I have a Trane XR80 furnace and this afternoon it just started blowing cold air, so when I turn the heat up so it come on (when it kick on) all it does is blow cold air (no warmth at all).
The trouble code thing is blinking 4 blinks (light).
PLease help it is getting vary cold here in MN and I got a 3wk old baby!!

PLease any one know what it may be and how to check it or fix it?

From hvac1000:
https://www.askmehelpdesk.com/heating-air-conditioning/trouble-shooting-trane-xr80-furnace-279542.html Look on the inside of the blower door for the trouble codes.

I also found this:

2 flashes-System lock out
3 flashes-Pressure switch stuck open or closed
4 flashes-Open high temp. limit switch
5 flashes-Flame sensed without gas valve
6 flashes-115 volt polarity reversed
7 flashes-Gas valve circuit error
8 flashes-Low milivolt signal at flame sensing rod

https://www.askmehelpdesk.com/heating-air-conditioning/diagnostic-light-4-open-high-limit-device-278397.html

It's blinking 4 times.

From hvac1000, check:

https://www.askmehelpdesk.com/heating-air-conditioning/diagnostic-light-4-open-high-limit-device-278397.html

You can check the first three, the last two may require a service call