Carrier Chiller loses water pump pressure when compressor starts ?

[dman66]

Alright guys, I'm hoping that someone here can help out. I have a Carrier 30HL030 , 20 ton chiller which has an air cooled condenser, and chilled water evaporator. My problem is that the chilled water pump runs fine by itself @ 30lbs discharge and 12 lbs suction. As soon as the compressor starts on the chiller, the chilled water loop pressure drops in seconds as to where the pump suction will stay in a vacuum and the discharge goes to 18 lbs. At this point, I have to add a little water feed to the suction, just to get the loop pressure back up. I have not found any expansion tank. The building return water goes through the barrel first then goes to the pump suction. This only happens when the compressor turns on. Compressor operating pressures are @ 68lbs suction and 245 lbs discharge unloaded. I'll have my tech double check unload amps and load amps tomorrow.

[dman66]

Condenser is on the roof top, chiller in the basement three story building, liquid line sight glass is full on start up right before TXV. I first thought of a water freeze up, in the barrel, but not within seconds of start up.

[Unloaded]

Just a suggestion, I would start by verifying that you have the correct water pressure for the system then make sure there that any air in the system is vented. Measure the pressure drop across the cooler and refer to the flow requirements in the installation and startup manual. What type of cooler is it ? Shell and tube or Brazzed plate? Ive seen the brazed plate coolers freeze up real quick

[nyrb]

How far does the water piping rise above the pump, just asking because 12 psi will only keep the system full of water to a height of 27 feet, You might want to increase your system pressure a little to see if the cavitation stops. The lack of a cushion tank could also be an issue on the system.

[jimp]

Brazed plates freeze fast, especially if its dirty.

[dman66]

My tech was drawing blanks today - pulled him out. The building is only 30 feet tall rise. I believe that possibly, that the heating and cooling system may share the same expansion tank. This system is not a brazed plate heat x , but a hot deck / cold deck system. Seems like I'll never make a transition into the office.

[bbarry464]

If pressures are fine until you turn on the chiller, this would indicate temperature is the cause of pressure loss. Investigate expansion/bladder tank operations.

[jman2794]

Maybe if the tech on the job is provided this site to use and wants to you can get to office. Why are you trying to be the mediator? Maybe ego. You've established he's your tech already let him have some ownership of this issue

[Bklyntek]

If the pump is drawing through the barrel first,it becomes an extremely expensive water strainer. Compounded by signs of expansion and contraction. You need to open and check both water inlet and outlet of the barrel,you may find your problem.

[Tech83]

Check pre screen on the pump and also would boost pressure on the system. Think the calc I was taught was 1.25 per foot of rise for pressure set point. Usually worked for TAB guys if proper pump was installed. (Actually had guys install wrong pumps between 2 schools 7 1/2 for a 5... what a mess that was. At least 1 school was cooling)

[dman66]

As of now, we never had a chance to go back to find the issue. The owners of the building shut down the system when they were moving out of the building. Then they wanted us to come in and get the system back up and running a couple of weeks after they had moved out. They were showing the building to potential buyers and wanted the system running. That is when the issue started. I had to pull my tech because he told me he was at a dead point of not knowing what the issue was - an honest guy right there. I wanted him to fire up both the heating and cooling system as this is how the system ran fine before - he never tried it. The customer asked us to just let it go, and they would sell the building as is. I'm sure we will have another look at this once the building takes on new owners. If that occurs, I will post back what actually was the issue. The owners moved out and bought a school to move into, with nice newer Carrier equipment that the schools maintenance staff had really neglected all the equipment - here we go again, but happy to have the work.

[Nuclrchiller]

When they moved out and shut down the system, did they have the water service shut off? That's where the make-up for chilled water comes from.

[jimp]

The eternal mystery.

[dman66]

No the building water was not shut off. Jeezzzz. If we go back, and get a chance to look into this, I will post back. I strongly feel that there is an expansion tank issue for the cooling system.

[jman2794]

How far does the water piping rise above the pump, just asking because 12 psi will only keep the system full of water to a height of 27 feet, You might want to increase your system pressure a little to see if the cavitation stops. The lack of a cushion tank could also be an issue on the system.

Can you elaborate some on this Nyrb? I'm guessing it has something to do with the weight of water per vertical foot. I thought you needed a pump curve. Looks like thread is has come.to a halt but I noticed this valuable question you presented and info would.help.me.