, 18 gauge will allow up to 8 Amps (16 Amp max typical) which is more than enough for the fan, just that the wire currently connected to the DF1 to T2 terminals is a lower temperature wire by rating.

The smaller temperature rated wire at DF1 to T2 could burn through the sheath before a safety component enacts and shuts off power. A breaker would trip at some point, higher wire temp = better chances at a safety component trip before the wire sheath gives. Most fans ampere are around 2-6 Amps, most seen, 4 Amps.

:Edited : I got scattered again.. the high voltage wire for the DF1 to T2 18 gauge 105-300°C 600V, this would be a more common wire to use.
 
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Also with the A-coil heating, the thermostat does have control over the orange wire. The yellow wire still drives the contactor in either mode of operation, seems good then.
 
Ehrmm, direct note, R-410A may not be fully compatible with the compressor out side, hence the screeching.

And the line difference to the outside unit would explain the pressure sensor being disabled as it is a weld to remove part (requires discharge of Freon and desoldering of joints to replace the part, then vacuum, leak test, then recharge R-410A with new POE oil for a R-22 to R-410A conversion) Reasons, the factory sensor may not be correct range for the new R-410A and would have continuously shut the H/P down under use and thus was not changed when the A-coil was changed, I'm assuming.

Thus, https://hvac-talk.com/vbb/showthread.php?102187-Poe-Oil
 
GromTag said:
The only wire that would be best to change would be the DF1 to contactor T2. 12-18 gauge, 105C, 600V.
Click to expand...

Hmm...

The DF1 to T2 wire says 16 AWG, 105 C on the black casing.

If it's just temperature that's the concern, and the wire potentially burning up: Given that the small black DF1 to T2 wire says 16 AWG with a 105 C temperature rating on it's casing, shouldn't I be fine after all? 16 AWG being within your 12-18 gauge specs.

P.S. I am also (maybe more) concerned with the white line 120V input wire at the contactor, L1, going to the disconnect. That wire was the burnt one (turned brown) in my pictures, and the plastic casing had separated/split open like a snake shedding its skin. I stripped it down about 1.5 inches, but there is still some "snake skin" remaining on that white wire. It is very short and shouldn't be cut further, or there will be nothing left of it. I may need an electrician to replace the large, main, flat wire (#10?) containing the high voltage black and white 120V wires that power the outdoor unit down the line... or just ask what size wire that flat wire is here and do another DIY job. Saves a $200+ service call. Just have to work up the confidence to do the job.

Off to bed now, 5am, thanks again and speak soon!
 
If the wire has the thermal rating as is, it'll have to be fine then. Just recall if another service is ever required to possibly answer the question about (if the service person even knows what is being looked at) the high voltage wire being used for what it's being used for. If the person would even ask that is

Ok then.

: Edited : 2

The above said in a humorous, gesturing manner.
 
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The unit is currently using only R-22 and has only used R-22 as far as I am aware.

So by your logic, as long as they cut the pressure sensor, is it safe to recharge the system with R-410A freon should R-22 ever cease production or is no longer available/cost effective due to price? Or would the other internals (coils, etc.) need to be changed out as well to accommodate the new R-410A?
 
Thoroughly drained, cleaned, dryer changed as it is an oil tank by design, and only if the compressor can operate R-410A. There are charts, I do not have them. The cost would be higher realistically.

I just thought with the conversation that when the A-coil was changed that Freon to R-410A change was done.

Still rather strange to cut out the low pressure switch, An Ohm meter across those two yellow wires to check for resistance only after checking them to see where they lead to first. the sensor could just be faulty, and given the task of changing one, it was cut out of operation. The L/P sensor should register resistance if still operable, tho what range a good one should be vs. that L/P sensor to determine a reason for its wires being cut.
 
Oh and some line links changed for flow difference, it's practically a new unit build with the hours on the current compressor all ready. If it turns out to be cross compatible
 

Early on in my career, I got caught up with RED being positive. In the thermocouple world, RED is always negative. At an explorer's post (Boy scouts) at Hewlett Packard, I disagreed as to what wire of the line cord should be fused. I said BLACK. You had the choice of White (N), Black (L) and Green (Gnd).

When faced with a Blue, Brown and Yellow w/green stripe in power cords, I still can't remember which is L and N. I always have to look it up or ohm it out, knowing that the wide blade is neutral from a nearby outlet to get the orientation.

==

Back to wiring. #14 is good for 15 A, #12 is good for 20A and 30 A for #10 (Fuse ratings). For a "continuous load" you can;t load the circuit more than 80%. There are temperature, # of current carrying wires in a raceway to apply.

https://www.google.com/url?sa=t&rct...pacities.pdf&usg=AOvVaw1Q4wgdQk63EgEpCcFU4T94

Finally, there is a distance correction that sometimes needs to be applied so no more than 3% of the line voltage is dropped. Basic rules anyway. I think #10 is usually used for home outdoor condenser wiring.

The AC to disconnect is usually done with Liquid Tight Flex conduit. **broken link removed**, but you don't put sheathed cables (NB-B, UF, UF-B) in them. Inside conduit wiring is usually one of these types: **broken link removed**



For giggles, here's some info on "fixture wire". https://www.ecmweb.com/code-basics/flexible-cords-cables-and-fixture-wire
 
@ KISS - See, I'm also thinking that red is always positive. DC circuits only, and not always, huh? When I changed out an outdoor sconce recently, to make sure I was getting the wires right, I was looking at some logic diagram guidelines for electricians. I remember reading about that striped green/yellow cord possibility (ground?), and which wire to attach where and such. Hard to remember for sure, unless in the business doing it every day or at least with some regularity. Fortunately, my light just had the standard white, black, and green wires. Connected color to color with wire nuts and that was that.

The wire coming out of my disconnect and going into the heat pump is a flat white cord and looks to be UF-B cable. I will jot that down and keep with the spare contactor part I have in case it needs to be changed down the line. Thanks for all the links and the wiring charts/guidelines.


Yeah, it was strange to see the wires cut. Initially, I thought they might have burned off, but now per your advice, I think it's just that pressure sensor cut out of operation. Contractors do all sorts of things to get systems running. You would be surprised what folks are willing to pay to get the heat/AC back on in an emergency (near extortion!). Homeowners just want the problem fixed and most don't likely understand the internals of the appliance, kind of like driving a car for an analogy, unless the driver also happens to be a mechanic or have mechanical engineering aptitude!

Good detective work! If I ever have the interest in taking apart the unit further, I might confirm where the wires actually go and ohm it out as you say. As for freon replacement to R-410A, great information. Sounds like a pain in the rear, and no guarantees about the compressor being compatible I see. I would probably have to go the new system route in the (hopefully distant) future, unless any subsequent Goodman repairs are simple. The unit is from 2009 according to the sticker. I hear Trane is the best quality brand in the business.

Anyway, it's day 3 or 4 now of the system running, so I guess that's a wrap. I have a 13 year old kitty cat who is nice and toasty with the heat back on, and she says "thank you meow," too. She went right over to block the floor vents to "toast" when I got the system back on. Cats and their comfort. Thanks again and great job!
 
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