Dishwasher exhaust vent question
I know this is way off the HVAC supject, but it the exuasting question is still part of the whole theme of our industry. Was called out to a restaurant with a large Holbart dishwashing unit. The unit has it's own personal 12x12 stack that shoots up to the roof and there is attached the cutest little exhaust venter.
Employees complaining that after 12 years of perfect operation, the dishwasher is not exhausting the steam up and out. Jumped up on the roof and found the motor was on thermal shut-down. Noticed instantly that this poor motor (1/20hp 1550rpm 115v 1.1A) was not rated as a continuous duty motor, yet it is hardwired to the building to run 24/7?
I have not a clue how these big belt driven dishwashers that use high pressure steam and chemical dispersion, work. Curious though, that if they have their own venting system attached then what if this unit controls the exhaust fan attached up on the roof. Pulled the panel spent a few minutes going over schematics and noticed a dedicated relay that is wired to a set of terminals labeled "venter motor".
QUESTION I know that there is a very slim chance that anyone would know and I should be contacting the manufacture. But I want to see how involved I really want to get on this.
But has anyone seen/installed/touched/or come across one of these units and does the venter (per my assumption) should be controlled by the unit? Or being hardwired and running for 12 years non-stop, probably tripping out on thermal every 20minute, not an issue?
This really isn't my cup of tea, but I would really like to figure the motor issue out and get a foot in the door with this chain of local restaurants. They had the local techs come out and say that the venter was an HVAC issue and not their problem, "dishwasher is running great, sorry about the steam filling the kitchen! Heres my diagnostic bill, call a HVAC guy!"
Hobart dishwasher at Red Lobster store, Mod C-44A. Brings the vent motor on through a contactor in the dishmachine itself when a rack is pushed into the machine. Small reed switches (magnetic) tell the IC board to pull down contactors and set things in motion. The motor in the exhaust hood of this unit was 1/4 H.P. belt drive sitting vertically in the exhaust fan housing with adjustable pully. Of course need to amp out the motor when adjusting. I don't see any real problems dealing with it as long as your good with a wiring diagram. Should be under the top cover of the dishwasher itself. I have seen motor overlaod protectors get weak, but it sounds like an awfully small motor for the hood itself, amp it out, strap a probe on the motor encloser and take its temp.
Also check there make up air system to see that its bringing fresh air into the building, to much negative air pressure on the building produced by the exhaust hoods for the grills etc. could cause this little motor to work to hard. Loose belts on a MUA system have caused many a problem.
Last edited by ReferTroop; 04-07-2007 at 02:17 PM.
ReferTroop I really appreciate your reply. Coincidentally this is also a Red Lobster restaurant. And they are running that exact model Hobart system. My guess is that the original installers never installed this correctly. Like you, I am under the strong suspicion that the exhaust vent assembly is not correctly sized for the application. Being a direct shaft 1/20hp motor. I know this is not what should have been installed. I am leaning more towards what you experienced and that is installing a new 1/4hp belt driven venter and get it adjusted just right.
Next question if you ever stumble back into this thread?
On the main control board on top of the dishwasher. I obviously can see the terminals for the venter motor control. Attached is a the original warning label for the installers advising to utilize a 1.5A or less motor. Obviously a 1/4hp motor initial starting amperage would be a bit higher amperage than the manufacture would recommend. I know by adjusting the belt properly I may beable to get the load amperage down to a minimum. Just wondering if you happen to remember the model or manufacture of your venter unit?
The current one on the roof of this restaurant has no manfacture markings, a study of the Hobart site was'nt much help. I kind of wiped my hands of this dilemma when I realized that they need a electrician to come in and reroute the wiring from the main circuit board to the dishwasher control itself. Now I am wondering if I should actually replace the whole venter on the roof, too.
Need to get ahold of Hobart. Initial calls were not very helpful. The technician there I spoke with advised what you stated, but was not sure of much more than 1400cfm must be pulled up and out while the unit is running?!? 3.5 tons of air drawn through a 12x12 plenum through a damper all by a 1/20hp motor.......don't think so.
