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I have a client with a system shutdown on high head pressure when trying to start his AC system at 130 DegF ambient at the condenser and the evaporator. If the pressure switch is jumpered out, the system will run and drop to normal operation pressures after 20-30 seconds. Any recommendations for...

My apologies for the vague reference on delta T. I was in fact looking for temp difference between inlet and outlet of the fluid. I will endeavour to be more precise with my future postings as it is quite clear that a thread can come unravelled if not properly mended. One could say "a stitch in...

In our case, the load (Q) is constant. We are only changing flow on a fixed system to determine a possible flow issue. We are seeing a higher than expected delta on the water side and wondered if there my be a flow restriction in the system (as indicated by the increased delta T). Thank you all...

We have a water/glycol brazed plate heat exchanger. In general terms, should we expect the delta T to increase with increased flow or decrease?

I understand the general requirement for sub-cooling. I guess what I am trying to ask is: Does the density of the refrigerant change as it sub-cooled? Is the density of liquid refrigerant at the saturation point less than the density of the liquid when it is sub-cooled?

Thank you for your candour MintJulep!! When the system compensates for the pressure loss in the discharge line, does that mean the compressor is working harder and so adds work heat to the system which is where the performance loss is derived?

MintJulep, To determine the required refrigerant charge for the system I assume a column of liquid in the liquid line. The liquid line would have a fixed volume. To calculate the weight of charge in the liquid line, do I use the sub-cooled temperature density or the saturated temperature density?

I am trying to determine the factors which contribute to the cooling loss rule of thumb. The high side is from the compressor outlet to the TXV. SCT is saturated condensing temperature and THR is Total Heat Rejection of the condenser which typically is the heat removed by the evaporator and the...

When working out the sub-cooled liquid density, do you use the sub-cooled temperature or the saturated pressure liquid density. For example: R134a at 300psig has SCT of 160ºF and liquid density of 61.74 lb./ft^3. However, it is sub-cooled 10ºF. Do I then look up the liquid density at 150º which...

I have heard of a general rule of thumb for R134a refrigerant that 1ºF of cooling is lost for 2psig pressure drop on high side. If the pressure drops on the discharge side, the SCT decreases and thus the we would be closer to the SCT for the discharge pressure. Is this not an advantage to...

Compositepro, That was my thought also. Once the cold refrigerant gas mixes with the hot compressor crankcase, any refrigerant absorbed in the oil will boil off.

VPL, If there was air in the system, our pressure/temperature ralationship would typically show unusual readings and we are seeing "expected" discharge and suction pressures for the ambient conditions.

David, Thank you for the response.... The compressor in question is a Bitzer F400 reciprocating "transit" compressor. The oil sight glass is located in the compressor sump and is for cylinder lubrication. The Bitzer compressor is used to replace two (2) TM-21 swash plate automotive compressors...

What is the result of excessive pressure drop in the suction line? I typically have seen suction line design for 1-2 psig drop. We have a bus AC system measuring 25-35 psig drop from evap out to compressor suction. The line sizes are obviously too small and that is being changed. However, I...

imok2, Your post caused me to review the specification ASTM B31.5 and I realized the annealed value has to be used with Type K and L but not with ACR tubing. Thank you.

We are looking at designing chiller packages using R410a refrigerant. The problem I have is selecting the tube size for R410a pressures. Using the ASME B31.5-2006 only allows me to go up to 7/8" copper lines with R410a working pressures (Type K, annealed copper). Is there another type of copper...