I do want supply & return temps before we go anywhere (yes the 150 reading is a problem)

For now…Forget what I said about buttons or anything else…(including the above)

I just want to know what each chiller flashes back & forth while it is running…

Thanks…

Steve~

Byron~

What you are seeing is not what you think…Those are not setpoints…They are the actual temps of the water leaving & returning after being heated by the air coils & that's what I wanted to know…You confused me when you described on & off temps  

Seems the one chiller does have a bad sensor (talk about that later)…But going by the other with 42 outlet & 50 return tells us we have a 8 degree loop TD (temp differential)

8 degree TD is a bit high…We are actually better off with a 5 or 6 degree loop TD.

High loop TD can mean lack of water flow, or air in the loop system…This is one of the "Most Important" things in a chiller system…Lack of flow or air, can cause frozen spots in the chillers plate coil & thus cause a rupture that would cause a loss of the refrigerant, and then fill the refrigerant system (and the compressor) with chiller loop water…Chillers are not cheap !!! and when this happens they are done….

I'm not saying this has happened, but you need to be aware of how important it is, and that it is something that needs to be monitored/checked often…Yes the chillers have protections for flow & freeze up but they are not always 100% effective.

• When was the last time the loop was filled ?
• Do you know where the loop pressure gauge, pressure regulator & fill valve are ?
• If so…What is the loop pressure ? (As I mentioned earlier should be 15 to 18 psi)
• Does the loop have automatic air bleeders ?
• If not…When was the last time it was bled ?
• Do you know where the bleeders are on each air handler ?

Back to setpoints:

The benefit of lower setpoints is better humidity removal & better overall cooling performance with the colder air coils… 

One of the reasons the loop TD is important is It can effect how low we can run the loop without risk of freeze up, or freeze up shutdowns…

The freeze up shutdown is set (fixed) at 38 degrees…So to avoid tripping that protection we must keep the outlet temp above that…

Also know that setpoint differential is fixed at 2 degrees and is sensed on the return water from the air coils…So with a setpoint of 50 the chiller shuts off at 50 & comes back on at 52 (return)

Now with a 8 degree Loop TD…That means we can only set a setpoint of 50, maybe 48 degrees to avoid shutdowns (I try to set for 40 degrees out) that leaves a degree or two of safety, but still allows us to run coil temps similar to a refrigerant system & take advantage of the better humidity removal & performance that goes along with it….But remember the 2 degrees fixed setpoint differential ?…This means the chiller/s won't come back on till 50 or 52 degrees…

Now if we can get the loop TD back down to at least 6 degrees…Meaning we can lower our setpoint to 46…The chiller will come back on at 48…That's 4 degrees lower than the above example, and when staging two chillers the secondary chiller could be set at either 47 or 48 thus the loop is never above 50…

To read your Cooling setpoint…Depress & Release the upper of the two buttons until the display reads CSP…It will then switch to display the actual setpoint for a few seconds…Then it will automatically revert back to the alternating loop temps.

Hope all that makes sense & BTW…DX systems (Direct Expansion or Refrigerant) are designed to run 36 to 42 degree evaporators (air coils)

Steve~

First thing I would do is go to the highest (elevation) air handler, find it's bleeder & with the make up water valve turned on, loop pump running & air handler calling for cooling (Valve open)…Open the bleeder & let it run for awhile…Either into it's own condensate drain pan or overboard if possible…

Then I would go back down to the chillers & check their bleeders to see if any foamy or milky water comes out…If so continue bleeding there till it runs clear…Then go back up top & check there again…Then go to each & every AH in between & check.

After that…Recheck your loop TD & see if it's lower than 8 degrees…If so, you have done a good thing for everything involved…Air in the loop will even cause premature loop pump impeller & housing failure from cavitation burns…Like a prop might get…

Steve~ 

Post edited 1:06 pm – January 16, 2012 by Steve Pooler

Ok Byron…If there is no air in the system…That 8 degree TD tells me you are maybe a bit shy on loop water flow…

Probably not a lot you can do about it easily at this point but it does tell me about the system…And if it were up around 10 degrees I''d be a bit more concerned…You may want to re-visit it come summer time & see if it is closer to 6 degrees then…

For now…I would set one chiller at 48 degrees & the other at 50…This should at max give a 52 degree return, and hopefully keep the out to the coils water around 40 to 42 degrees…(similar to a DX system at it's higher end)

If one chiller is enough to keep the loop below 52…The second will not come on…And if it does it will only run till the loop return is 50 degrees…

To change the CSP…Use the top button till the unit display's CSP & then temp…While the current CSP is displayed press the lower button…First touch (I forget which) either lowers CSP or raises it…Releasing the lower button & pressing again makes it go the other way…Once where you want it just leave it and the display will revert back to rotating in & out temps.

Try those above settings & see how it does..We can always widen them a degree if you feel #2 is cycling too much, or bring them down to 1 degree apart if you feel the loop is getting too warm…If you get a FRZ showing on a display, then we need to bump up a degree on both chillers…

Then go back in & tap the top button until it display's "dl"….this is time delay…The factory setting is 15 seconds, and both chillers are likely still set the same…I would raise one to start 20 seconds after the first…This might also help with breakers tripping…

Here is a PDF link to the DDC board manual in case you want to know what the rest of the settings do (Pg 7)

http://www.dometic.com/FileOrg…..81-DDC.pdf

We also need to get you a new temp sensor for the one reading 150…That chiller won't heat until we do…

If you still feel you need a new larger AH…I'm happy to help there too  

Steve~