Microwave quite heating. Tried cup of water, but not heating. The fan is running but sounds abnormal. The lights are on and the turntable moves.

This is normal. Kenmore microwaves will stay running with fan and light on for a short time after food is cooked. The reason is to air out the microwave after cooking. Things like pop corn, Bacon etc. have strong smells after cooking. The ventilation helps to remove odors.

SOMETIMES A DOOR SWITCH GOES BAD AND BACK FEEDS POWER THAT RUNS THE FAN AND IF IT HAS IT SOMETIMES THE TURNTABLE TOO SO YOU HEAR THE FAN RUN ALL THE TIME BUT TYPICALLY IT IS NOT HEATING. YOU COULD PUT A SMALL CUP OF WATER INSIDE TO SEE IF IT IS HEATING, PROBABLY BAD DOOR SWITCHES OR BAD CONTROLLER.

Is it still heating food properly? You can perform a basic test with a microwave safe mug or plastic cup of water. It should be boiling or too hot to touch within 1 to 2 minutes. Be careful not to overheat the cup if plastic and use extreme caution when touching or removing it from the microwave.

If it is not heating properly then the magnetron may be faulty and unit should be replaced.

Can you tell what specifically is speeding and slowing? Is it the turntable or the humming sound of the unit itself? Many microwaves vary their intensity in order to heat/cook evenly and that will vary the pitch of the sound you hear and sound like it is speeding up or slowing down. If the turntable is slowing and speeding up then there may be a bad motor and the unit should probably be replaced.

If the unit is heating adequately and the turntable speed is uniform then what you may be hearing is simple power cycling and/or fan noise.

Only trained and certified technicians should attempt repair of microwaves due to the hazards of high voltage and microwave radiation leakage if parts are not replaced properly. Although you can have a microwave repaired the cost may be equal to, or higher than, the cost of an equivalent new unit for a 900w microwave.

When you hit "Start" to microwave, do the inside light, cooling fan, and turntable all come on?

Any unusual noises? Is it louder or quieter than usual?

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

Post a new help request with the answers to these questions as well as the full model number from the tag on or in the unit.

A full Sears/Kenmore model number has 3 digits, a dot, then 8 more digits, such as ###.########

first suspect is the inverter board (power) and magnatron a distant second----in either case the part involved unless an expensive unit is pricey.

Suggest you pull the plug out, remove outer cover and place a cup of water into the micro. Set power to minimum then switch on and take note if the fan works or not. If not, switch off immediately and have it replaced(magnatron will burn out if left to run without fan.)

Possibly the light bulb has blown, which has blown on a track on the board which has taken out the turntable motor and the fan. Also, there could be a problem with the door switch.

I don't like to pass on your problem but it sounds very much like either the high voltage supply ot the magnetron has bit the dust.
Either one would make the repair marginal at best.

This is apparently not a very good unit, many microwaves jsut kind of fade away as their magnetron emissions decay.

This one seems to have a bad rep. look at this link:

http://www.fixya.com/search/p489218-ge_xl1800_1100_watts_microwave_oven/not_heat

Sorry, have owned a lemon or two myself.

It may be a noise coming from the turntable motor or stirrer motor, if so equipped.

If it's not too loud, I wouldn't worry about it unless it gets louder or you get further symptoms.