Old Lennox A/C not working

Old 08-03-17, 05:25 PM
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Old Lennox A/C not working

Our upstairs ac unit will not come on when I switch the thermostat on. Even if I turn it just to fan I get nothing. Checked all breakers etc and nothing is tripped.
Could the thermostat be bad. It is an old Lennox from early 90's.
Old 08-03-17, 08:53 PM
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As a service tech..... our first step is to check for 24vac at the thermostat and if not there then at the air handler connection point where the thermostat wires connect. We'd be looking for 24vac on the C and R terminals.

Some air handlers only have wires..... no screw terminals.

A typical problem is the wiring that goes outside to the condensor gets shorted and either blows a protection fuse or the transformer inside the air handler.

Turn power off before opening service panel.
If you're confused by what you see.... post some pictures. http://www.doityourself.com/forum/el...-pictures.html

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