Walk in freezer defrost cycle question

[Maven445]

I posted this in the wrong section before maybe someone here can help me. I have a problem with a walk in freezer. The evap coils keeps freezing up, about 1-2" a week. The front freezes up really bad with soft ice on top and solid ice on the bottom. The back freezes up just on top. During the defrost when the arm first hits the pin, nothing happens. The pump down doesnt start until the second click, by then there is about 10 - 20 minutes left on the defrost. The defrost is set to 60 minutes. The heaters only stay on for a couple minutes after that. I've replaced timers before, but I dont know the actual sequence and what the terminals are associated with. Any help would be great.

[richper]

sounds like your'e in way over your'e head.Obtain a qualified repair person!!!!

[jpsmith1cm]

A good way to learn how the timer works is to remove it and examine it.

Most defrost timers are very simple and easy to understand once you see the back side of it.

[Maven445]

Thanks richper for the useful advice. I was looking to get a breakdown of the defrost cycle. From my understanding the cycle goes as follows: The defrost timer activates the cycle, the solenoid valve is denergized and the condensing unit begins to pump down, the low pressure switch cuts power to the compressor contactor, the defrost heaters are energized, once the defrost time is reached the solenoid valve is opened and the indoor fans turn on once the coil reaches 30F. I do have an understanding of how this works but I am missing some key information.

[pauls heating &]

add in the dtfd also....and heater limits

[jpsmith1cm]

Thanks richper for the useful advice. I was looking to get a breakdown of the defrost cycle. From my understanding the cycle goes as follows: The defrost timer activates the cycle, the solenoid valve is denergized and the condensing unit begins to pump down, the low pressure switch cuts power to the compressor contactor, the defrost heaters are energized, once the defrost time is reached the solenoid valve is opened and the indoor fans turn on once the coil reaches 30F. I do have an understanding of how this works but I am missing some key information.

I've gotta say that something isn't adding up here.

Please post more information about this problem. Post specifics, not generalities and vague requests for information,

[BKS60]

We cant go into detailed info per site rules but does your compressor shut down shortly after defrost cycle is initiated?

[richper]

Sorry if I offended you but, from your original post it sounded like you are not very familiar with this type of system and well what J.P. said....Dito.

[Maven445]

No feelings hurt, its just a frustrating problem. The specifics of the problem that I see is that when the defrost timer first hits the pin and I can see the arm move, but nothing happens. Meaning that the system continues to operate. I know the timer motor works, Ive watched it go through a defrost cycle. When I manually turn the timer, I feel the first click and the second click. Its on the second click when the pump down is initiated. After the pump down is initiated there are no problems with the defrost expect that it lasts 10 - 20 minutes. The clock is set to 60 minutes. It seems way to short. There is no hi limit sensor, it was an optional part not installed. There is onlt a defrost termination switch.

[Maven445]

Another problem that I've noticed which is not associated with the defrost but I believe adds to the ice build up, is that they never keep the door closed to the freezer. Its always open about 12", not wide open. The door to the freezer is inside a walk in refrigerator and one of the evaps from the walk in refrigerator blows air directly into the open freezer. How much ice build up can occur from this.

[emcontrols]

Another problem that I've noticed which is not associated with the defrost but I believe adds to the ice build up, is that they never keep the door closed to the freezer. Its always open about 12", not wide open. The door to the freezer is inside a walk in refrigerator and one of the evaps from the walk in refrigerator blows air directly into the open freezer. How much ice build up can occur from this.

Tons got to keep the door closed. Especially since you mentioned frost not ice. Frost indicates moisture infiltration in to the walk in. Fix the door problem after you completley remove any and all frost from evap coil. If you dont it just keeps coming back like the plague. As far as the timer when you manually initiate defrost by turning dial you are fast forwarding the defrost time need to let it operate automatically and then see how long the actual defrost is. but if the defrost ends before the 60 minutes it could simply be the early term sensor canceling defrost because the case got to warm before time expired.

[sprmktrefertech]

You have to start somewhere first, lets get back to the def. problem....

I'm going to assume it has electric def...The timer motor may work, but may have a problem as it hits the tripper you can check this rather easily w/ ammeter,in any event,if the clock is bad, replace it, and set-up the same as the one you just removed as a starting point usually 1 or 2 a day is more than enough depending on area.

