Causes for rotted evaporator coils

[gesinc]

Hello Everyone,
I'm working on a Heatcraft, medium temp., walk-in. R-22. The condensing unit is: M/N MOH008D72CF S/N T03H01639. The evaporator is a BOHN M/N ADT070AK
S/N D03A11213 but has a Heatcraft label on it. The unit may be about six years old, but I've found several pin hole leaks in it. One in the tube sheet and three at the return bends. And one on a sloppy weld on the liquid line where it is connected to the evaporator.
Anyway, what would cause the pin hole leaks? And another thing, the fins are rotting away as well. What would cause that? It seems the best remedy is to replace the evaporator rather than chase pin hole leaks.
Thanks for the responses.

[engineerdave]

I've seen this too, mainly in Produce boxes. It's apparrently a result of moisture being pulled from the product. Fruits & vegetables are somewhat acidic....

Ya just gotta replace the coil unit when you start getting that rot & pinhole situation. Really no other way to deal with it, in my experience.

[jpsmith1cm]

What is stored in the box?

This sounds a heck of a lot like the deli type coolers that I work on. The acid content in the product condenses on the coils and mixes with the water and works on the metals.

Turns them into flaky crap in a few years.

[engineerdave]

I heard in the pub once that a guy had that situation, replaced the evap unit, but before putting it online he sprayed the fins & coils with varnish. Not sure how it worked out. Could be the story was BS, I don't know.

[Joe Harper]

A lot of restaurants cook the food and then rool it uncovered into the cooler. I have seen an evaporator eaten away in a year nad a half by grilled chicken.

[Joe Harper]

I heard in the pub once that a guy had that situation, replaced the evap unit, but before putting it online he sprayed the fins & coils with varnish. Not sure how it worked out. Could be the story was BS, I don't know.


Probably the same guy that sprayed the de-plated ice machine evap with food grade silicone to make it work :bump:

[absoair]

I've seen it on a few reach ins. The replacement coils had a coating on them.

There have been a few other threads on this in the past.

[dangpgt97]

Actually I seen the other day Nu calgon makes a product that can be sprayed on coils for protection in corrosive atmosphers. Never tried it just throwing that out there.

[crackertech]

What is stored in the box?

This sounds a heck of a lot like the deli type coolers that I work on. The acid content in the product condenses on the coils and mixes with the water and works on the metals.

Turns them into flaky crap in a few years.

X2 Bakery,deli,produce with deli being # 1

[Juleous]

You can buy evaps pre-coated or just buy a can of the blue spray. I have used it with good success, if I replace an evap coil in a kitchen then I always use the spray before I put it in. Just a little extra insurance, I have never had to replace an evap more than one time so it must work pretty decent. Some foods are worse than others for rotting out coils, lemons and limes are the worst I found, then fruit and veg, then meats. It really depends on the kitchen and the way they keep their coolers, some places I won't even work others you could eat the food that falls on the floor.

[gesinc]

Thanks for the responses. This one is in a kitchen in the county jail. So they store meats, vegies, cooked stuff, dairy products, eggs, etc.

Acids from the foods make alot of sense. So I guess it's not unusual for this coil to rot out in six years. Perhaps Heatcraft makes them with a coating. What's the name of the coating product?
I'll also be recommending service disconnects for the condensing units (freezer doesn't have one either) Plus a p-trap in the suction riser.

[jpsmith1cm]

Tell them to invest in air tight containers.

A lot of acidic foods are the most likely cause, but keeping them tightly sealed will do more to prevent the corrosion than any fancy coating will.

Either that or a routine PM program that involves a periodic cleaning or flushing of the coil.

[gesinc]

O.K. How often do you think the coils would need to be cleaned to prevent the acids from eating them?

[jpsmith1cm]

Maybe twice annually.

One good cleaning and a rinse down 6 months later.

I've never done this, so I am guessing. There would be a number of variables, but any proactive program HAS to help prolong the life of the coil.

Since the existing coil lasted 6 years with NO PM program, even an annual cleaning would help to prolong the life.

I doubt that it would totally prevent the acid action. As soon as the cleaning was done, the acid would start building up again immediately.

[gesinc]

Thanks very much for all the responses.

[H/P Man]

You can order a replacement ADT-070 with 'Bohn-Kote" to minimize corrosion in a high acidic application. see the last page of the link below.

http://www.thecoldstandard.com/res/pdf/BN-LOP-PL.pdf

[marter]

I work for wendys and we get all our reach-in evaps with the coating on it, oh and we also got a local metal shop to fab the enclosures from stainless steal, so they hold up really well

[absoair]

What effect does this coating have on heat transfer? I would assume it is minimal, but still curious.

[gesinc]

I'm putting together a quote to replace the evaporator. It will have the "Bohn-Kote" on it. Thanks for the link.

[thethomas4]

I've seen where someone has used a heavy coil cleaner an made a total mess of the Bohn Kote. Anytime I change a coil I get it and they last along time.

[icemeister]

What effect does this coating have on heat transfer? I would assume it is minimal, but still curious.

I've been told the loss is typically less than 5% for similar coatings.

But then, without any coating at all I would expect the loss of performance to be more than that in just the first year.

[mfry]

Manufactures using thinner copper to reduce costs is the main factor. When you do replace the evap. open up the tubing and see the thickness. Probably paper thin.

[Poodle Head Mikey]

A hot wings place and you can't keep evaps in it. In less than a year they look twenty years old.

If they store onions, especially cut onions - you can't keep coils in them. Even the coated ones down't hold up.

[kingvalve2]

Part of my job involves the maintenance of refrigeration equipment in a health care centre. This facility was built in 1979 and a lot of the equipment including the kitchen walk-ins are origional equipment. A few months ago I had a loss of cooling in one of the w/i coolers. This cooler is used mainly to store fruit, veggies, both raw and cooked. After 30 years, the evap finally suffered a couple of pin hole leaks on a couple of the u bends. Lol, they made things to last in the old days but these old evaps are finally feeling the effects of the acidic conditions caused by the products being stored in them.
A touch of sil fos, evacuation, a new f/d and recharge and we were good to go. These units are finally due for decommission within the next few months, good thing too, if not, I can see myself plugging holes every month or so.

I guess the lesson to be learnt here is that after 30 years of service any refrigeration system has paid its dues in full and owes nobody nothing.