Freezer Defrost - Fan On or Fan Off?

[David40]

Would appreciate some opinions.
Fan on or fan off, that is the question.

I do both Electrical and HVAC. On this particular job I am the electrician. I am wiring the controls on an old Hill ZER-5, 5 glass door, upright display freezer. It is set up for electric defrost. I have always understood that the fans should be off during the defrost cycle. The guy in charge of the refrigeration is making me wire it with the fans running continuously. He does not even want a fan control or defrost terminator on it. He tells me the coils will not defrost completely without the fans running, and of course I'm thinking the fans will move the warmth away from the coils.
Could someone with some experience with these please end my confusion?
Thanks

[mad fridgie]

Are your sure this is a freezer, frozen products inside, like ice cream and the like, 0F, -18C.
Then fan is OFF

[Grizzly]

There are some systems that use the Ambient air as the heat source to defrost.
These are usually for chill systems or those close to Freeze point.
I don't know what system you are describing, but it is not normal to run on the fans during defrost when using electric heaters.
Basically you want the heat source as "local" as possible.
The more heat spread around the more energy required to remove it once the defrost has finished.
Hence the way Mad fridgie has worded his question.
Grizzly

[lawrence1]

You can tell by the position of the heater rods,,,
1.If it is a finned type heater in front of the coil in the airflow it must be on for defrost,,,,
2.If it is under or in the centre of the evaporator coil and a solid type without fins then the fans must be off for defrost.

[multisync]

If you can see the evap then it will be fans off. If you can't then often the fans will run during defrost to clear the ducts. Open freezer well's always are fan on during defrost so a blanket 'OFF' for freezers is incorrect

Although I don't agree there should be no termination stat !

There should also be a fan delay stat to reduce the load on the compressor and stop moisture being blown around the cabinet as condensation ice droplets will form inside

[airmate]

Hi, on some old systems application with induced draft fan setup and defrost heater being mounted on airflow inlet side of evaporator coil, fans were made to run throughout defrost so hot air can pass through evaporator coil for defrost. I have seen them in some older type island freezers where fans do not turn off for defrost but had off cycle pump down and CPR for high back pressure protection after defrost termination.Defrost termination or overheat klixon must be wired for electric heater.But you maybe right, it may need fans to be turned off for defrost as all systems do these days.

[David40]

It's definitely a freezer but I'm not sure what's going to be in it. The place is a meat market so it could be used for frozen meat. Looks like I need to ask a few questions and take a closer look at the placement of the rods. Might even take a picture. I'll do that today and post the results this evening. Thanks

[lowcool]

are we in the 21st century yet,fans off mate.is the boss on medication and can i have the name of his chemist

[coolhibby1875]

if the heaters are only mounted to the front of the coil then fans should be on, if the heaters are mounted front and back or underneath the coil then they should go off, however there should always have some sort of termination on it weather you use fans on or off, as this could be a disaster in the making!

[David40]

Well, here is the story on this unit. They bought it used and it looks like it was hacked. Near as I can tell the previous owner did not have any form of defrost working. They probably did what we did when I was a kid; defrost it manually every few months.
The ZER-5 was designed to use hot gas or electric defrost. (Yes, I contacted Hill Phoenix who bought out Hill Refrigeration and they emailed me a copy of the original install manual.) Looks like this one was originally set up for hot gas, but someone added a heater rod. The coil is in the bottom at about a 40 degree angle and rod makes one loop across the top which is between the coil and the fans.
So, from what I have read here it looks like having the fans on would be the way to go since the rod is on top of the coil. Heat rises so the rod wouldn't do much of anything without some way of pushing the heat down through the coils. The manual says a fan stat should be used for electric heat so I'm going to try to talk the guy into using one.
I'll let you know how it works out.
Thanks for all the great replies.

[coolhibby1875]

it sounuds like its still hot gas defrost, that rod is there to defrost the air ducts, which means fans on during defrost, if this doesnt have hotgas anymore, that single rod wont defrost the evaporator 1 single bit, and you will be lucky if it doesn't ice up within a week.

[David40]

I finished wiring it all up the way they wanted it done, so if it ices up it will be an "I told you so." kind of a deal. If they don't have any leaks they might try to fire it up tomorrow. I'll let you know what happens.