DIY appliance repair questions

[CZroe]

Today, my mother asked for my help installing a window unit air conditioner in an accessory building. Instead, I decided to take a look at the old one, since it didn’t look like the run capacitor (even electronic control panel/remote were dead). Sure enough, the fuse on the control board was blown, but it wasn’t intended to be user-replaceable.

I’ve desoldered it and the fuse is marked “T2A 250v,” which is a slow-blow 2 amp fuse. Strangely, the PCB silkscreen says “15A.” I’m inclined to go by the original fuse, especially since radial lead T2A doesn’t seem to exist from most suppliers. Is that the right call?

Next appliance is an “Americana” brand stove oven (“GE” Americana? I don’t see GE or a model number anywhere). The dial was not turning the oven off at the correct position but the “oven cycle” indicator lamp would go off at some positions where it should be on. Now it stays off but you can still hear a buzzing noise until I hit the circuit breaker to cut the power entirely. Stove part works fine.

I haven’t actually pulled the stove oven out to have a look inside yet, but I suspect that it’s going to be a bad potentiometer. My former roommate was a messy cook and I bet it got grease or something in it, though it doesn’t look too dirty under the knob (the wall and sides of the oven were filthy!).

I do have FaderLube and DeoxIT on-hand to clean and lube the pot/rheostat. Any ideas where to go next if that doesn’t work?

 

[CZroe]

For the range stove oven, I guess it really is a thermostat and not just a potentiometer because it is one piece with the temperature sensor that goes in the oven. That said, it’s obviously been arcing across the ceramic where the edge between two terminals was carbonized.

It melted the plastic backing. You might notice that the ceramic is also cracked but I’m pretty sure I did that when I was scraping the carbon with a screwdriver.

Amazon has one with packaging damage for a significant discount. Hopefully it won’t go bad too (a few reviews saying theirs only lasted a couple months).

The white thing raises and lowers when you turn the knob but never makes contact with the terminal even though it looks like it should.

 

[CZroe]

Oven works! I see a lot of reviews saying that their temperature is way off with the replacement thermostat but you’re actually supposed to adjust that by tweaking screws on the back of the knob... I just need to find a way to measure the temperature in the first place. It cooked up a nice pizza last night.

Still waiting on the AC fuse. Just went ahead and ordered the standard thru-hole T2A with radial leads.

 

[Paperdoc]

An oven temperature control (thermostat) like that works this way. The long metal tube that goes into the oven is a liquid-filled closed tube that ends (inside the thermostat) in a small chamber with a flexible disk on one side. That disk pushes against a flexible arm carrying a switch contact. As the oven temp rises the contact is moved away from its mating contact to open the switch and shut off the oven element. When the oven cools the contacts move closer and eventually connect, turning the element on. That white ceramic block you note is attached to the temperature setting knob. It is an insulator that pushes against a metal arm that carries the other contact in that switch mechanism. So by turning the temp setpoint knob, you establish the position of that second contact and hence the temperature at which it will make contact with the one moved by the liquid tube system.

To ensure that the oven temperature does do what you set with that knob there is always some way to position the stationary contact mounting system so that it makes contact at the RIGHT temperature when you set the knob. On some systems that is a lockable screw you can adjust. On mine it's a simple system on the back of the temperature knob that adjusts how the visible temp scale on the front matches up with the hub on its back to drive the shaft of the thermostat. To set it, as you anticipate, you need a thermometer to measure the real oven temperature. A meat thermometer will do IF you use it at a low oven temperature like less than 200F because that's as high as those things go. Alternatively, you can buy a cheap oven thermometer in appliance and hardware and kitchen gadget stores for people whose oven does not have a good way to control temperature. Adjusting the calibration of the oven control at ONE temperature usually is enough to get it right through its entire range.

Regarding the fuse, I expect you are right. That fuse VERY likely is NOT the fuse for the entire oven. It is, instead, the fuse for the power supply system for the control board only. The fact that is "blew" MAY mean you have a faulty component on that board that caused this failure.

 

[CZroe]

An oven temperature control (thermostat) like that works this way. The long metal tube that goes into the oven is a liquid-filled closed tube that ends (inside the thermostat) in a small chamber with a flexible disk on one side. That disk pushes against a flexible arm carrying a switch contact. As the oven temp rises the contact is moved away from its mating contact to open the switch and shut off the oven element. When the oven cools the contacts move closer and eventually connect, turning the element on. That white ceramic block you note is attached to the temperature setting knob. It is an insulator that pushes against a metal arm that carries the other contact in that switch mechanism. So by turning the temp setpoint knob, you establish the position of that second contact and hence the temperature at which it will make contact with the one moved by the liquid tube system.

