Lac

[froezone]

I was sitting in class, and my teacher brought up the low ambient control valve. The way he explained it was it regulated pressure based on ambient temperature. Basically he said it has a temp. sensor on top that measure ambient temp. The device looks very similar to what I would call a headmaster. However I know headmasters work off of pressure diff not necessarily measuring outdoor temp.

Is there anyone familiar with this device. I cannot find anything on it. Sporlan (http://www.legacychillers.com/cms_data/uploads/Sporlan-90-30-floodedvalve.pdf) had this info, and it did have the lac info. However it says nothing about measuring the outdoor temp. to regulate pressure. I am a little confused, does such a device exist ?

[coolerinfrederick]

are you sure it wasn't a switch he was talking about

[tjc76]

The dome on top of the valve has an air charge which changes minimally with outdoor ambient. When the outdoor ambient falls, discharge pressure and receiver pressure also fall. When the system pressures fall, the pressure in the dome overcomes the condenser pressure, forcing the condenser port on the valve closed, which floods the condenser with refrigerant. At the same time, the discharge bypass port in the valve opens, which then pressurizes the receiver, keeping the receiver pressure at the valve's setting, usually 180 or 210 psi. The valve doesn't really sense ambient, it indirectly responds to ambient by way of lowered discharge pressure. An oroa valve maintains receiver pressure. An Lac 4 maintains discharge pressure. Lac 5 and larger maintain receiver pressure.

[VTP99]

LAC or Low Ambient Control
The Lac4 is a 3 way modulating valve that responds to discharge pressure & The Lac5 and Lac10 respond to receiver pressure. Headmaster is a brand name for ALCO. Ambient temperature dictates condenser pressure.

[froezone]

are you sure it wasn't a switch he was talking about

Yea, I am sure. We was using the sixth edition of Refrigeration and Air conditioning technology book. I had the fifth edition (my book had not come in the mail yet}. But my book came in the mail today. I checked it and sure enough there is such thing. It is a low ambient control valve. The dome is filled with refrigerant. On page 441 in the book it say's that according to ambient tempt the refrigerant in the dome will expand and contract and act on the internal diaphram. It says that if the outdoor temp drops below 70 degrees it will start regulating. Interesting I had never heard of it.

[prorefco]

I don't have that particular book, but by the way you described it, it sure sounds like the book mis-states how it works. I've been around this trade for a long long time, and have never seen one that senses ambient temp to control head pressure. But, there's been other things that surprised me to, so who knows??

[dangpgt97]

I had that book as well in school and remember thinking the same thing as you. The book doesn't accurately describe how the head master works and does lead you to believe it works based on gas in the dome responding to ambient. That is just not how it works and they all work the same. The head on a headmaster sits inside the condensing unit where the fan blows different temp air around. It would be very difficult to control a constant head pressure based on this so why would anyone do it. You were right to have questioned it. Good job and good luck!!