Frigidaire Gallery FGMV175QFA Microwave Trips Breaker When Turned On

[swataz]

Hi all,

Yesterday, after completing a cycle and taking food out of this microwave, it suddenly shut off. 

After checking, it had tripped the circuit breaker line it was in which is a dedicated line for this appliance. This had never happened before.

I removed the panels, broke out the ole multimeter and went to work. The fuse was fine. All the usual suspects had continuity when they should have and none when they shouldn't.

Once the breaker is reset, and the unit is tried again, the same thing happens. I other words, it isn't dead, something is just causing a short but I can't tell what.

At this point I am clueless. I read somewhere that a high voltage capacitor could be the culprit but also read that usually the case when the microwave isn't working at ALL.

Again, it is a Frigidaire Gallery FGMV175QFA over the range microwave oven.

Any advice is welcome. 

Thanks!

[ECtoFix]

Very likely a door switching sticking.  There should be three of them - primary, secondary and monitor. 

By design, the fuse should blow if a switch sticks.  However, with it being a 20a fuse and the circuit breaker possibly being either a 15a or 20a one, the breaker might be tripping before the fuse blows.

Anyway, although the fuse didn't blow, normal repair practices calls for replacing the door switch if the fuse blows.  Beings that your problem occurs upon opening the door further confirms that the door switch is likely the culprit.  A good visual inspection and testing with a meter can be done to verify.

I would recommend replacing all three switches.

[swataz]

Hi and thank you, ECtoFix. What you are saying makes sense, but I do have a question about the continuity results.

Would I necessarily get "good" results from all of these switches if one or more were sticking?

Just trying to get my head around this.

Thanks again.

[ECtoFix]

In the case of microwave ovens, those switches will STICK due to pitted contacts.  Here's why:

Pitting occurs over time and is caused by the arcing which occurs each time switch contacts make or break during their closing or opening to energize/de-energize a circuit.  It's a normal occurrence in ANY mechanical switching device.

In your microwave, the door switches carry ALL current flow demands to energize the high voltage transformer (along with everything else).  The HV transformer's power requirements are significant.  How much that is varies with your oven's wattage rating.  To give some idea of that power, it's about the same as if you had SIXTEEN 60 watt light bulbs running from the same electrical outlet.

So, as switch contacts become pitted, they'll have less CLEAN usable contact area.  Additionally, what carbon build that there is (due to arcing) m-i-g-h-t conduct current flow, but with some resistance.  In either case:

• Current flow through electrical resistance causes heat
• Insufficient CLEAN contact surface area (of the switch contacts) relative to current flow demands will ALSO cause heat

The "sticking" begins to occur when the switch contacts get hot enough to weld together.  However, the switch's internal spring tension can overcome that if the welded areas are minute.  A given failing switch may remain stuck CLOSED j-u-s-t long enough to disrupt the sequence designed between the operation of the three switches in there.  If the three switches (primary. secondary, monitor) don't open or close in proper sequence, a direct short occurs.  Those three switches (as an assembly) are called the "door interlock" and are a MAJOR safety aspect of the microwave.  They prevent ANY possibility of the oven still "microwaving" when the door is opened.  By design, if the interlock's sequencing has failed at ANY point and no matter HOW briefly, the fuse is there to blow and shut everything down.

.........................................................

NOW...I don't know what kind of meter you're using and what your definition of CONTINUITY is. 

Some meters have that BEEP feature to indicate continuity.  I personally DON'T use that feature since, depending on the meter, some meters will BEEP when resistance is as much as 20 ohms or less.  W-E-L-L...20 ohms is NOT continuity.  For that matter, 2 ohms isn't either.  So, you could be thinking there continuity when there is actually more resistance than the switch should have.  However, the ohmmeter may STILL not adequately reveal that there's a problem since an ohmmeter can't LOAD the switch with current flow like actual circuit operation does.

There's more I could write, but that's enough of this lesson.  I hope I gave enough so that it helps you understand it some.

[swataz]

That's an education! Thanks!

I ordered all three of the switches and will report back when I get them which should be end of this week, likely Saturday.

Again, thanks for that awesome, thorough description of the issue.

[Jonathan Ayala]

On 5/11/2020 at 7:01 PM, swataz said:

That's an education! Thanks!

I ordered all three of the switches and will report back when I get them which should be end of this week, likely Saturday.

Again, thanks for that awesome, thorough description of the issue.

Did replacing the switches fix your problem?

[swataz]

There are two parts to this answer.

I was only able to replace one of them because the parts I bought, even though they looked identical, had the same part number, and Amazon SAID they fit my model #, they had the contacts in the wrong places, making the connection impossible.

So, the answer is yes. The ONE little grey door switch that was the *correct* replacement configuration must have done the trick. 

My advice is be very careful to match the part visually when purchasing from Amazon, if you go that route.

Not sure why I went with Amazon, but maybe it is best to use an appliance shop, online or otherwise.

[Jonathan Ayala]

On 6/5/2020 at 7:19 AM, swataz said:

There are two parts to this answer.

I was only able to replace one of them because the parts I bought, even though they looked identical, had the same part number, and Amazon SAID they fit my model #, they had the contacts in the wrong places, making the connection impossible.

So, the answer is yes. The ONE little grey door switch that was the *correct* replacement configuration must have done the trick. 

My advice is be very careful to match the part visually when purchasing from Amazon, if you go that route.

Not sure why I went with Amazon, but maybe it is best to use an appliance shop, online or otherwise.

ahhh ok i got you. i normally go with oem parts but i have been thinking lately to go with aftermarket for those switches. but thank you for responding i greatly appreciate it. 

[Skyhilljim]

Hey Samanera. Do you have that part number?

[ABA Tech]

7 hours ago, Skyhilljim said:

Hey Samanera. Do you have that part number?

https://www.supco.com/web/supco_live/products/ES16802.html

You can use these. They're generic and they will be either normally open or normally closed depending on what terminals you use (a microwave will normally have two switches that are normally open and one that's normally closed). Just cut off the terminal you're not using to make sure it's not touching anything you don't want it to touch. 

 

[Jrasss57]

This a frigidaire issue.  They denied it was their problem the first time it happened to me. My dealer fixed it and now a year later frigidaire has finally admitted it. However, they are really slow in getting the parts to the dealer. My advice is call frigidaire consumer complaint line with your model number and tell them to fix it or get you a new one.  Frigidaire is completely at fault and the dealers and consumers are getting the shaft.

[Kera]

How were you able to convince them to supply you with the part? At no cost?

[Kera]

I’m having the same issue with this same model. After warming something in the microwave I swung open the microwave door and the power went out, tripping the breaker. I turned the breaker back on and the microwave came back on for a moment, I went above the microcars to the plug, jiggled it a bit and the lights flickered, so I propped something against it to try and keep the microwave on.

About another hour later I used the microwave again and the same things happened again, microwave went off- breaker went off and the microwave stayed dead even after I giggled the plug. 

I don’t even know where to start. I do t want to call a repair person just yet.

 

any suggestions?