Whirlpool Microwave Not Heating


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Old 05-25-23, 11:34 AM
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Whirlpool Microwave Not Heating

Hello all,

I have a problem with my 2019 model Whirlpool over-the-range microwave not heating up food or liquid. Everything else seems to run fine except the heating. Model is wmh32519hz3.
I have tested the diode, magnetron and capacitor which all pass the tests according to Repair Clinic's testing methods. What else could it be? The transformer shows no signs of burn damage or smell. I have not checked the door switches yet.

Thanks!
Grant
 
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Old 05-25-23, 06:27 PM
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You need to check for 120vac on the primary side of the transformer when heating.
That's the low voltage side of the transformer.
Finding or not finding that voltage will dictate the direction to check.

BE CAREFUL - DANGER - HIGH VOLTAGE INSIDE
 

Last edited by PJmax; 05-25-23 at 08:11 PM.
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Old 05-25-23, 06:53 PM
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Yes I have the service tech sheet but it's W11279376A. It was in a sealed bag.
 
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Old 05-25-23, 07:44 PM
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I removed the transformer and measured resistance across the secondary winding lead and to ground (the mounting holes). I get only 0.3 Ohms. Apparently it should read 35 to 100 Ohms. Has my transformer shorted?
 
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Old 05-25-23, 08:13 PM
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Interesting.... same tech sheet under two different numbers.

You'd know if your transformer was shorted. You'd get a bang.
I'll check it connected in the unit. If there is 120v on the primary and no heat... I know it's an HV problem.
Pretty new unit for HV problems.
 
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Old 05-26-23, 11:28 AM
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So reinstall the HV transformer, plug microwave in to an outlet and run a cycle. Then check for 120V??
 
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Old 05-26-23, 02:15 PM
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Yes....correct.
 
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Old 05-26-23, 05:57 PM
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Ok I'm getting 115 VAC when touching my multimeterleads to the two wire terminals coming off the primary winding.
It seems that my HV transformer is good.
 

Last edited by Roesner; 05-26-23 at 06:08 PM.
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Old 05-26-23, 06:20 PM
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That leaves the HV diode, HV cap, the magnetron.

The transformer has two output windings.... the filament winding which is shown as red and black.
The high voltage winding is white to ground.
 
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Old 05-26-23, 06:24 PM
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The diode, capacitor and magnetron pass the continuity tests. Capacitor measured 1.09 microfarads and it's rated at 1.05.

I don't know what else to check.
 
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Old 05-26-23, 06:36 PM
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Do you know the sound a microwave makes when it ramps up ?
When it first starts the HV is quiet and after a few seconds you can hear the transformer strain as the magnetron heats up and draws power. Do you hear that ?

A magnetron can check good electrically and be bad.
A cracked magnet is a rare but possible problem.

More on the magnetron......... willie method
 
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Old 05-26-23, 06:58 PM
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Yes, after about 4 seconds I hear a light buzz sound. Almost like a muted residential A/C compressor kicking on. Then it lasts for another 10 seconds and fade away.

I should have mentioned in my first post that the microwave started making a louder hum/buzzing noise whenever it failed to heat food.

When he refers to a "magtube" does he mean the magnetron? Also, he says to unplug the two wires to the magtube. These are the thick red and black insulated wires connecting the magnetron, yes? I assume you unplug the microwave, discharge the capacitor, disconnect the two wires, then plug it back in, and then run a cycle?
 

Last edited by Roesner; 05-26-23 at 07:55 PM.
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Old 05-27-23, 01:37 AM
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Yes... some sound like a light buzz.
When the filament heats up in 3-4 seconds it starts drawing heavy power.
If you have it set in normal or HI heat.... that buzz should not stop.
If it's stopping in 10 seconds.... that's pointing to a bad magnetron.

If allowed to continue running... does the buzz start again ?
After safing off the area and killing power....check the magnetron fins..... are they extremely hot ?
There should be a fan blowing thru the fins. If not and it gets too hot.... the thermal sensor on the mag will shut down the transformer until it cools off.

The magnetron is nothing more than a high power high frequency tube

 
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Old 05-27-23, 11:25 AM
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I ran the microwave for 60 seconds and the light buzz noise came on after a few seconds and then faded away like before. But it stayed away for about 45 seconds. I could not feel any airflow through the magnetron's heatsink. There is a plastic duct that is on one side of the magnetron and it connects to the blower fan at the top rear.
 
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Old 05-27-23, 11:31 AM
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So was the case/fins of the magnetron warm/hot ?
It sounds like it may be overheating.
Was that blower working ?
 
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Old 05-27-23, 04:14 PM
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The magnetron fins/case did not get warm/hot after 60 seconds. They felt like they were at room temperature after the cycle.

The blower at the rear is working fine. I assume it pulls air through the magnetron via the duct and exits through the blower.
 

Last edited by Roesner; 05-27-23 at 06:35 PM.
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Old 05-28-23, 09:23 AM
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I'll probably just replace the magnetron.
 
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Old 05-28-23, 02:29 PM
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I would agree....... WPW10693025.
Magnetron
 
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Old 05-29-23, 04:54 PM
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Alright! So I swapped out magnetrons with a new one and it heats up once again!

I did notice that the fins and case become very hot on the new magnetron even after only a 60 second cycle. Power is programmed on 100%.

Is this normal?
 
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Old 05-30-23, 12:57 PM
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No.... it's not normal. The mag should not get excessively hot.
Most microwaves have a small blower cooling the mag.
I only see the main blower and a series of baffles in yours.

I'm not totally sure how that cooling system works. It would appear by duct design that that the main blower is supposed to draw air in from/across the tube to cool it. The schematic doesn't show the blower running during microwave operation....does it run ?

There are unusual duct pieces shown. You're going to need to check for a clear airflow path.
make sure the airflow pieces are in place.


 
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Old 05-30-23, 07:43 PM
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Yes the blower works fine. It moves a good amount of air out the top when the microwave is running. It blows into a small exhaust duct hidden in the cabinet above the unit and exits to outside the house. There is no fan dedicated to the magnetron just like your schematic shows. Maybe that's why it failed already lol.

I mean if you left your finger on the fins long enough you would be burned. The service manual mentions the mag tstat opens at 275 F and closes at 203 F. Or maybe the other way around. What does that mean?
 
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Old Yesterday, 05:04 PM
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Correct.... no fan dedicated to the microwave.

1) as asked..... does the main blower run when the microwave runs.
2) you need to check for air going into the mag tube. Try using a little smoke.

It would open at 275f and reclose at 203f. That's pretty hot.
I don't know if that's too hot. I've never needed to check operating temp.

 
 

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