Hi *,
After a power surge in FL AC (Trane xe80 heat with gas/cool elec.) wouldn't start. I changed a couple of circuit breakers that tripped, one outside to the AC unit outside, one inside to the furnace. Power company came over and checked power in the outside unit. It has power and can kick-off using the switch. Inside unit shows a blinking red light (one per sec) in the control board White-Rodgers 50A50A-471. Thermostat Hunter 44100.
I thought it might have blown the transformer. I checked the transformer and there is power coming out (27V, enough for 24V), but no power going to the thermostat. So I figure may be a fuse somewhere else? but where are the fuses (if any)? Inside the control board? I unscrewed the control board, do I need to take the electronic circuit component out to check for fuse(s). I didn't want to pull it apart.
Help please, this is Florida and it is August.
Thanks.
Inaki.

A lot of furnaces have a plug-in automotive type fuse normally 3 amp in the circute board and are kind of hard to fond with all the wiring running around and across the board, look close

Well I took the circuit board and no fuse was found there.

Hello hvac1000,

Sorry to bother. I have posted a question this morning and followed some of the recommendations you had made previously to other owners of a trane xe80. May be you could help me out. I'm pretty sure that my problem resides in the 24V circuit coming out of the control board (White-Rodgers 50A50-471). For some reason there is no power going to the thermostat although there is 24V after the transformer (27V I measured). I opened the control board, but couldn't find any fuses there. I checked the drain pan switch and jumped the two wires and nothing...
How could I rule out the thermostat? Could the thermostat have blown due to the power surge? I can read the info, temperature is correct and it 'clicks' internally when I set it to cool/heat with the relevant temperature.
Thanks in advance for your time.
Inaki.

NOTE jump the thermostat out of the circuit.

Note your modual is nla but this one is close I think.If you have the open style board let me know.

http://www.white-rodgers.com/wrdhom/.../0037-6265.pdf

Trouble chart
http://www.white-rodgers.com/wrdhom/...pg0259_264.pdf


Thermostat

http://noblewinds.info/Hunter/ThermIns/44100.pdf

Jump the red to the green and the blower should come on.

Jump red to yellow and the compressor should work. NOTE!! There is a built in 4 minute time delay for the a/c to kick on at the thermostat so you will have to wait a few minutes to see if it works. NOTE hit reset as shown. See figure 5 on the thermostat paper I posted.

Now if you jumper at the board there should be NO time delay.

Please post here if any more questions.

Hello and thank you for your answer.
I jumped red (from transformer) to yellow (both at the control board and thermostat) and red (from transformer) to green (both a the board and thermostat) and nothing happened. I can read 24 V at the Control board when I jump, either yellow or green. What does this mean, is it the board or the thermostat?
Thanks again for any help.

Looks like the board from this end. If you have 24 volts at the board and it is not activating the relay for the blower with the use of jumpers the board has to be defective.

Power surges can damage more that on item. So after you replace the board check the system for proper operation in heat and cool.

BTW there should be a fuse on that board.

I'm including a of pic of the Control Board. I don't see any fuses, at least the car type.

This might be a closer board than the one I posted before.
Since I cannot find your exact board it is the best I can do.

Note the flash or solid indicator meaning. To lunch be back in a few.

http://www.white-rodgers.com/wrdhom/.../0037-6266.pdf

Ok, so I got a new 50A55-843 control board. I installed it cable for cable. Actually it matches pretty well my previous board (see picture above - 50A50A-471 jpeg).
I restarted the system with thermostat to 'off' position. The blower for both heat and cold started in the inside unit. After 5 seconds the heat fan stops, but the blower keeps running on and on. There is a 5 blinking code on the board that according to the installation manual means 'Open rollout switch'. As far as I know I can't seem to find any open switch. Any ideas what this could be or be caused by?

The outside unit does not kick-off and the thermostat controls don't seem to have any 'control' over the board or the blower because it keeps running in every position (heat, cool and off). Thermostat is Hunter 44100.
Any ideas or suggestions would be appreciated.

Also, what is the 'recommended' sequence for starting the whole system? I have power breakered off both the outside unit and the furnace. Then back 'on' the outside first and then the inside unit. Should I try the other way around or does it not make any difference?

Thanks again.

Inaki.

There usually a roll out switch in this model. Look on the inside unit wiring diagram on the inside of the blower door to locate.

The thermostat could have also been fried by the power surge/power outage.
Take the yellow wire off the thermostat when the unit is running and the outside unit should not run. If the thermostat will not turn it off and pulling the wire does it is probably the thermostat.

Also, what is the 'recommended' sequence for starting the whole system? I have power breaker off both the outside unit and the furnace. Then back 'on' the outside first and then the inside unit. Should I try the other way around or does it not make any difference?

It really makes no difference but for testing I would start the inside. Then check to make sure the thermostat controls the blower for on and automatic. Then continue with the rest of the tests.

I would still find that # 5 fault roll out switch and replace it before continuing.

Sometimes is a good idea reading the complete installation manual. I work in IT and I should know this by now... I've sent too many RTFM in my career I must admit.
There was a small blurb in the instructions that said I had to jumper the R01 and R02 wires in the 12 pin connector for TRANE applications like it is the case with mine (xe80). The jumper cable is provided by White Rodgers. And it did the work first time. Heat/Cold & fan all worked again! I was surprised to see the thermostat works fine. I thought it was fried too.
Anyway, BIG thanks to everybody that has helped with this in this site. I'm truly in debt with you. I'm sending you good vibes from warm and rainy FL. Best.
Inaki.

Glad you got it going.