My carrier 48GS Gas Heating / Electric Cooling unit has an error code flashing "Limit Switch Fault" and states that the Indoor Fan Motor is not running, or to ensure that the supply-air temp rise is in accordance with the range on the nameplate. My dealer states that I do not have enough return air. I have had problems with the system not supplying enough air, period, hot or cold. But I do not believe that my return air is the problem. I have added one big 8" return line on top of what the dealer installed. I believe the Indoor Fan Motor is my problem. It is a three speed fan, & is wired for high speed. Any help???
The easest way to check to see if it is a return-air problem, is to remove the blower door and have some one depress and hold the blower safty switch (Remember this is only a test, do not leave the door off after you are done!) Then cycle on the heat and check with a thermometer the temp rise from the return air to the supply air. Check the name plate for MFG rating. Then try again with the door on. If the rise is greater with the door in place. The dealer was correct.