Defrost Termination question

[zapatas23]

I was working on a walk in freezer today that had two bad condensor fan motors which I replaced...
I started up the unit and was waiting for the evap fans to kick on ( waited about 30 minutes )
Felt the evap. getting cold but the fans didn't kick on.
I jumped out the Defrost Termination control and the fans started... so i went and picked up a new defrost termination control>
When I got back the freezer was running @ 30 degrees> i put in the new control and started it up> same problem. fans did not start...

really weird senerio.. I need some opinions. would really be helpful. thx!

[2sac]

It's doing exactly what it's supposed to do. 30 minutes seems excessive. Sounds like you may have additional problems. I woud be checking the charge, and the metering device as well as compressor efficiency. Why were the motors bad? and did you clean the coil while you had them out?

[ammoniadog]

Was the coil frozen up from running without the fans? Did the compressor slug itself to death and bust its valves? What are your pressures and your evaporator superheat?

[slctech]

Probably the defrost termination and fan delay switch. As 2sac stated, it is either doing what it is suppose to be doing and not closing to energize fans until evap coil temp drops low enough, or it is faulty and sticking and not energizing the fans. Time to investigate just a bit more.

[jim147]

If the evap fans aren't running the DTT is the first thing I check. I had a tech order fan motors without checking to see how it got it's power and neutral.

jim

[zapatas23]

They had a power outage yesterday. Ive never seen two die at once tho. Charge is good.. little high head washed n blew out coil. Running at 285 n 32. Ill have to check out mire tmrw thx for the help

[2sac]

Betcha got a ZP charge on the powerhead. Should be good tomorrow.

[Tommy knocker]

Hot box and high ambient?
May take a bit to pull down enough to make fan Circut. Should pull down at a steady clip though. If coil temp is not dropping steady your problem is elsewhere, as pointed out earlier. Charge, TXV, headmaster, comp valves, etc.

[timjimbob]

Had a freezer that gave me fits.

Defrost heater was switched on the neutral leg. Intermittant grounded would bring the heater on with defrost stat open-sometimes. Usually after I left.

Acted the same way. Charge right, but slow pulldown.

Took forever to finally catch the defrost heater on while trying to cool.

[monkeyman#1]

I had a problem once, similar in nature, on a three door display freezer. Changed the fan delay switch and unit took off. Next day get a call, not working again. Arrive on site, it is working fine. Check charge, SH etc., all good. Put unit in defrost, comes out of defrost and all works fine. Hmmmm. Did that multiple times. Even emptied out the contents, let box warm up and tried it again, all good. Next day, same problem. Only this time when I arrive, fans aren't running. Start checking power and discovered no power to fan delay switch. Turns out that the wire that ran from the terminal strip, throught the box, and to the FD switch had a "break" in it somewhere, and would send power most times but occassionally would "break". Replaced that wire and all was good. Drove me nuts.

[Hugo castro]

Can a defrost termination mark ground and cause a short circuit?

[2sac]

Yes

[mrclean55]

If they can bum 4 or 5 hours they can work too.

[VTP99]

But that's Al Bundy surely he can't be a bum.

[ammoniadog]

Yeah, I know that guy. He works at a shoe store in the mall. His job is to help fat women stuff their feet into shoes all day.

At least he used to. Now I think he sells closets and has married a hot Puerto Rican chick.

[timebuilder]

Yeah, I know that guy. He works at a shoe store in the mall. His job is to help fat women stuff their feet into shoes all day.

At least he used to. Now I think he sells closets and has married a hot Puerto Rican chick.

And his daughter was the talk of the high school....

[MilfordsMrFixIt]

I ran into a KolPak unit recently that 5 different companies worked on. The symptom was similar, except that the coil was freezing up solid- randomly! The others had replaced the thermostat, the terminator/delay, the defrost limit, timer, contactor...You'd have thought that ONE of them would-a noticed that most of the heating element was not actually touching the coil! You know- there's a 'groove' in the coil that the element sits in and it transfers the heat to the coil?, Yah that!! LOL Simple enough to take a ¼" nut driver and tap it back in....jeeeeeez!
► As to the fans, you DID say that you changed the --condenser fan motors--, which have almost nothing to do with the --evaporator fans--. If the Evap fans do not start within 10 minutes of the defrost terminating, start by checking the (usually 3 wire) defrost thermostat. If it's below 35°f, the fans should run. If it's cold enough, Bypass it to test. Fans start= bad stat. Fans no= something else, possibly a problem with the fan delay in the defrost timer. (Most units rely only on the stat for this function)

[VTP99]

Fans no= something else, possibly a problem with the fan delay in the defrost timer. (Most units rely only on the stat for this function)

Where is this " fan delay in the defrost timer " you speak of ?

[MilfordsMrFixIt]

Well, there are a number of timers that control the fan delay. Usually formatted in 'time initiate and time terminate' mode. There is a terminal "F" for this purpose, however most clocks just use it to isolate the fan output to prevent feedback issues.
• This Grasselin control delays the "F" contact by a fixed 5 minutes. We found that out when the fans just would not come on. Of note, there are 5 relays on the board while most have just 2 or 3. Impatience on that one...LOL We rewired it to a standard DTFD as the fans were coming on just a little too soon causing fog in the freezer- alarming the users! One called the fire department reporting a 'Freon™ leak'! So we had to come up with a solution. (note the currently empty "F" terminal)
• The ICM 550 on the other hand just turns the fans on as soon as the defrost terminates. Note there are 3 relays, the small one signals the termination cycle.
• The electronic Paragon 9145 clock (love it) seems to be just a changeover as well. Great timer if you need to keep the times for defrost at exact times of day, or if you need to run short defrosts during the day, IE 15 minutes, and you can schedule a 90 minute at 4 am. The DTFD will still stop the defrost if it finished early.
◘There are a few models out there that delay the fans, few, but some.
▬ We have a customer that had a drive-in frozen warehouse that had 8 separate sets of condensing units and evaporators. that were all controlled by a single timer... and a boat load of relays and contactors! What a cluster---- that was. Initially I Converted them to individual timers. Imagine the inrush when 80 HP of condensing units all started at the same time!!! Their power demand went down enough for the accountant to notice!!
--As of now, I installed an Arduino Uno that's programmed to defrost one at a time for a max of 30 minutes, then hard delay the fans for 6 minutes and 30 seconds with a standard DTFD stat backing it up. So, at the top of each hour, a different unit defrosts, giving a defrost every 8 hours to each unit in succession. This keeps energy usage in line and also the temperatur regulation, which is controlled separately. It's been running with the Uno for 10 years now trouble free, there's a spare at the site pre-programmed if it's needed.

[BBeerme]

ICM using a Grasslin timer?

What is this world coming to?