HVAC - both blower and fan will not start, contactor not pulling in.

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DeltaDave

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I have a package unit on my roof. It stopped running. I have checked all the electrical. 120 (x2) out of 30 amp breaker. 120 (x2) power to disconnect and out of disconnect and slow fuses are good per DMM. 120 power on line, both legs of contactor. Disconnected and bypassed thermostat at board. Nothing. Contactor is new and checks fine with DMM. 120 power through each leg of contactor (load) when depressed. Pushing in contactor does not start unit. 120 to circuit board. 120 to capacitor. 120 to 24v transformer. NO 24v on transformer or coming out of circuit board. There are no manual reset switches and no door switch. There is no status light or fuse on the board. Neither condenser fan or blower will start. Suggestions on what I can check next? Thanks in advance!!
 

WorthFlorida

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It's the 24 volt transformer. Every A/C tech will have one on their truck. They're quite cheap but do fail regularly. I had one go bad and not soon after my failure my friends 24volt transformer also went bad. The 24 volts runs all relays, circuit boards and thermostats. Some boards may have a voltage regulator for 5 volts for the electronics. However, many digital thermostats only use the installed batteries, therefore when the 24 volts goes away the thermostat may still look like it's working but the 24 voltage is switched through the thermostat to bring power to the relays for the compressor and condenser fan and the evaporator fan motors.
 
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Jason Dupont

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First of all check the capacitor whether it is working or not. If the capacitor is having problem then replace it else get your system checked by a professional.
 

DonL

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Yes, but 24v not coming out of transformer?

You need to find out why 24VAC is missing.

A bad cap will not cause your problem. You need 24 volts or you get nothing.

A cover safety switch may disable the 24 volts too.

Good Luck.
 
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