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Yup, any time I see an iced evaporator, first thing I do is mark the clock. Then continue with preliminary inspection and gathering model/serial info.

I've definitely seen dtfd's cause the defrost timer issue as previously described. It terminates the instant it starts, so to speak.

But, for what it's worth, I've seen fan behavior just like this which was caused by residual ice in the core of the evaporator, which blocked air flow through the coil and so the only other place for the air to travel through was through the "weaker" fan, fighting against it. (Note that weaker doesn't necessarily mean a defective fan, but in this scenario, one of them will dominate the other.) Pull the blade assembly off of the slower fan and see if the motor comes up to speed. And get a -bright- lite and make sure that coil is clear all the way through.

Originally Posted by cjpwalker

Skipping defrost coupled with strange fan behavior sounds more like a defrost terminator/fan delay switch problem to me. The epoxy seal on those breaks down over time and they fill with water.

Yea I've witnessed very odd voltages when water gets in switches. You will get like 98 volts or 66 or somewhere inbetween , and the fan runs slow

and like said above .... the case might just shock the hell outta you

oops, takin this new drug called DAMMITOL!

I concur w/cjpwalker. Sounds like a bad defrost ini/ter. control. grabbit an growl!

I agree with cj walker....check the defrost initiate/terminate stat..

Originally Posted by jpsmith1cm

not if you then take a few minutes, close off the king valve and pump the unit down to start to defrost it....

Lol, I do this too but it still seems like time goes extra slow waiting around for the clock to move or not move...

Originally Posted by Dchappa21

This is the first thing I do now as well.... That 5 minutes feels like 30 waiting to see if it moves.

not if you then take a few minutes, close off the king valve and pump the unit down to start to defrost it....

[QUOTE=jpsmith1cm;14249761]Simple test.

BEFORE you touch the timer wheel, take a sharpie and mark the inner wheel of the timer inline with the time arrow.

Wait 5 minutes.

This is the first thing I do now as well.... That 5 minutes feels like 30 waiting to see if it moves.

One note I'd add here is I had a tooth strip out so it would hang up in the same spot every time. It took me tearing the timer out of the case to see it. This isn't hard to do, just takes a minute to take a peek.

I don't know about "great" here.....

The first thing I like to do when suspecting defrost timers, is grab a sharpie and make a tiny mark around the minute knob on the timer. (to mark current time/position)

I do this before I even so much as touch that knob.

Then I come back in ~5 minutes and see if the knob has advanced any time.

If it has moved -> Good. Advance it to the next defrost cycle and move on to other things.
If it hasn't moved -> Bad. Replace timer.

(What this checks is both the timer motor itself, and also the clock gearing which can get hard to turn after years of dirt, and eventually lock up.)

As has been stated, it sounds like you replaced a timer that was maybe fine because the Defrost Term switch is bad and threw you for a loop. Chalk it up to experience and don't do it again.

EDIT : JP - great minds think alike?

Originally Posted by akelesis

Just a thought this is all too much to take on right now gotta read and understand this stuff i dont want to cost a customer another unnecessary cost. how do i know that a defrost clock is defective?

Simple test.

BEFORE you touch the timer wheel, take a sharpie and mark the inner wheel of the timer inline with the time arrow.

Wait 5 minutes.

You'll know.

Attachment 310871

Originally Posted by akelesis

Just a thought this is all too much to take on right now gotta read and understand this stuff i dont want to cost a customer another unnecessary cost. how do i know that a defrost clock is defective?

Start Reading

You get the site, you walk around and look at the eqipment, then you write down the make, model, and serial number.

Is it in refrigeration or defrost, then from that you troubleshoot.

You found a frozen coil, you try to de-ice it by initiating defrost, you find it terminates upon initiation.

what type of clock?

Just a thought this is all too much to take on right now gotta read and understand this stuff i dont want to cost a customer another unnecessary cost. how do i know that a defrost clock is defective?

With experience your boss would be right, and you could have been in and out of there sooner. Over time you will tend to see the same failures over and over.

But -- that's boring, and troubleshooting can be fun if you have really good knowledge of how the thing works. Check out page 40, the 2nd diagram of the attached manual.

Attachment 310851
The "DTFD" allows the fans to run in normal operation. When the unit switches to defrost and heats up, the 'DTFD' will switch contacts, opening up the fan circuit (that is already dead from the clock being in defrost mode) and closing the circuit to "X"

"X" powers a coil that throws the defrost clock back into normal run mode early. "X" is powered on the other side off of the "3" terminal which drops out as soon as the timer switches, so that coil is only ever energized for a split second. It will actually burn up if it ever sticks on.

Refrigeration starts, and once the coil cools down, the "DTFD" switches back again closes the fan circuit.

If that DTFD is shorted it can pass power to X all of the time and cause defrost to skip. Because your fans run through it as well you can see some strange voltage related behavior there, too. You can also get a nasty shock off of the case of that evaporator.

When that happens, I immediately disconnect X wire and try again. If it is the termination/delay that is bad, defrost will proceed as normal after X is disconnected.

Booo dont tell me that. that sucks

If it "skipped past" defrost when you manually attempted defrost, then you most likely have a bad defrost termination/fan delay. The old clock was probably OK.

ok when i got there the coil was frozen so i was advised to turn on the defrost i tried. first few times it skipped past it. my boss quickly said ok replace that so i did. i finally got it into defrost after like 3 tries. thats why i replaced the defrost clock.

*note* i just came out of school like 6 months ago passing my intermediate so i got jumped into refrigeration stuff i know the basics by reading it but actually seeing it in the field is a whole different can of worms. i dont often work on freezers but when i do i tend to be ok. but this will take time. i know enough to be left alone. and i was told doing everything by the book will make ur job a lot longer then it actually can be. my boss told me i should have been out of there in 3 hrs. still a lot to learn.