rtv

Found 1 Result for rtv.

Showing 1 to 1.

1. Electric Heaters
The simplest and most popular electric heater is a heating coil connected to a line cord. A more'complicated type is shown in the exploded view in Fig. 5-5. This is a room heater with a two-speed fan and automatic temperature control. It uses two finned heating elements and a switch for a selection of one element or two. A control lever regulates the temperature. When set to the extreme left, the unit is off. A slight movement to the right turns on a light to indicate the unit will go on when the thermostat calls for heat. The unit automatically maintains the desired temperature in the area it is capable of heating. Many models similar to the one shown have a tip-over switch to automatically shut off the heat if the unit is tilted more than 30 degrees from the upright position. The fan operates at 2100 and 2700 rpm. The unit is rated at 1650- 1200W, 120V, 60 Hz, and delivers 5600 BTU / hr. Thermostat Calibration Although many space heaters have nonadjustable thermostats, the thermostat used in this particular unit is adjustable. The thermostat uses a bimetal leaf with two adjusting screws. Access by removing the two expansion-clip plugs located underneath the shell. The thermostat also has a back contact to activate the light. This contact is nonadjustable. The adjusting screws have a slotted head to accept a screwdriver. When making an adjustment, turn the adjusting screw only a quarter turn at a time and then remove the screwdriver as the slight pressure of the tool will give a false reading. Use a continuity tester, VOM or wattmeter when making any adjustment to the thermostat. To adjust for room temperature, slide the temperature-control knob slowly to the right until the circuit is complete. The temperature point on the faceplate should be within 10° below room temperature. If the variation is more than 10° below room temperature, set the control knob within this range on the faceplate and turn the thermostat adjustment screw clockwise to open the circuit. Should the control knob go past room temperature on the faceplate, turn the thermostat adjustment screw counterclockwise to move the adjustment down to room temperature. After each adjustment, return the control knob to the off position and repeat the circuit test. Make the differential adjustment after the room-temperature adjustment. (See Fig. 5-6.) This adjustment varies the time lag of the bimetal leaf. The wider the gap, the longer it will take for the bimetal leaf to close the circuit. Move the control knob to the right and left so the thermostat contacts just open and close. Note the temperature difference on the faceplate between the on and off positions. This is the differential. Turn the differential adjustment a quarter turn at a time to limit the differential to approximately 5°. Turning the screw clockwise decreases the differential; counterclockwise increases it. Do not adjust the differential too small. This could cause a continuous closed contact or erratic on-off cycling. The back contact for the light can be tested with a VOM at the thermostat terminal leads. Servicing The Units To disassemble, remove the two screws securing the nameplate to the shell. Pull the temperature control knob from control lever. Some lubricant may be required so the knob slides freely. Remove the control lever; it is secured by a nut. Note the flat on the shaft for positioning the control lever. Next, take out the two screws located directly above and below the control shaft. The screws on each side should not be removed. Remove the screws securing both switches to the shell and the outer screws securing the rear cover to the shell. The rear cover with all component parts can now be lifted away from the shell for replacement of parts and testing. To replace the thermostat, remove the two screws from each side of control shaft which secure the thermostat to the light bracket. Disconnect the wires from thermostat. The switches require special consideration. With the element switch on low, the 1150W element circuit is complete and the switch is open. Turning the switch to high adds the 450W element. The fan switch employs a resistor to reduce the fan motor rpm. On high the switch is closed. Both switches can be tested with a VOM. A complete circuit indicates a closed switch. If the switches are not isolated from the circuit, a resistance reading may appear on an open switch. During assembly the switches are positioned in the shell with the terminals towards the bottom. The motor can be electrically tested between the motor-lead connection on the fan switch and the splice lead at the element switch. Replace the motor as an assembly (less fan). Remember to oil the bearing felts when servicing the unit. The 1150W element (upper element) is used whenever the heat is on. The 450W element (lower element) is added when the element switch is on high. The elements are marked on the end for identification. Remove as follows: a. Disconnect the wires from elements. b.  Remove the element retainer and slide the elements out. c. Check for broken or cracked ceramic insulators. d.  Use Silastic 732 RTV or other plastic sealer on the element ends and ceramic insulators to prevent rotation and a vibration rattle. The tip-over switch is a safety switch used to open the heating circuit when the unit is tilted over 30 degrees from the vertical. The pendulum on the switch must be free to move and the contacts must close when the pendulum is in the upright position. Troubleshooting No heat means an open in the element, thermostat, or tip-over switch. Make individual continuity checks. If only the low-heat function operates, check the low-heat element and switch. No light would lead one to suspect the lamp (filament and socket) and the back contact on the thermostat. A dead fan involves the motor or fan switch. The former may have an electrical fault or it may be the victim of seized bearings. If the room temperature is too low, look to the thermostat adjustments. The stat may be adjusted too low or the differential may be too wide. A dead fan can also be the culprit. Of course, a low-heat complaint assumes that the room is not too large for the heater. Too high a room temperature means that the thermostat is too high or that the differential is too small. Noise can originate in loose motor mounts, contact between the fan and shell, or a loose element.
http://www.fun-home-projects.com/electrical_projects/​repairs/​electric_heaters.html

Search Here:

Menu:
Home
Collecting
Crafts
Electrical Projects
Energy Savings
Hobbies
Home Ownership
Household Repairs