Thanks for the detailed description, it helps a lot. A Kenmore 790. model was built by Frigidaire (Electrolux), and the 790.74… series is a gas range. That changes the likely causes. A gas oven has very little wiring inside the oven cavity, so a “wire touching a hot wall” is possible but not the first thing we’d suspect.
Safety first
- If anyone smells gas (a rotten-egg smell), turn off the range, don’t use any switches or flames, and call the gas utility.
- Until you know the cause, ask the tenant not to use the oven. Make sure there is a working carbon monoxide alarm in the home.
- Before removing any panel, unplug the range (it has a 120 V cord for the igniters and controls) and turn off the gas valve behind it.
Most likely causes, in the order we’d check them
- Something stored in the broiler drawer. On most Frigidaire-built gas ranges the bottom drawer is not a storage drawer, it’s the broiler. The broiler gets hot whenever the oven is on. Tenants very often keep plastic containers, cutting boards or oven mitts in it. This is the number one cause of a “burning plastic” smell we see on these ranges. Pull the drawer all the way out and look for melted plastic on the pan and on the floor of the drawer cavity.
- Melted plastic or spilled food inside the oven. Remove the racks and check the oven bottom. On this design the bottom panel usually lifts out after removing two screws at the back. Look for a melted utensil, a plastic bag or a big grease spill on the burner cover. Burnt grease smokes heavily from the vent the first few minutes after startup and then settles down.
- Spills down the oven vent. The oven exhausts through a vent under the rear cooktop burner or at the backguard. Boil-overs from the cooktop, or a plastic lid left on the back burner area, can collect in that vent and cook every time the oven heats up. Check under the rear grate and the vent cover.
- Wiring or connectors near the oven igniter. The oven igniter (a glow bar near the burner under the bottom panel) runs extremely hot. Its leads have high-temperature insulation and ceramic connectors. If a lead has come loose, been re-routed during an earlier repair, or a cheap replacement igniter was installed with standard connectors, the insulation can melt and smell like burning plastic. With the power off, remove the bottom panel and look along the igniter wires for brown, cracked or melted insulation. Any damaged wire must be replaced with high-temperature appliance wire and connectors, never ordinary hardware-store wire.
- Insulation or a factory protective film after a part was replaced. If anything in the oven was replaced recently, a small amount of smoke for the first one or two heat-ups can be normal. On an old range with no recent work, this is unlikely.
About the cooktop burners that won’t click to light
That doesn’t tell you the age. It’s a separate system: spark electrodes, their wires and a spark module. The usual cause is a cracked white ceramic electrode or a burner cap that’s dirty or misaligned. If no burner clicks, or one clicks all the time, it is often the spark switch on the knob shaft getting wet from a spill. These are inexpensive parts.
Quick summary for your visit
Check the broiler drawer, then the oven bottom, then the rear vent, then the igniter wiring under the bottom panel. If the smell continues after all four are clean and the wiring looks good, have a local appliance technician check the range before it goes back into regular use.