DX units in winter

[y1a1n1k1s1]

IM new to this site, not HVAC experienced and expected to pick it up. I have 20-30 split DX units with R-22 refrigerant doing computer room year round cooling. I understand they have problems with the units in the winter. Is there anything I can do to prepare? What kinds of problems can I expect? I don't believe there are any crankcase heaters in any units, if that would help.

 

[KenRad]

Do you have the original documentation from the condensing units when they were installed? Based on how the units were equipped, they will have a minimum ambient temperature, below which they should not be operated. If they were not originally selected for low ambient, then shoot the design engineer. After that's taken care of, you will need to make some changes.

Crankcase heaters would be one. Head pressure control would also be essential. This is done with either condenser fan cycling, or a variable speed controller that slows the fan as head pressure drops. The safest bet would be to ask the manufacturer what you need to do to fit the units for the lowest ambient temperature that they will see.

---KenRad

 

[y1a1n1k1s1]

Thanks Kenrad. I should have added that the units range in size from 1.5 ton to 10 tons and that there are some units with variable speed controls on the condenser fans and some with wind guards around the comdensing units to block high winds in the winter. There is no original docs, 4 or 5 different manufacturers and many different styles. Oh well.

 

[absrbrtek]

What kind of ambients do you have during your winter? I have set up hundreds of units to run with variable speed fan cycle controls with no problems. They have run to -10F ambient. The only problem you normally run into is the unit tripping the low pressure control on startup. I usually put in a low pressure time delay bypass and add an adjustable low pressure switch set at around 5 PSI. I have yet to set one up that cant run trouble free.

Whos make units are these?
How many fans are you controlling on each unit?

 

[y1a1n1k1s1]

Thank you absrbrtek - I'm in the Boston area. I'll have to look into any low pressure controls. The problem is that I'm a sub to a sub contractor and the owner makes corporate decisions way up the food chain from me with little in put from anyone around here. I'm just expected to deal with the melt downs and my area isn't HVAC - a recipe for disaster Sounds like I'm being set up as a fall guy? Oh well.