I have a carrier heating unit installed in 2000... it worked fine since then but now... fan will work if we turn it ON by itself... but if we turn on auto heat then heater goes on (blower like sound) but fan doesn't force the air into the house... if we turn off the heat... fan comes on immediately...

It is gas fired central heating system... thanks for your help.

LED code comes out to 13...

The main limit is opening. You may have a bad control board. The board times the blower on in heat mode. If all your blower wires have good connection on the board I would say it's the board. You can have heat by turning the fan switch to on at the t-stat switch the mode switch to heat and set it the temp you want. The blower will run all the time but the heat will cycle as normal. And no its not bad for the blower to run all the time. It will give you heat until you get the board replaced.

Thanks... how can I replace the board?

The toughest part is paying for it. Usually they are under the cover where the filters are, follow the thermostat cable. Note, red on R, white on W,. Many of the other wires will be on one plug. Note any others and jumpers. Also the blower leads may be on one of a couple positions. If you don't note where wires were before removing them, then getting to back together and working right again is a mess. There is usually a few screws holding it in place.

The bad part is it's a rework kit. Its not hard to replace if you know some what of what you are doing. They send you a totally different control board with a lot of wires. Check with the dealer that installed the system, back then they offered the 10 years part and labor warranty with the unit. You may get lucky and its all under warranty.

I called my service guys.. they were nice and told me to reset a micro-switch... once I did it.. it worked like a charm. Thanks for your help T-Top.