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goedel · Jun 14, 2009, 09:17 AM

I have a central HVAC (gas furnace, split condenser/air-handler). It has a thermostat control. The air-handler's (A-H) fan motor is activated immediately for AC, delayed start and cut-off with heating.

About every two years, I find replacement of the A-H fan-motor relay necessary. I have never had to replace the relay on the compressor's motor. This time, the A-H relay remained "on" long after the thermostat had shut off the compressor. The relay is a small. Enclosed device. It is not awfully expensive, about $8.00 from a mail order supplier. It is a bother to replace, because of tight working conditions, bad spade-type connectors, etc.

Should it be necessary to replace this component as frequently as I find?

Perito · Jun 14, 2009, 10:15 AM

It definitely seems excessive. I expect that the designer selected a bad relay. Can you replace it with one that's rated to carry more current?

goedel · Jun 14, 2009, 12:36 PM

Thanks, Perito! I have thought of that but hesitated because there is not much space in the enclosure containing the relay.

The relay's box states "8FLA" and "18LRA". The solenoid coil is 24V.
What do FLA and LRA mean, please?

Perito · Jun 14, 2009, 01:50 PM

8FLA means "8 Full Load Amps". Full Load Amps is the amount of current that is drawn when a motor is running at its rated horsepower. Think of this as "running amps".

18 LRA means "18 Locked Rotor Amps." Locked Rotor Amps is the amount of current that is drawn when the motor is attempting to start. Think of this as "starting amps".

Space is always a consideration. Nevertheless, if you can find a relay rated at 25% more than the one you have, it'll probably last for many years.

goedel · Jun 16, 2009, 10:26 AM

Originally Posted by Perito

8FLA means "8 Full Load Amps". Full Load Amps is the amount of current that is drawn when a motor is running at its rated horsepower. Think of this as "running amps".

18 LRA means "18 Locked Rotor Amps." Locked Rotor Amps is the amount of current that is drawn when the motor is attempting to start. Think of this as "starting amps".

Space is always a consideration. Nevertheless, if you can find a relay rated at 25% more than the one you have, it'll probably last for many years.

Many thanks, again!

hvac1000 · Jun 16, 2009, 02:00 PM

Many if not all of those small relays are made in China now days. The quality is just not there anymore. As Perito mentioned a larger capacity relay would help the situation. There are other type relays available from RBM company etc that can be a higher rate and last longer. Some of these will require a bit of a rewire using wire nuts but you can locate the relay in a different location to make replacement easier.