My service man replaced the defrost cycle timer and the relay (timer was definitely broken, relay was highly suspect) but the freezer fan still has no power so freezer will not chill adequately despite very cold coils. We need a wiring diagram to follow to finish ths job off. I have a Traulsen URS48DT unit.

it is not defrosting. timer ,element , limit switch maybe issue. find defrost timer advance it see if compressor and fan quit running. when you advance this it should start defrost mode, which turns on the heater, which stays on till limit switch opens or timer advances, most are on 12 hour cycles

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DEFROST PROBLEM
The evaporator coil behind the cover on the back wall inside the freezer will ice up under normal conditions. Every 8 to 10 hours for around 20 minutes the defrost timer (or in most newer models the electronic adaptive defrost control) will turn the defrost heater on to melt the built up ice. There is a defrost thermostat which prevents the heater from overheating the freezer by breaking the heater circuit when the temp reaches close to 32 degrees F. The entire cooling system shuts off during the defrost cycle and starts back when the timer advances through the cycle.

If this ice is not melted it will continue to build up until the air can't flow over the coil to circulate the cold air through the freezer and into the fridge. The temperature change in the fridge is usually noticed first followed by the freezer.

If the defrost thermostat is bad, it can prevent the heater from coming on OR it won't turn the heater off when it gets too warm. It is clamped to the evaporator coil at the top to sense the temp. If it appears to be misshapen it is bad.
With an ohm meter it should show continuity when cold and none when warm.
You can also bypass(disconnect the two wires plugged into it and twist them together) the thermostat to see if the heater comes on then. If it does then you know the thermostat is bad and needs replaced.

The defrost heater is located on the evaporator. It is in a tube which is at the bottom and can also go up the sides of the evaporator. On some types you can see a burnt spot if it's bad. With an ohm meter it should show continuity from end to end when disconnected from the wiring in the freezer. You can also test the wiring for voltage when it's in the defrost mode.

If you have a defrost timer you can test it. It can be located under the fridge behind the kick panel on the front. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer because that means the timer is not running. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.

If you have an adaptive defrost control instead of a timer, replace it if the heater and thermostat test good. It is located in the fridge with the controls in some models and on the back in others.

Hi Guys, I tested fan removed(to 240vlts) neg- pos to wires+earth to mount bracket, and found to be working, reinstalled and found power - active to both wires??fan cut out (defrost mode)activated by timer control, my timer control ( bottom rear near motor) has a knob, so i turned it and fan started,continous turning knob ran thru all cycles defrost,fan start, etc: obviously timer control was faulty, To save frozen goods , i set control to run and installed a power point timer to cycle freezer till new switch arrives, taking the place of faulty controller...

. Cut everything off for a few minutes then turn it back on and listen for a click from the compressor relay as the compressor tries to start.
Is the compressor motor running.If no check starter/overload relay.
Check to see if the condenser fan at the back underneath near the compressor is running. If no check fan.

Are the condenser coils near there warm or room temp. should be warm


The evaporator coil behind the cover on the back wall inside the freezer will ice up under normal conditions. Every 8 to 10 hours for around 20 minutes the defrost timer (or in most newer models the electronic adaptive defrost control) will turn the defrost heater on to melt the built up ice. There is a defrost thermostat which prevents the heater from overheating the freezer by breaking the heater circuit when the temp reaches close to 32 degrees F. The entire cooling system shuts off during the defrost cycle and starts back when the timer advances through the cycle.

If this ice is not melted it will continue to build up until the air can’t flow over the coil to circulate the cold air through the freezer and into the fridge. The temperature change in the fridge is usually noticed first followed by the freezer.

If the defrost thermostat is bad it can prevent the heater from coming on OR it won’t turn the heater off when it gets too warm. It is clamped to the evaporator coil at the top to sense the temp. If it appears to be misshapen it is bad.
With an ohm meter it should show continuity when cold and none when warm.
You can also bypass the thermostat to see if the heater comes on then. If it does then you know the thermostat is bad and needs replaced.

The defrost heater is located on the evaporator. It is in a tube which is at the bottom and can also go up the sides of the evaporator. On some types you can see a burnt spot if it’s bad. With an ohm meter it should show continuity from end to end when disconnected from the wiring in the freezer. You can also test the wiring for voltage when it’s in the defrost mode.

If you have a defrost timer you can test it. It can be located under the fridge behind the kick panel on the front. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer because that means the timer is not running. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.

If you have an adaptive defrost control instead of a timer, replace it if the heater and thermostat test good. It is located in the fridge with the controls in some models and on the back in others.

If you need help finding your model number see here> http://www.appliancepartspros.com/modelnumber_locator.aspx

To locate your timer, motherboard, control or adaptive defrost control , enter your model number and search for the part or post back on Fixya.
http://www.searspartsdirect.com/partsdirect/index.action?psid=26129238&sid=PSx20071217x00001a

Hello there:
first make sure that the back of the unit is clear of any dirt or obstructions
also make sure that the food is not stacked up so high that the air cannot circulate also you may want to check the temperature setting if the unit does not respond to a lower setting your refrigerant level may be low or than you will have to have the temperature controle thermistor serviced or replaced

Make sure the fan in the freezer is running circulating the air.
How to check everything
http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php

If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.

check defrost timer, defrost heater, defrost thermostat. In most newer models the timer has been replaced by an electronic control board. If the heater and thermostat are ok it’ll be the control.

You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.

How to check everything
http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php

If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.

check defrost timer, defrost heater, defrost thermostat. In most newer models the timer has been replaced by an electronic control board. If the heater and thermostat are ok it’ll be the control.

You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.


Your evaporator coils frost up in normal use and every eight hours or so the entire unit shuts down and the defrost heater comes on to melt the frost. This cycle last about 20 minutes. The melted frost drips into a drain pan and through a drain tube to the drain tray under the freezer/refrigerator where it's evaporated by the condenser fan.

Normally, freezers have electric heaters that are energized during the defrost cycle. Once out of the defrost cycle, the refrigeration system comes on but the fans do not. This allows the evap to cool off and to prevent circulating warm air from the heaters. This is controlled by a fan delay switch. It is a small, round device that can have 2, 3, or 4 wires going to it, depending on the manufacturer. It is usually clipped on to the end of the evap coil on one of the "U" bends, near the top, inside one of the ends of the evap. Usually where all the electrial components are located. It come in several variations, but it's main function is to prevent the fans from energizing too early. Usually does not bring fans on till evap hits 20 or so degrees. Check this out and get back to me.

Could be a couple of things. First measure the resistance of the defrost heater that is mounted on the evaporator coil in freezer compartment. Make sure to disconnect the power from freezer first. The disconnect the defrost heater and measure with ohm meter. It should measure in the 20 ohm range. If it measures as "open" replace the coil.

Next suspect is the defrost timer mounted in the front of the compressor compartment. If the heater coil is OK, I'd just replace the timer. It is tough to test.

Finally, there is a defrost termination sensor mounted on the top of the defrost heater that shuts off the defrost heater when it reaches a high temperature. If the coil tests OK, and you are going to replace the timer, you may want to replace the sensor too. It is awkward to test, the temperature of the sensor needs to be be below room temperature to close. The cost of the sensor is low enough that you may not want to replace the timer, then test the system, and then have to go back in to replace the sensor later.

It might be the timer motor, if it doesn't run. neither does the timer. Easily replaceable and cheap. good luck. John