[Mr. G]

Hi,

My AC unit stopped working. Everything just stopped. I went to the thrmostat and the heater won't start either. I took the fan out of the auto position and placed it to ON and it won't run. I checked for voltage at the door switch, it was there, external fuses and breakers were also good. I'm thinking I have a fan or control-board problem.

My system is under the house so I'd like some ideas before I start.

If I have an inop fan will it shutdown my entire system?

Thanks in advance.

 

[JJboy]

Start checking the 24v (R) at the thermostat. If you have 24v jump R - G. The blower motor should work.

 

[Mr. G]

No 24vac at thermostat or control board. I do have 110vac going into transformer and it appears I have output from transformer. I used an induction power indicator and it lit up on the black wire of the secondary.

I also tried the diagnostic test on the card which is suppose to run through the relays but nothing happened. It doesn't really smell and no visual indication of burns.

PN on the placard is 310305-201 rev. B

System is a Bryant 376CAV036055

The system is under the house so it lays flat.

Thanks.

 

[yuri]

Check if you have 24 volts between R and C on the board with the door switch pressed in. If yes and it won't run the self test then the board is bad. With the door switch open/power off check for continuity from C to ground/ground wire of the furnace. If not grounded it can damage the board or be the problem. Some of them give you an error code for that.

 

[Mr. G]

Since we've had perfect weather I've kind of let this project sit. Yesterday I took board out and tested the transformer. Bad primary coil, so no step down voltage. Hopefully that is it. Cheaper than a control board. Now to locate the step-down transformer.

 

[Marty S.]

Find the low voltage short before sticking the new transformer in.

 

[Mr. G]

What should I look for on the secondary side? I checked where the secondary is hooked up and it wasn't shorted. I'm thinking the secondary of the the transformer is used for control on the board. Thanks.

 

[JJboy]

Check continuity of the wires between control panel and thermostat.

 

[Marty S.]

Anything in the whole low voltage circuit could be shorted. Start at the AC and look for chafed wires rubbing on copper. From there you'll need to get the meter out and check each circuit. Put a 3 amp fuse in the secondary side

 

[Mr. G]

Found the two AC control wires stripped of insulation at the vent grill. Wires were stripped of insulation for about 3 inches! Probably animals, it was a cold winter here. I'll put in the 3A fuse on the secondary. I was watching a YouTube video that used a car fuse connected to insulated lugs. I'm hoping for no damage to the control board. Thanks for all the ideas and help.

 

[Mr. G]

Im starting to check everything now. I've got 18 ohms at the coil of the contractor. I noticed that the bottom of the cooling fins are corroded to the point of disintegration. About a 2 inch by 5 inch area. What can I do? Should I vacuum the rest of the fins? Any other PM I could do on the AC unit? Found a sheet metal place that sells a generic step down transformer for 12 dollars. I have to wait till Tuesday.

We only use the AC about 30 days a year so we've neglected maintenance, so any PM tips are appreciated.

Thanks to everyone for the help.

 

[Mr. G]

AC up and running! Thanks again.