Headmaster

[Andy Schoen]

I got turned around in my thinking.

If you clip off the pig tail you will run at the "lower" setting.

So since you have R404A, leave the valve as is and it'll control to 180 psig.

Forgive me Andy.

You're forgiven.

[frigeguy]

[QUOTE=icemeister;1942941]Yes, you can use pressure controls for condenser fan cycling in combo with a flooding type head pressure control valve (or Headmaster) but you have to ensure the fan settings are above the operating range of the valve so they don't fight each other. Using ambient thermostats are preferred however because they cycle less and allow for better stability. Other options may include variable speed condenser fans and TD controllers.

Additionally, this method is usually limited to multiple fan condensers as it's recommended that at least one fan remain operational at all time...typically the one closest to the header end.

Pretty much all I work on is multiple fan condensors, lots of fun in the -10 - 20f range. The variable speed controlers work on the last set or last fan when there working. Most of them crap out, I won't mention any manufactures names, they also require transformers/ most of the stuff I work on is 3 phase. Over the years we have pulled most of them out and rewireing the first set with 3 phase motors, then setting a minimum 120 psig on the drop leg. This works on up to date stuff with ballanced port valves. On the Med temp were looking at a min of 60 psig across the TX valve. It should be the set closest to the inlet header end or you risk shocking the condensor at low ambiant (-10f) been there and repaired that way too many times with the variable speed set ups. I have yet to encounter any type of damper system, but most of the stuff I work on is 60 - 100 ton. SOME MANUFACTURES REQUIRE THE FIRST SET TO BE LOCKED ON OR YOU VOID WARRANTY. They are begining to come around to my way of thinking, as I show them drop leg graphs for jan, feb. The variable speed controlers usually last a winter, so i don't void warranty anyway. Just rip them out in the spring. Most of the problems occour because of heat reclaim, with condesor inlet temperatures around 68 to 75f if not colder.

You can stay within warranty, just keep adding drums, 400lbs usually does the trick. The customer pays and a full receiver in May is always a fun thing. Not the best solution.

Just to sum it up, hold back valve at 140 psig min / first set off at 120 psig min drop leg / ballanced port valves at all evaporators. This set up works at low load low ambiant conditions, with heat reclaim. This has also been tested on critical charge systems with no holdback, 120 psig drop leg is about as low as I have been able to go.