My heater blows cold air but sometimes it works when I play with the control knob

you have a problem with the heater/a/c controls there obviouly stuck on a/c you will need to strip out the control panel to see why the direction/vent , hot/cold , fan speed controls are not working , before doing this have you checked the fuses as there may be a seperate fuse for the control panel ,if this all checks out take to an a/c specialist as you dont want to mess around with a/c gasses etc

There are only 2 reasons for a problem like yours. Either the water is not going through the heater core or the ductwork under the dash has a problem. For checking the water flow, warm the truck up and then feel both water hoses connected to the heater core. They should both be hot if the water is flowing. If they are both as warm, then the problem is inside the cabin under the dash. If they are not equally warm, there is a problem with water flow.

Tip- For a time the manual heat control models(Not electronic) used a heater knob which could break on the backside of the knob. When it does this, the heater control shaft will not turn as the knob is just spinning in place. Gently pry the knob off and then twist the control shaft to see if it will now work.

not blowing air or when switch is on blows cold air when you have climate control knob turned over to heat? it could be a switch or blower motor or fuse if its not blowing any air. if its blows cold air when knob is on heat then is can be thermostat or low on coolant or it could be climate control module or it could be a air filter in dash.

bad heater control switch or resistor.

1. what year model is accord?
2. there are several doors in the air box
3. blend door (hot cold)
4. mode door (defrost, floor, vent)
5. recirculation door (outside air)
6. if the control mechanism is defective. the tech may have reached under the dash and manually opened the blend door.
7. which control knob does not work mode or temp?

check the sensor in the dash near the controls looks like a tiny vent see if it has dust build up

it sounds like the blend doors within the heater casing are broken and this is an expensive repair to be carried out at a reputable repair garage

You have a broken wire connection between the temperature control knob and the circuit board behind the center dash console. Vibration causes the failure and once the control knob gets loose the solder connection fails.

For someone that knows how to remove the dash unit and can re-solder a couple of new wires this fix should take no more than 1 hour. Make sure that you apply loctite to the heat control knob spindle nut when you re-assemble it.

The dealer quoted me 750 dollars to fix this issue and I found out that it's a common failure for this year. I fixed mine virtually for free but it took some tools and about an hour of my time.

Control panel going bad.

Replace the temp control on this car, it should be electrical control not cables.