[cfe]

YORK D2CG120N20025JSB S#NFM13044---- MISSING #.

this is at Mcdonalds kitchen the lowest its get is 77*F. at 85* out door amb temp.
thermostat in the office with remote sensor in the kitchen. all exhaust fan work.
both stage reading the same Hi 245 Psi lo 65 psi compressor SH 18* R-22.
each compressor RLA 14 amp . name plate say 19.2 each stage.

cap tube with distributor metering devise.checked ducting in the attic all good.supply air 55* good air flow.
didn't check subcooling.
chemical pressured washed both coils. cleaned blower wheel.

per store manager work fine before until this summer. no renovation or anything changed to the store recently.

any idea? thanks

 

[cjpwalker]

Head pressure seems high for 85 degrees with clean coils. Are both condenser fans running (and are the running the same direction)?

Is your makeup air working in the kitchen? Is the economizer open?

What is the t-stat setpoint, and do they setback the cooling at night?

 

[hvac wiz 79]

Is your makeup air working in the kitchen? Is the economizer open?

These are my questions as well .. negative building pressure is a restaurants worst enemy and I find it more noticeable in the extreme weather. If the economizer is closed that would be potentially an issue. If the building was tested and balanced is this information marked in and on the equipment to set it back this way? Also make sure all air can flow with no restrictions like dirty grills and such


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[BaldLoonie]

Suction seems rather low for what should be upper 70s return air. How's the airflow?

 

[timebuilder]

One thing I have learned: unless I know from my own direct observation that all was previously well with a system, I cannot accept someone else's word that it was so. There are too many variables that affect the manager's perception of the system's operation.

I would also expect suction pressure to be higher.

Are there any fire dampers that are closed or partially closed?

 

[cfe]

this kitchen has no makeup air, economizer is at min position 20%.
t-stat is at 72* all time. store open 24hr. both condenser fan at right direction.
no fire damper. supply air flow good.
condenser fins are not in perfect shape but clean. lots of imperfect combed worked.

 

[firecontrol]

No makeup air? Meaning they're using the RTU's for the entire builiding as the makeup source? I'd make sure everything with the kitchen RTU was 100% and then find out what changed with the makeup situation.

I'm sensing this is the first time you've been on the site. If that is the case, nod when you're told everything was fine and nothing has changed and then go about proving to yourself that what you're finding with the entire building's HVAC is what you'd expect it to be. Always be suspect when they mention the word "recently". I ask for maintenance records when going to a new commercial job...... most times I get the deer in the headlights look, but sometimes they actually have things organized and written down.

 

[Mike19]

So they're using a 10 ton unit to provide makeup air, and cool the space?

So for heat loads right off the bat:
- Pulling extra hot air from outside in through economizer for makeup air
- Heat from hot side equipment in kitchen
- Heat from air-cooled refrigerators and/or freezers in kitchen
- Heat from people in kitchen

Its very well possible that its been 77* in there since that Sunline unit was new 15+ years ago.

How big of an area does this unit serve? Is it just the kitchen area or does it also heat/cool additional areas like storage areas?

Any big heat loads contributing to the problem, like a large air-cooled ice machine sitting there blowing hot air into the space as well?

 

[2sac]

You're removing all the conditioned air. Check the minimum position on all the economizers, or dampers and make sure they are not closed and fans are running constantly during business hours. An air balance is probably needed

 

[cfe]

You're removing all the conditioned air. Check the minimum position on all the economizers, or dampers and make sure they are not closed and fans are running constantly during business hours. An air balance is probably needed

i will look for that,
all refrigeration is water cooled, unit serve kitchen only,the kitchen around 1200 sqf.
closed some of vent that not need much cool air like kitchen hallway. wide open where cooking and preparation area where most heat coming from.

thanks for everyone input

 

[Mike19]

You could have duct issues too, its rare but insulation on the inside of ductwork can collapse and restrict airflow. Do you have anything you can check airflow with?

You could do a quick check by walking around and holding your hand up to all the registers to compare how much air is coming out. If there are airflow issues, that might help lead you in the right direction.

 

[alpharetta]

An air balance is probably needed

how air balancing can be done? is there specialist to do this?

 

[Aaronn]

There are air balance companies out there. Unless you wanna drop $5k on a flow hood. I would recommend keeping all dampers open, don't block off the hallway or this or that. Your just restricting airflow.

 

[michael013]

Only suggestion I did not see was..... Check the Heater and make sure it does not come on with the AC.......

 

[Aaronn]

Only suggestion I did not see was..... Check the Heater and make sure it does not come on with the AC.......

55* supply temp. 20-22 drop across the coil.

 

[michael013]

55* supply temp. 20-22 drop across the coil.

Yea saw that. Thanks for pointing it out...... Like no heater control has ever had an intermitted short and came on/off randomly.....gas or electric

 

[BALloyd]

Sounds like all of the McDonald's we service. Makeup air is pulled through RTU and duct work is garbage.

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[firecontrol]

You know how sometimes you have that one job that you want so badly to forget.... the one that you tell yourself to remember only the lesson(s) and let everything else go. Reading this post again brought back memories.

Ask the manager when the exhaust hood system(s) was/were last cleaned and serviced and if the conditions in the kitchen MIGHT have started soon afterwards.

Had an A&W restaurant that had the same issues you're describing. After giving everything the once over and not finding anything that stood out I went back into my ask lots of questions mode..... making sure to ask different people and in different ways. One of the kitchen help informs me that the exhaust hoods had been flagged by the fire inspector and a cleaning company had been brought in. They basically shut the place down for a day to remove the "mess" and get permission to reopen. The comment that brought the light bulb on was "after they were done it was a lot nicer working at the grills etc. because the hoods now pulled everything up and away a lot better."

Measured the air flow at the hood surfaces and found the air to be moving at about 500fpm.... if my memory serves me correctly. Again, memory tells me the design was 200fpm at the hood face.

I asked the manager if he had the invoice from the cleaning company. Seems the cleaning experts had determined that the buildup was due to lack of air flow and had "modified" the roof exhaust fans to "solve" the problem.

I had walked through the biggest "HELLO!!!!!!! There's a problem here!" indicator dozens of times......... the outside door to the kitchen and never put 2 and 2 together. If you stood in the open doorway it was like a wind tunnel as the outside air rushed into the building to relieve the vacuum created by the new and improved hood exhausts.

 

[pennwoods]

Check the economizers on the other roof top units to make sure they are open and the stats set for the fan to run all the time. Im surprized the kitchen economizer is only set to 20% considering its being used that way. The storw may be going negative when the stats satisfy causing lack of air flow at startup.

 

[joebear]

mcdonalds are notorious for small or restricted duct work,the stores I have serviced had 15 ton units in the kitchens