HELP PLEASE!!

[martin&sonsa/c]

so i need to know what size unit this is i dont do alot of work on commercial roof top units this is a trane model#ysc120a4ela2w0. i first need to find this out and then i have another question. any help would be greatly appreciated.

[jayguy]

it is a 10 ton unit...asking 1 question at a time will take a long time to get your answers...i tend to get bored with threads that go on too long :)

it's not you...it's me.

[martin&sonsa/c]

ok so here is the problem t stst set to cool unit blower comes on but not either compressor or fan motor. contactors for compressors not engaging so i checked both transformers and they are good checked my low voltage at contactors and no low voltage. checked for low voltage at control board and i have low voltage. led indicator light is on continious no trouble code. iam wondering what possible causes and i realize it could be a number of things where am i losing low voltage to contactors.

[PortaChill]

First off since the blower is operating we can rule out a time clock or tripped smoke detector. You said you had LV at the board. What were your readings from?
R-C
R-Y1
R-Y2
Does this unit have an economizer that would be locking out your cooling?
If you are reading 24v between R-Y1&R-Y2 go back to your t-stat. If you are reading 0v between them then issue is within unit. Have you tried jumpers at the terminals? let us know...:whistle:

[dandyme]

does it have a conventional t-stat or a baysens?

if baysens, tear out the book and start at the baysens

[martin&sonsa/c]

t-stat is honeywell vision pro 8000. headed that way now quick question before i head that way if it is a lock out then by shutting power off to the unit at the disconnect for 30 seconds should reset the unit correct. and is it possible that iam losing my low voltage through pressure switch. thanks guys. man i love this work i really do. im obviously going to have to jump more into commercial work after this lol.

[hvac wiz 79]

I wouldn't shut it off right away. try n prove issue first. check the pressure switches if u think one may be issue ... if it has an economizer, like portacool said check there ... tranes r complex machines but with the right documents to assist u it helps BIG TIME .. I'm new to seeing trane on a regular basis & found when all the regular inputs seem normal but no power at contactor coils, checking out economizer is a place to start. . . jayguy again thanks for your assistance in giving me documents few weeks ago!