Flooded Evaporator Too Warm

[larryd]

We have an R507 flooded evaporator system that utilizes a Danfoss modulating suction valve to regulate the evaporator pressure/temperature. With the compressor running at 100% capacity we are seeing a 15 PSI pressure drop across the suction valve when the valve is wide open. Therefore when the evaporator pressure reaches 18 psig we have 3 psig at the compressor which results in a compressor low suction pressure kick-off.

In the past we were able to achieve evaporator pressures of 8 psig without the compressor kicking off on low suction. We want this lower evaporator pressure/temperature to increase our cooling. Could this problem be the result of an over or under charged system? We always see the receiver tank partially full of liquid but at times also see liquid accumulate in the condenser?

[SteinarN]

Either the valve is horribly undersized or the valve is not fully open. What type of valve and what type of pilot valve? How do you know the valve is fully open? Is there an adjusting screw to manually force the valve fully open?

[larryd]

Yes, we forced the valve fully open with the adjustment screw. We suspected that their were valve related issues several weeks ago and replaced the valve with the exact same model as before.

[SteinarN]

Did you replace the pilot valve also?

[US Iceman]

With a 15 psi pressure loss across the regulating valve it is either not open all of the way or too small as Mr. SteinarN mentioned. If the valve worked before and not now I suspect something is not allowing the valve to open properly.

[larryd]

Thanks for the input from both of you. We did replace the valve with the same model as before and replaced the pilot as well. We bypassed the pilot and forced the valve open with the adjustment screw.

I guess this is not a symptom that we would see with a correctly sized valve but an improperly charged system?

[roadienh3]

We have an R507 flooded evaporator system that utilizes a Danfoss modulating suction valve to regulate the evaporator pressure/temperature. With the compressor running at 100% capacity we are seeing a 15 PSI pressure drop across the suction valve when the valve is wide open. Therefore when the evaporator pressure reaches 18 psig we have 3 psig at the compressor which results in a compressor low suction pressure kick-off.

In the past we were able to achieve evaporator pressures of 8 psig without the compressor kicking off on low suction. We want this lower evaporator pressure/temperature to increase our cooling. Could this problem be the result of an over or under charged system? We always see the receiver tank partially full of liquid but at times also see liquid accumulate in the condenser?

larryd,

If you have measured 18 psig at the evaporator and 3 psig at the compressor, the 15 psig pressure drop you mention (far too much) is in the suction line. Perhaps there is a valve not open/ing all the way, or if the compressor has an inlet strainer, it may be partially plugged.

roadie

[US Iceman]

If a flooded evaporator is undercharged it may not have enough liquid to boil off to keep the suction pressure high enough, hence low suction pressure for undercharged.

If the evaporator was overcharged you would have liquid running back the suction line (possibly) although the suciton pressure would be high enough because there is a sufficient volume of liquid in the evaporator.

If the suction pressure is being recorded at 3 psig, where is this taken from (before or after the suction strainer, which is usually in the compressor or downstream from the suction service valve)?

By any chance does this system have a hot gas bypass (feeding hot gas into the flooded evaporator)? And, what are the compressor motor amps now (compared to before)? And, is the compressor fully loaded (you said 100%, but I'm just asking)?

[sterl]

The additional question added to US Iceman's is: Where is the Evap Pressure being taken? At the Regulator Access port or at the Evap itself or?

If these are honest pressures and the regulator did not eat up 15-PSID in its past, the Part Number for the old and new reg and pilot should be re- checked. Is there a Suction Accumulator, Suction Filter and so on in between the points of pressure reading?

How is the liquid level for the evaporator controlled? Has there been a drastic change in terms of the cooled fluid?

[larryd]

Sorry for the long delay, I have been on vacation. I suggested to the factory that the suction valve be replaced with a larger valve. The valve was replaced yesterday and they plan to test the system tomorrow or Wednesday. I will let you know if we see an improvement with the larger valve. Thanks again for your input.

[Gary]

Is this a multiple evaporator system?

[larryd]

This is a single evaporator system.

The good news is that the valve was replaced with a larger valve and much colder evaporator temperatures can now be achieved (-38 deg F). The Danfoss PM3-15 valve was replaced with a PM1-25.

Thanks for all of your inputs.