Please enlighten me on any other information you may have concerning your job with a Red Lobster Hobart system..... Thank you in advance
Last edited by slctech; 04-13-2007 at 12:06 AM.
We got a big a$$ Champion dish washer. Cranks out lots of steam. There's a giant mushroom fan on the roof running 24/7. Motor took a dump this winter and no one knew it. I was repairing a fire door magnet near the kitchen when all of a sudden the fire alarm went off and all the fire doors closed. I thought,"I couldn't have caused the alarm." Looked behind me through the door windows and here comes the steam. Went into the dishroom and you couldn't see the hand in front of your face. Those Yahoo's working the dish machine were still running it and still loading dishes like nothing was wrong. I had to yell at them 3 times to turn it off!
There's TREACHERY AFOOT!!!
Those large dish machine rooms are so noisy they probably did not hear an alarm. also they should be wearing ear plugs for the noise which makes hearing an alarm even harder.
There's TREACHERY AFOOT!!!
Right off hand I don't remember the manufacturer name, I will be there this coming Tuesday to do an oil / filter change on the walk-in-cooler and will go over to the exhaust and get you the specifics. (Mod#, H.P., V.A.C., etc...)
Originally Posted by slctech
Dealing with Hobart guys, (IMHO) is like a rocket scientist asking the local AutoZone counter person for a new cyrogenics tank. Ask the manager of the store for there facilities managers name and phone #, give him a call and ask for the original specifications on the blue prints for that store. Very possible it all started wrong in the begining, (have seen that happen).
I've always dealt with a very informed gentleman by the name of Dave Turner in the Florida main offices.
I will take my digi camera and post you some pics, I beleive the reason for 1.5 amp max is due the contactor in the dishwasher itself is a small potter-brumfeild. I would use those contacts as a control circuit for a 2 pole 20amp and route the supply voltage through the larger contactor, all of this could by mounted in the top of the dishwashers electrical panel and be accomplished without an electrician. Besides, us refrigerationists usually know as much or more about control / supply wiring than most electricians.
If you need quicker info or responses give me a call, Cell # 419-937-4913, office # 800-244-1863.....
Here is the site we use for concerns with Hobart equipment
but didn't find any wiring diagrams, thanks.
Originally Posted by Sparkplug101
I had to replace a dish roof exhaust fan in January because the chemicals they use eat the whole fan to the point the entire inside center of the fan collapsed into the duct.
When I removed the Heep of scrape metal I also found bx electrical wire run from the dish machine inside the duct which had very little metal jacket left because of the chemicals once again.
That was another fun day
Maybe the fan starts when the dish washer door is raised
The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.
Really appreciate all of your inputs. Especially appreciate you Refertroop!! I have a feeling that most Red Lobster restaurants are pretty much set-up with basically all the same equipment. I would'nt be surprised that the original installers during the new construction period FUBAR'd this pretty bad.
I was advised by the manager that a few months ago they had to replace all the vinyl walling in the kitchen for about $20k due to the inadequate venting of the steam and chemicals over the years. I really don't think this system has ever ran from conception as is should.
I am excited to see what specs you have on your Red Lobster unit, ReferTroop.
My scenario is a stainless steel vent hood that draws the steam from where the dishes are loaded and where they exit on the conveyor. It then runs straight up and out through a 14x14 damper to a 18x18 curb which my little venter sets on.
Thanks in advance.
P.S. MCR as for your experience with the amount of steam these things generate, I am told that when the venter is not working, the dish room literally fogs up just as thick with steam and chemicals that you can not see crap and its burning the poor workers eyes.
P.S.S. I have already shredded Hobarts technical site for troubleshooting guides and specifications without any success in establishing the proper venter size and suggested wiring methods or schematics.
Last edited by slctech; 04-16-2007 at 11:32 PM.
They were in a "fog" allright. They were pissed because they had to shut the machine down and had to do dishes by hand. The longer it took to do the dishes cut into their "hang" time
Originally Posted by slctech
There's TREACHERY AFOOT!!!