Microwave not heating unless exhaust fan is on high

A significant failure in a 7-year old microwave usually means replace rather than repair.

Check to see if there's a relay providing power to the fan. If there is, the contacts might be sticking in the closed position. Assuming that this is an over-the-range unit, disconnecting the vent fan completely might not be a good idea as heat/steam from foods cooking on the range would more likely damage the microwave.

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There are three common issues, the magnetron "heats food" a cracked high voltage diode, a shorted high voltage capacitor.

Hi,

Here is a tip that will help you to figure out what is wrong with your Microwave Oven....

Microwave Oven Basic Troubleshooting Tips

heatman101

If it goes dead for a while during or after cooking then comes back on, the magnetron is probably overheating and causing the magnetron thermostat to open.

Then when it cools, it closes the circuit and allows power through again.

An overheating magnetron can be due to:

• operating oven without cover(s) in place
• wrong magnetron installed in oven
• an old or otherwise failing magnetron
• cracked magnetron magnet
• improper power line voltage (should be 110-125VAC)
• foods low in moisture (popcorn & bacon, e.g. - add 1/2 cup of water in rear oven)
• failed or inoperable cooling fan or hood vent exhaust fan
• deteriorating foam weatherstripping seals in air ducts or on outside cover
• blocked air vents (dust, animal nest debris, insufficient free air space behind & around oven, etc.)
• clogged or greasy charcoal filter or grease filter
• blocked duct in hood vent exhaust

We have a sound clip of what a microwave should sound like when the cooling fan and high voltage section are operating here.

It is vital that the cooling fan runs, or the magnetron will be destroyed. Repeated shutdowns like this are endangering the magnetron, assuming it's not bad already.

Your owner's manual will cover checking the filters and will cover warranty terms. The magnetron may still be covered.

If for some reason you don't have your manual, you can download it here.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

William E. Miller
prototech@usa.net
http://www.microwavedisplay.com

Hi,
Here is a tip that will help you to figure out what is wrong with yourMicrowave Oven....

Basic Microwave Oven TroubleshootingTips

heatman101-==-

If it is a loud buzzing noise it is either the diode or magnetron. Working with the high voltage of a Microwave oven I would never recommend anyone other than a trained professional to attempt this repair.

If it operates as normal but items don't seem to get hot it probably is a Magnatron failure (microwave producer). More times than not the repair / replacement of a Magnatron these days is not worth the investment, especially if the microwave is 4 years old or older ! You should be able to replace your microwave with a similar featured microwave / hood for about $300 to $400. You might try a JVM1750DMWW by GE great micro/hood for about $300, includes one touch sensor cook capabilities,300 CFM vent fan,removable rack,option to turn the turntable on or off, 1000 watts of cooking power. Good luck !

the fan may be clean, may be fan bush struck thats why fan running not properly, check the internally inside the microwave oven , you should carefull inside micro wave oven very high voltage .