Yes the open of doors does create a problem w/frosting but even less when the freezer is inside the cooler.

in some cases, the door to the box must be closed to close the fan ,and ,or sol.circuit.

and to be sure to check def. Term sensor/klixon that it is not kicking it out of def.

[Maven445]

I actually spoke to a supplier and he told me that it was probably the defrost termination switch, which doesnt make sense cause that doesnt affect the start of the defrost. I just wanted to get some more info on the defrost cycle. Thanks everyone for your posts.

[2wings]

When you hear the first click, are the defrost heaters energized at that point or are they energized on the second click? It sounds like the defrost timer is working correctly and you have a defrost termination swich location problem or faulty sensor, is the "X" wire hooked up in the timer? if so, try unhooking for a day or so and see if defrost completes, if so, than sensor problem.

[richper]

The system is time initated temp. terminated. The timer should advance thru unassisted.The 60 min. setting you speak of is a fail safe setting and should not be looked at as a primary defrost time.The uneven frost pattern you mention could be caused by many different things.You must do alot more trouble shooting on this system for a proper diagnoses!!

[2sac]

What brand evaporator coil is it? Heaters on the bottom only or heaters on the bottom and back? In most cases the defrost should only last 20-25min then terminate via the defrost termination switch(X) terminal on the clock. The fact that you have a door that is not being closed with warm WIC air blowing into the WIF will also be an issue. Also check pipe chases and the box seams for air infiltration. You say the heaters only stay on a couple minutes? What's causing them to deenergize? A heater limit? The DFTS(sometimes they short internaly)? Are these switches located on the utubes or attached to a bracket? I have always set timers in WIF in restaurants to defrost every 6hrs and set the backup for 45min.

[Maven445]

The heaters energize after the second click, after the pump down. The unit is time initiated and temp terminated. That fact may resolve one of my concerns that the heaters do not stay on long enough. Once that coil reachs 50F the defrost termination switch will denergize the heaters and energize the solenoid. There are two heaters one loops through the coil and the other is a drain pan heater. Its a Heatcraft evap. The timer is set for 60 min every 6 hours. There are deffinetly more problems with this unit, I just wanted to understand how the timer works. If its set for 60 mins and the heaters heat up that coil to 50F within 20 mins will it cycle the heaters on and off or is the defrost over once the defrost termination switch closes?

[2sac]

Defrost termination switch/fan delay switch energizes the X terminal on the time clock which is connected to a soleniod that switches the NO to NC and the NC to NO and the freeze cycle begins again.
Edit: The heater safety and termination/fandelay are affixed to the side support located on the outlet side of the coil approx 1/2 way up from the bottom. This would explain why you continue to see ice on the top half of the coil if one or both the switches are bad. The drain pan heater may not be working causing the bottom half of the coil to stay frozen. Both heaters should draw the same #of amps. With the info given, I'd be wiiling to bet the warm air infiltrtion is the main issue which iswhy the front (outlet) of coil is freezing.

[jpsmith1cm]

Maven445,

You need to look at the system as a whole rather than focusing on JUST the timer.

The frost pattern you are describing is somewhat unusual and not likely caused by a timer problem.

Check your charge and superheat.

[2sac]

Maven445,

You need to look at the system as a whole rather than focusing on JUST the timer.

The frost pattern you are describing is somewhat unusual and not likely caused by a timer problem.

Check your charge and superheat.

Based on what the OP described

The front freezes up really bad with soft ice on top and solid ice on the bottom. The back freezes up just on top.

I also agree it's probably not a defrost issue.
Do you really think it's a SH or Charge issue? I understand your thought process to a point but the fact that the entire front of the coil freezing up makes ke think it's due to high humidity levels or air infiltration. It's been my experience that a charge or metering device issue would freeze the bottom or inlet portion of the coil, but shouldn't have an effect on the entire face of the coil. No? Could be a combination of issues.

OP, Have you checked fan rotation? Aftermarket Heatcraft fan blades have the hub on the opposite side as the OEM fans.(when installed the hub is on the motor side of the blade rather than the fan guard side of the blade) It's possibe someone could have replaced a fan blade and installed it backwards, reducing airflow across the coil.