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Old 08-17-2011, 07:34 PM   #1
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Heat/AC/Blower Won't Start


Hey Everyone,

About a week ago my central A/C stopped working. No outside fan movement, no inside blower movement. I tried switching to heat mode and again, no heating element, no blower. I tried putting the thermostat in manual on mode, still nothing.

The furnace is a Comfortmaker RPJ II. Model: GUI100A016BIN.

I've tried the basics. Pulled the filter. Checked the drain line. Checked the circuit breaker at the house and outside at the A/C. I don't see a reset switch anywhere. The furnace power cutoff is in the on position (for tests, off when making changes obviously). Same with the door cutoff switch.

I've tested the blower by jumping the cool line to the door cutoff switch. The blower starts up fine.

I've test the thermostat. In cool mode, I'm getting continuity on R & Y (blue in my case) as well as R & G. In heat mode, R & Y get no continuity, but R & W do.

I decided to replace the control board from the White Rogers model 50A50-110 to the supposed replacement part 50A55-843...but the problem persists. I get no LED warning lights.

I'm all out of options here. Any suggestions?

I bought a multimeter for this issue. First time using one, but I'm fairly certain I'm doing it correctly. The continuity test is audible, so seems hard to screw that one up.

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Old 08-17-2011, 07:59 PM   #2
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Heat/AC/Blower Won't Start


Do you have 24vac at secondary of transformer?

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Old 08-17-2011, 08:22 PM   #3
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Heat/AC/Blower Won't Start


You will need to check the transformer voltage. Before you do that, look on the transformer for a reset button, or for a fuse in the low voltage wiring. If the fuse and/or reset are ok, its time to check the voltage out of the transformer. To do this you will have to have the cover off of the furnace, and the door switch taped closed. This is time when you need to use due caution, as you will have your hands around live wires.
On the control board there should be 2 terminals marked 24 volts, one will have a "+" and the other a "-".
You need to have 24 to 28 volts at these terminals. One probe on each terminal to check this. If you dont have the voltage at the terminals, then you need to check for 120 volts going in to the transformer. Since you jumped the fan out im going to assume that you wont kill yourself doing this..
If you have 120 into the transformer then its time for a new transformer. You will also need a fuse holder to wire into the low voltage side of the transformer. You can also use two insulated female spade connectors, and 3 amp automotive fuses.
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Old 08-17-2011, 10:09 PM   #4
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Heat/AC/Blower Won't Start


Quote:
Originally Posted by Master of Cold View Post
You will need to check the transformer voltage. Before you do that, look on the transformer for a reset button, or for a fuse in the low voltage wiring. If the fuse and/or reset are ok, its time to check the voltage out of the transformer. To do this you will have to have the cover off of the furnace, and the door switch taped closed. This is time when you need to use due caution, as you will have your hands around live wires.
On the control board there should be 2 terminals marked 24 volts, one will have a "+" and the other a "-".
You need to have 24 to 28 volts at these terminals. One probe on each terminal to check this. If you dont have the voltage at the terminals, then you need to check for 120 volts going in to the transformer. Since you jumped the fan out im going to assume that you wont kill yourself doing this..
If you have 120 into the transformer then its time for a new transformer. You will also need a fuse holder to wire into the low voltage side of the transformer. You can also use two insulated female spade connectors, and 3 amp automotive fuses.
120 in, nothing out. Looks like we have a winner.

There were actually two transformers down there. One wasn't hooked up to anything, so I'm assuming the job has been done before. I'll head down the block and pick up a new one tomorrow and report back. Thanks!
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Old 08-18-2011, 02:03 PM   #5
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Heat/AC/Blower Won't Start


If not, a new capacitor may be in order. If you haven't put in the new transformer, try to move the fan blades with a wooden stick or something (not your finger!) when the unit is calling for cooling. If it spins, likely capacitor is bad.
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Old 08-18-2011, 06:34 PM   #6
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Heat/AC/Blower Won't Start


Just got the new transformer installed and everything is back to normal. Thanks a ton for the help!

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