Carrier 48SB-030080301 1990 model nat gas. On a/c mode works fine. Heat- burner lites but blower will not come on at all unless on manual. I changed the J2 jumper on thermostat from hg to he to see if I could get by for a while and its been working for about a month now. Other than blast of cool air at first we are staying warm. I've read previous questions answered on this subject and I think I have a bad relay. If that sounds correct can somebody tell me where to find the relay on unit. Also could it be anything else. I don't think I have one of those high dollar circuit boards on this unit. Thanks

If it has one, check the thermocouple.

I just had to replace one not long ago.

One end of it will be next to the pilot light flame if you have one.

Good Luck!

The relay is made into the control board. The blower is brought on by time(logic in the board). Cooling is high speed blower, heat is low speed blower and if you turn just the blower on from the thermostat it uses the same speed as heat (low). I hate to say it but it sound like you have a bad control board.