Portable Chiller's

[ProFishional]

Anybody have any expericence with portable water cooled chillers? I got a s/call for a 5t chiller, Manf: Temptek, M/N# CF-5W.
Problem: not cooling. this unit is hooked up to process water lines to cool the head's in a stamping plant machine.
(process water temp 70 F.) unit is cutting out on h/p at 350 psi, low side at 58 psi, (evap tank/(coil) holding glycol temp at 46 F.
I checked this system found cond. water at the proper temp 70F,
the system seemed fully charged, holds 8.8 lbs R-22 w/ sight glass, which was clear.
Now I'm not sure who has been servicing this unit or if the unit is /was overcharged, but I removed 1 1/2 lbs of ***** from this unit which showed bubbles in the sight glass, but the unit is operating within its specified range: the glycol tank will cool to whatever setting you set it to from 32 F - 68 F. The head pressure stays in the area of 250-275 psi.
I'am I missing something by chance? I have never worked on one of these before.

Thanks
JT.

[Gary]

High head pressure is actually an inaccurate description of the problem. For starters, it is more to the point to report the saturated condensing temperature (aka SCT), found on our P/T chart, rather than high side pressure. You will find that troubleshooting is MUCH easier if you learn to think in terms of temperatures rather than pressures.

Then, unless the flow is controlled, we might expect lower SCT with lower water temp and higher SCT with higher water temp. So, first we would want to know if the entering water temp is excessive.

If it is not, then an accurate description of the problem would be: Excessive condenser TD, TD being the difference between the entering water temp and the SCT. By looking at the difference between these two temps, rather than one temp or the other temp, we take into account the affect that one has upon the other.

Excessive TD can have several causes:

First, let's look at the condenser approach temperature. This is the difference between SCT and leaving water temperature, and is an indicator of heat transfer efficiency between the refrigerant and the water. High approach means there is an insulative coating on the tubing between the refrigerant side and the water side. In other words, mineral (or other) buildup on the water side surfaces. Or (less likely) the piping may be set up for parallel flow rather than the more efficient crossflow or counterflow

Next we check the condenser delta-T (aka dT), this being the difference between the entering water temp and the leaving water temp. High condenser dT indicates insufficient water flow, this in turn caused by pump problems, misadjusted water regulating valve, dirty condenser, air trapping, etc. In short, anything which reduces the flow of water through the condenser.

Now that we have gone through the water side problems, let's look at the refrigerant side problems: Primarily, we need to look at the subcooling. This is the difference between the SCT and the liquid line temperature. High subcooling indicates excess refrigerant in the high side, backing liquid up into the condenser, reducing its capacity, or (less likely) non-condensibles.

There are other possible problems, involving relative component sizing and/or excessive loads, therefore it is best to have a full list of temperatures throughout the system, and Marc has provided a link giving you a list of relevant temperature measurements. I would strongly recommend that you provide all of that information for a full and accurate analysis.

For a bare minimum however, we need SCT (high side pressure converted to temp on a P/T chart), water in temp, water out temp, and liquid line temp.

[chemi-cool]

Hi ProFishional.

unit is cutting out on h/p at 350 psi

and then you write,

The head pressure stays in the area of 250-275 psi

that shows that you have to check the HP control.

Come back after you have checked it and let us know what did you find.

Chemi

[mrchatts]

I removed 1 1/2 lbs of ***** from this unit which showed bubbles in the sight glass,............................The head pressure stays in the area of 250-275 psi.
I'am I missing something by chance? I have never worked on one of these before.

Thanks
JT.

chem-cool.Think you missed above quote, this would lower head pressure

[shogun7]

If you would have followed Gary's instructions to begin with I don't think you would have needed to ask the question. I believe you did the right thing and the proof will be indicated in time. I would Keep Gary's instructions ...or buy his books

[Gary]

i.e. is it that the saturated condensing temperature is high or is that the condenser cooling medium temperature is high?

In my thinking system, a relatively low dT/TD ratio generally indicates restricted heat flux, particularly if accompanied by a low SC/TD (Sub cool/TD) ratio.

Then, a relatively high dT/TD ratio accompanied by a low SC/TD ratio generally indicates restricted condenser cooling medium flow.

That's an excellent point, Marc. In my post above, approach should be checked after subcooling. IOW, first excessive water in temp, then excessive dT (water flow problems), then excessive subcooling (flooded condenser), then approach temp (insulative coating).

Sequence is everything.