mcquay roof top ac

[icecuber911]

Walked up on a mcquay unit that was calling for both cmpressors to run and only one was running. I had a wiring diagram for the control circut and used that to find the problem. This thing was off on low pressure. I hooked suction and this thing nearly pulled into a vac. Ok tracing out piping from condensor i saw some solenoids before txv. I can find no wiring diagram for the solenoids in the unit. I wish i had a model but forgot to get. This is your usual publix ac with heat reclaim and is a 500 series store. My question is why is there a solenoid downstrean in piping before txv? Whats the order of operation after the condensor in cool mode? I think if i know how this systems works after the condensor i might have a chance to figure it out. Thanks for the help....

[coastalref]

is the one solenoid off the discharge line and tee's into the distributor at the outlet of the txv? if it does it is for hot gas bypass capacity control, not sure what you are exactly asking?

[dirtyboy103us]

hey ice

depending on the unit it may have two solidnoid coils in there
one is for a main pump down for the ac, so when your calling for ac that valve should be energized, if not it pumps down and the low presure switch takes out the compressor's
should be an 20/80 25/80 fixed screwed into the head

the second is for what they call a smart coil for helping with dehumidity control or the second stage ac on the board if it gets to hot in the store they can by pass that coil for all the cooling they can get
these types have unloaders also run off a adjustable low presure control where the compressor contactors are located

this all depends on the age and model

[dirtyboy103us]

hey ice

depending on the unit it may have two solenoids coils in there
one is for a main pump down for the ac, so when your calling for ac that valve should be energized, if not it pumps down and the low pressure switch takes out the compressor's
should be an 20/80 25/80 fixed screwed into the head

the second is for what they call a smart coil for helping with dehumidity control or the second stage ac on the board if it gets to hot in the store they can by pass that coil for all the cooling they can get
these types have unloaders also run off a adjustable low pressure control where the compressor contactors are located

this all depends on the age and model

[tmciver]

This may have info you can use as well.
http://www.chillergroup.com

[icecuber911]

Originally posted by dirtyboy103us
hey ice

depending on the unit it may have two solenoids coils in there
one is for a main pump down for the ac, so when your calling for ac that valve should be energized, if not it pumps down and the low pressure switch takes out the compressor's
should be an 20/80 25/80 fixed screwed into the head

the second is for what they call a smart coil for helping with dehumidity control or the second stage ac on the board if it gets to hot in the store they can by pass that coil for all the cooling they can get
these types have unloaders also run off a adjustable low pressure control where the compressor contactors are located

this all depends on the age and model

I have to get back and look at this thing again. If i remember right i did see two coils. I guess with both stages calling the coil directly in the liquid line should be energized. Stage two is running fine. My only problem is with stage two. What energizes the pump down coil?