copeland demand cooling question

[tropicold]

Hello and a happy Christmas season to all !!
First the facts:
+ 5 year old equipment
+ Copeland 6D compressor
+ Demand Cooling, head fan, oil cooler
+ R-22, low temp, air cooled condenser
+ Multiple evaporators (5): independent suction and liquid lines, all routed to suction and liquid manifolds
+ Temperatures in freezers: three of them -12 deg C, one -7 deg C, the other one does not get below -5
+ Suction pressure: 1.2 bar
+ Condensing pressure: 13 bar
+ Main liquid line sight glass: clear
+ Suction line temperature at compressor: not above 18 deg, lot of condensation
+ Head temperature: not above 115 deg
Now the problem: demand cooling system operates almost continuously.
I learned that the liquid solenoid activates around 140 deg of head temperature, so I tried replacing the control module with a new one just in case it was out of calibration. No change.
Now the question: if there is no apparent reason for the overheating of the compressor, why is the DC operating most of the time ?
Best regards.

[Brian_UK]

Suction pressure of 1.2bar equates to -37°C
Suction pipe temperature of +18°C shows a high superheat.

This could be the cause of your overheating compressor.

[powell]

tropicold,

Here's a link to Copeland's AE bulletins.

http://www.hvacrinfo.com/ae_index.htm

Check out 4-1287 and 17-1260

Also, check your discharge line temperature 6" from the compressor. It should never be higher than 225 degrees F.

I bet it's high due to what Brian stated about the superheat.

[jpsmith1cm]

+ Head temperature: not above 115 deg


115 degees C = 239 degrees F. You are overheating in a BIG way.

Get the superheats down and your compressor will be happier.

[Magoo]

The demand cooling control is demanding desuperheating the discharge gas temp., not rocket science. OK , high suction superheat means high discharge temps and motor winding temps , the system is in cover ars mode. Suggest looking at over-all system conditions.
magoo

[coolhibby1875]

it sounds to me like the head gasket is burst or 1 of the discus valves is cracked and your passing discharge gas into the suction, However i would expect the suction presure to be a bit higher.

[coolhibby1875]

ps. you may have a bit air traped in the condenser i have had that on these systems it causes havoc.

[multisync]

Sounds like the valves are closing down or the drier is restricting (if after the s/g of course)

[Peter_1]

Important readings/facts we need to know
SH of each evaporator?
Aicooled condensor? Outside temperature?
Liquid temperature to TEV's?
TEV's anyhow fitted or EEV's?
Where exactly have you measured suction pressure? On the compressor , on the service vale or on the main suction manifold?
Is there a main suction dryer/strainer?
Do you have a dry indicating sightglass?

[smilies]

Demand Cooling module injecting=high discharge temps.

Do you ever have to reset it? Check the module wiring, some guys like jumpers across M and L.:eek: