My West Bend 900 watts microwave motor is running when the door is open. Is this safe?

Damaged door switches will do that.

This fault is due to faulty relay in the PCB assembly,it is responsible to switch on & off with the command key pad operations.

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.

Your best bet is to contact West Bend directly. Here is a link to their support contact page
West Bend Kitchen Appliances Celebrating 100 Years Contact Us Support

Hi TIM BARR,
according to the user manual you should reset the circuit breaker.

See page 17 on manual:
http://www.jensenheavyduty.com/downloads/dl/file/id/186/mw900bk_owners_manual.pdf

You can get the manual from West Bend here.

how do i set my hamilton beach 900 watt microwave to 50% power

Your 3000 watts should be enough. An average freezer will need 800 or 900 watts.