To ensure that the oven temperature does do what you set with that knob there is always some way to position the stationary contact mounting system so that it makes contact at the RIGHT temperature when you set the knob. On some systems that is a lockable screw you can adjust. On mine it's a simple system on the back of the temperature knob that adjusts how the visible temp scale on the front matches up with the hub on its back to drive the shaft of the thermostat. To set it, as you anticipate, you need a thermometer to measure the real oven temperature. A meat thermometer will do IF you use it at a low oven temperature like less than 200F because that's as high as those things go. Alternatively, you can buy a cheap oven thermometer in appliance and hardware and kitchen gadget stores for people whose oven does not have a good way to control temperature. Adjusting the calibration of the oven control at ONE temperature usually is enough to get it right through its entire range.

Regarding the fuse, I expect you are right. That fuse VERY likely is NOT the fuse for the entire oven. It is, instead, the fuse for the power supply system for the control board only. The fact that is "blew" MAY mean you have a faulty component on that board that caused this failure.

Thanks. That makes a lot of sense. Anyway, I set the temperature with this:

Forgot I had it, actually, since I usually use this one:

That’s for a bench-top hot air station for electronics rework so there wasn’t any way to probe the oven with it.

Strangely, that other thermocouple came with the meter for $9 at Fry’s Electronics when they sold the exact same meter for $1 more without the thermocouple. Makes no sense! Usually a cheap meter like that doesn’t even have a continuity buzzer, but this one does.

Mine was adjustable on the knob but it was already really close (~9F). It said that each notch of adjustment was about 10F difference, but I adjusted it toward my target (400F) and it ended up overshooting to 450F (previously 391F). I ended up backing it further than where it started and now I read 405F when set to 400, which is probably within my meter’s tolerance.

The fuse is from another appliance entirely:

...an air conditioner (window unit). That’s the power board and run capacitor. Power board connects directly to the control board with a flat cable (disconnected).

We were only using the circuit breaker on the range stove oven because only the oven part was acting up but we had no other way to actually turn the oven part off while it was malfunctioning, so that wasn’t related to the fuse issue at all. Of course, your observation that it could be another failed component that caused the fuse to blow still applies to the AC just the same. We won’t know until the replacement fuses arrive next week. Wish me luck!

So far, appliance repair is pretty fun! Only moment when I felt otherwise was when I almost grabbed the thermostat while it was live because I’m so used to this thing being completely turned off at the breaker (been that way for months). The oven is a case of me finally taking things into my own hands after months of waiting for the landlord to do it. At the very least she will reimburse me for my expenses with a rent discount. The AC is a case of me trying to convince my mother to return the new air conditioner she probably didn’t need.

 

[CZroe]

Fuses for the AC arrived. Soldered one in, consulted the wiring diagram to get it all hooked back up, and... it works!

Can’t say I trust leaving it running even though this repair was actually prompted by the need to run the ”Dry” function unattended: Several months after the AC died, we noticed mold growing on the wooden furniture. The outlet or wiring had also gone bad, so we needed an electrician first, which dragged things out. Hope it wasn’t something we did when we wired it 14 years ago!

The mold is due to daily temperature swings here, where hot and humid equals nightly condensation without AC or dehumidifier. The “Dry” function is what it does 90% of the time. Being an accessory building that’s rarely occupied, AC is only desired for comfort/cooling a few days a year. A window unit AC works better than a proper dehumidifier since it doesn’t occupy floor space (building is only 16x16x16’), doesn’t need to be emptied, and provides much-needed comfort when we do occasionally occupy the building.

 

[paperfist]

Whoa someone has mad repair skillz!

 

[CZroe]

Whoa someone has mad repair skillz!

I’d love to run with that except that I took 3 times longer to reassemble because I was looking at the diagram for the compressor’s connections and not the capacitor. Add to it that I nearly electrocuted myself with the stove and I wouldn’t exactly say that I’ve found my calling. Still, I’m unreasonably proud of such simple fixes but sharing anyway in case any one else dares to take a similar plunge.

Turning trash into treasure can be very rewarding!

 

[Scarpozzi]

Appliance repairs are the way to go if you have a choice...most of the older stuff is solid state and has fewer moving parts.....OR is ALL moving parts (I'm talking about washer/dryer timer controls here...just swapping the modules when they're worn out if it's not just a contact cleaning repair).

Newer appliances are trash. Printed circuit boards out of Taiwan and Korea that aren't properly sealed to be around excessive moisture and temperature swings. I've heard more complaints from LG appliances (among others) and many of the newer designs where circuit boards replace what used to be simple, reliable relays. What would be a $5 relay, marked up to $25~30 for warehousing becomes a $15 circuit board, marked up to $150 because they can.

It's good to see you keeping the older stuff alive. That's the best practice. I'm nervous to replace our dryer after hearing so many horror stories, even on my number one brand thanks to all the energy high efficiency features they keep adding to stay competitive....it's trash. They should switch all those fancy controls for a toggle switch...even on a clothes dryer. (kidding)