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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8769
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

What is your question?

Customer: replied 1 year ago.
i have a 10 ton carrier roof top unit with 2 compressors. I just inherted this job it looks like all safetys are jumped and the unit is not running. i replaced the stat but no avail. i have 24 v to the stat from r to y1 y2 and 24 v from r to g. When i jump out the fan or compressors the unit runs until i take the jumpers off. Also if i jump out up at the unit the same thing happens compressors come on and fans come on. Any thoughts?
Expert:  Rick replied 1 year ago.

I don't have access to Carrier specs. I'm going to open this backup to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

Expert:  Phil replied 1 year ago.


Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip icon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip icon, look for the '+attach files' link at left of your send button.

I can mark up the diagram with trouble shooting instructions.

Customer: replied 1 year ago.
Wiring diagram is not read able all faded. Like stated before everything on unit is bypassed. This is how it is wired. If I jump out at stat unit runs. If I jump out at terminal connection in side unit unit comes on. Thinking it could be a bad stat?
Expert:  Phil replied 1 year ago.

Thanks, ***** ***** compressor #1 runs when you jumper R to Y1, etc.. then the thermostat is defective, that is a correct diagnosis.

Thanks for letting me work with you. When we are finished, if my answer has been polite, professional,and thorough, please click one of the ratings . If you still need help let me know!. Expert is not paid for assisting you until you rate answer. Feel free to follow up for30 days at no additional cost.

Customer: replied 1 year ago.
Phil I will go.back to unit and try with another stat
Expert:  Phil replied 1 year ago.

Its easiest to just fit a jumper wire between R and Y1... at the thermostat, then remove it and do it again at the thermostat terminal strip in the unit... that will work best. It will tell you if there is a problem in the other controls or not, it may not be a thermostat problem... if the jumper does not work then you know there is a problem elsewhere in the control system.

If you try another stat, that might work, but you might also have it wired wrong, alsoi it will not tell you if the problem is elsewhere in the system.