GE Microwave Dead Thermostat

[Mancolt]

After lots of googling, I stumbled across some info on how to check for the source of an issue. Using a multimeter, I identified the fuse that has no continuity. However, I can't tell which fuse it is in any of the diagrams I've found online. Below are the images I took and the fuse in question. The microwave is a GE PVM1970SR1SS. If someone could help me identify which fuse this is so I can order a replacement, I will be very grateful.

I know the thermostat/fuse is disconnected in the photo. I did that to get my multimeter measure (which wasn't reading anything, just OL). This photo is oriented so that the front of the microwave (and door) are on the left side. The second is a close up of the fuse after I removed it in case that helps.

Thanks!

[ECtoFix]

The reason that thermostat read OL (open) is because it's a normally open thermostat which closes upon temperature rise.  I doubt that it's bad.  It's designed to read open at room temperature.  Here's the part:

Vent Thermostat Switch (Normally Open)

That's probably the thermostat which turns on the automatic fan.  Here's the owners manual which explains that feature.  Read page 24:

Owner's Manual - GE Profile Microwave Oven Models PVM1970 & PVM1971

[Mancolt]

Damn, thanks. I was sure I had found the source of my issue. I checked the other fuse at the top of the unit and that seemed to be fine. I replaced the two 250v 20a HVT cylindrical fuses yesterday and that didn't fix it. And the other fuse near the one I circled (in the image, it's on the bottom, located just to the left and below the one I had circled) was also okay. So I'm at a loss where to check next.

My microwave was running and then suddenly shut off. Almost as though it had been unplugged (but it hadn't). I tested the outlet, confirmed that power was getting to the fuses, but the front panel had no lights. 

What are my next steps to troubleshoot my issue if that fuse isn't the source of my problem?

[isaac]

Check the thermostat thats on the magnetron

[Mancolt]

Thanks Isaac. Can I test that fuse for continuity, or will that one show OL even if it's in working order? 

[Scottekarate]

Yes, the magnetron thermostat will be closed at room temp. It will open over 300f and close at @ 140f.

[isaac]

22 hours ago, Mancolt said:

Thanks Isaac. Can I test that fuse for continuity, or will that one show OL even if it's in working order? 

Yes,  it should check closed (OL) ,  if it checks open its bad 

[Mancolt]

On 10/27/2020 at 5:29 PM, ECtoFix said:

The reason that thermostat read OL (open) is because it's a normally open thermostat which closes upon temperature rise.  I doubt that it's bad.  It's designed to read open at room temperature. 

 

1 hour ago, isaac said:

Yes,  it should check closed (OL) ,  if it checks open its bad 

 

OL = open, right? The two quotes seem to contradict one another on that point, so just looking for confirmation.

 

As long as I get a reading close to 0 when I measure the magnetron fuse, then it's closed and fine. If I get an OL or high reading, then that fuse is the source of my issue, correct?

[ECtoFix]

41 minutes ago, isaac said:

Yes,  it should check closed (OL)

An important correction to that:

• OL means OPEN - not CLOSED.
• A CLOSED switch (or thermostat, fuse, wire...or whatever) should read CONTINUITY.  Ideally - 0Ω (Ohms) of resistance.
• OL is an abbreviation for OVERLOAD.  In other words, too much resistance for the ohmmeter to read.
• OL is a digital meter's version of INFINITY. 

Back in the day ( prior to the "90s) when there weren't digital meters, old ANALOG meters used what's called D'Arsonval meter movement to display a meter reading.  Using those MULTIMETER'S ohmmeter functions, an open circuit was indicated by its needle not moving and remained pointing at the "∞" symbol.

By definition, infinity is "a number greater than any assignable quantity or countable number (symbol ∞)".

*     *     *     *     *     *     *     *     *

This leaves me to wondering whether these basics are taught nowadays.  Being at sixty years of age, I simply don't know.

[ECtoFix]

@Mancolt,

You saw that error.  Good for you.

[Mancolt]

I got to the Magnetron thermostat and tested it. The wire connections looked to be burned up and were a pain to pull off. Lots of black fouling. When I did finally get them off, I was able to test the thermostat. At one point, after moving my probes around quite a bit, I got a reading, but it quickly went back to showing OL. And now I can't repeat. I tried to get a video showing how when I touched the flange ends of the terminals it was reading OL, but when I got near the connection points, if I had the probes in just the right spot, I could actually get a reading. I think this is still indicating that when the wires are connected to the flanges of the thermostat, they're not actually making a connection due to corrosion/fouling or the thermostat just being dead.

In any case, I think I'm going to order a replacement wiring harness since those look to be fouled up and a thermostat. If anyone has a link to the wiring harness or a part number, I would greatly appreciate it. And thanks again everyone for the help...I would have been lost without this guidance and would have ordered a replacement part that wasn't broken.

One last question: does the orientation of the plugs on the thermostat matter? IE: do I need to make sure I plug them into one side vs. the other. I'm thinking it does not, and I cannot find anything indicating a positive or negative side on the thermostat itself, so I'm not sure how I'd even tell.

Here are pictures for anyone curious.

[isaac]

I stand correct,  OL means open,  sorry: ),  any way it obviously needs to be replaced,  jowever i wouldn't buy a whole new harness,  i would cut off the burnt part on wire and put on new spades,  good luck 

[Mancolt]

Thanks Isaac. Those wires are already a bit short. I can clip them off and reinstall new spades, but it'd be simpler to just replace in my opinion. However, I'm having trouble locating this replacement part. Assuming it's $25 or less, I'd rather just get a new one and swap it out. Can anyone point me to the harness on a website? I was looking on this site since they have the thermostat in stock: https://www.searspartsdirect.com/model/531vkv9ox5-000432/ge-pvm1970sr1ss-microwave-hood-combo-parts

[isaac]

This should be the harness https://www.ebay.com/itm/GE-Microwave-JNM1951DR1BB-Wire-Harness-WB18X10492/203077515003?hash=item2f485cf6fb:g:TokAAOSwRbhfNzp

 

Good luck

[Mancolt]

Thanks Isaac. The magnetron thermostat arrived and it's definitely reading correctly on my voltmeter. I'm going to try splicing new spade connectors on so I don't have to wait for the harness.

Can you tell me what the purpose of these pieces of plastic that were around the spades before is? I cannot find them at Lowe's, so I was thinking of either shrink wrapping the connections or just wrapping them in electrical tape. Would that serve the same purpose, or just don't worry about it and pull those melted ones off before putting the new spades on?

[isaac]

2 hours ago, Mancolt said:

Thanks Isaac. The magnetron thermostat arrived and it's definitely reading correctly on my voltmeter. I'm going to try splicing new spade connectors on so I don't have to wait for the harness.

Can you tell me what the purpose of these pieces of plastic that were around the spades before is? I cannot find them at Lowe's, so I was thinking of either shrink wrapping the connections or just wrapping them in electrical tape. Would that serve the same purpose, or just don't worry about it and pull those melted ones off before putting the new spades on?

Dont worry about them,  just put on new spades,  happy to help

[Mancolt]

Just wanted to follow this up. Thanks to all the help from this forum, I was able to repair the microwave and it has been reinstalled and back in working condition. A $7.50 part (plus shipping) saved me from replacing my entire microwave. Thanks to everyone for the help!