Heating, Air Conditioning, Fridge, HVAC/Furnace Airflow issues


Hi, Jim.

Let me start by saying what my furnace and A/C are and then describe my issue.

I have both a Carrier Furnace and A/C. Furnace is a Carrier; Product Number: 58MCB100---11116 and Model # 58MCB100-16, A/C is model # 24ABA

I have a 2 story home built in 2007 with 2122 sq ft (Not including unfinished basement. It has 16 floor registers (8 on upper floor, 8 on lower floor) and 6 return air (3 on each floor)

Last summer I was investigating my common issue of having less air flow coming from my 2nd floor registers as most people do.

I opened my panel on my furnace and checked my furnace wires to see were the original HVAC installer had them installed.  

They had the Black "HI" hooked up to the A/C and the RED "MED LO" to the HEAT. I moved the Yellow "MED HI" to the HEAT.

I Turned the Furnace back on and it sparked and blew the fuse.

I checked and the Yellow and Black wire connectors and seen they touched a little.

I moved the wires to make sure the connectors didn't touch, put a new fuse in and turned the furnace back on. No problem.

Here's the problem. Every since the spark, I noticed an issue.

I have a Honeywell RTH7500D thermostat, and when I press the up arrow to turn the heat higher it blinks "COOL" and vise versa, if I call for A/C it blinks "HEAT".

The furnace will heat and cool normal TO A POINT. What I mean is, the blower speed seems to be reversed somehow.

I got out my Extech AN100 anemometer and checked the CFM coming out of all my registers in both the Heating and Cooling mode.

My unit has more CFM coming out in the heating mode, then the cooling mode?

I don't understand because it should have more in the cooling mode, since the Black wire (HI) is set to COOL and the Yellow wire (MED HI) is set to HEAT.

My upstairs avg out of the floor registers in heat mode is;  441.875 cfm and in cool mode; 409.15 cfm

My downstairs avg out of the floor registers in heat mode is;  574.575 cfm and in cool mode; 567.78 cfm

When I had the sparking incident, I guess it messed something up. The unit still heats and cools, but the thermostat saying cool when its heating and heat when its cooling is strange.

I am a novice when it comes to HVAC, I do not know much about it.

What could be the problem?

Any help would be great, Thank You.

All I can tell you is look at the wiring schematic pasted on the inside of the blower compartment cover/door.
Connect the blower motor wires as shown.
When the wires shorted it could have caused a problem in the thermostat or the blower relay portion of the furnace, maybe just wired wrong.

Heating, Air Conditioning, Fridge, HVAC

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Jim Barnhart


Fifty + years conditioning the air.


Answer questions about , residential and commercial. Answer questions about sheet metal fabrication. Fifty years plus experience. No answers for oil equipment, No answers for kitchen appliances, No answers for laundry appliances, I don't specialize in one particular area of the HVAC area, I'm more of a General Practitioner, Limited in refrigeration/

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