It doesn't sound like your fridge uses an adaptive type timer, so you have either a Type 1 or Type 2 timer.

If it's Type 1, the timer motor is spinning any time the unit is plugged in. Compressor duty cycle has no affect on the defrost cycle - it powers up every xx hours in real time. In this case you'll expect defrosting to occur like clockwork every 16 hours (give or take). Unless your fridge is an older model or a small compact, this probably isn't the timer you have. An easy test would be turn the cold control all the way off, wait a few hours, then see if the timer's run indicator has advanced. If not, then you have a Type 2.

Type 2 is an improved version of Type 1. This timer works essentially the same, but instead of cycles regulated by the clock, it activates (counts down) only when the compressor is running. Therefore it's cycles are based upon cooling run-time, which makes sense when you think about it. Could save a lot of wasted energy over the life of the unit. Not to mention prolonging the life of the defrost components.

With this type of timer you can't predict when it will defrost, since it's dependent on parameters other than real time. If it's only coming on once every 24+ hours, I'd say that's pretty much normal. If interior temp is normal and has remained steady over time, you can assume the defrost system is OK.

Originally Posted by: rohit1st

Hi - I am having a similar problem with my Whirlpool top freezer unit.

1. Timer is not advancing from cooling to defrost. When I manually move it to defrost, it does move for ~20 mins and then get into cooling cycle, but then, it just stays there. I replaced the timer and got the same behavior.

2. When I put the timer in defrost mode manually, at times the heater comes on, and on other times it doesn't.
For #2, I am thinking that the bi-metal thermostat is not working properly, so I am planning to replace it.
For #1, I am not sure if its related to #2 or it has something to do with something else.

Any help is appreciated!

The only thing I can determine for sure is that your heating element is OK. Symptom #1 sounds like classic timer failure, but the new part should have corrected that. When you say the timer will not advance in cooling mode, did you observe this over several compressor cycles? Most likely you have a timer that only advances when the compressor is running, so give it some time. If the timer is, indeed, unresponsive, I would look at the cold control (thermostat) next.

AC power to the timer and defrost heater is supplied through the cold control. They routinely wear out, usually due to pitted or burnt electrical contacts. When this happens symptoms can vary from total system failure to intermittent operation. Remove the freezer's back panel, which covers the evaporator coils. Inspect the wiring for loose or damaged connectors. If all looks good, close the door and allow the freezer to cool down the normal temp. Proceed to the next step.

Advance the timer until it clicks into defrost mode. Wait about 5 minutes, then open the door and verify that the heating element is hot (be careful not to burn yourself). If not, try tapping the cold control and see if this brings it up. If so, replace the control. Go ahead and replace the defrost thermostat as well. You already have the evaporator exposed, so it will be a quick and easy job. All 3 defrost control elements will now be factory-fresh, and should insure reliable operation for a long time.

One more note: Whenever possible, install geniune OEM replacement parts. You can find cheaper substitutes, but don't be tempted. Quality, duralbility, and fitment may be questionable. I've never had any problems with parts that come in a factory box or bag. You get what you pay for.