If the limit switch opens multiple times during a single call for electric heat (fault code 3) the control will energize the blower until power is removed from the control.

The control will continue to cycle the heat outputs on and off as the limit re-closes and opens.

The constant fan operation will signal the homeowner that a problem has occurred and a service call is required.

The diagnostic light at the thermostat will NOT flash or provide any indication.

To reset: Line or Low Voltage Power to the air handler control board must be cycled.

Qty	Possible Causes:
	Dirty Air Filter
	Heat Fan Speed too Low
	High Duct Static
	Failing V/S Motor
	Bad Control Board
	Bad Limit(s)

Checkout:

1. Check Cabinet Insulation

Open the blower compartment and look for loose insulation that could block one or both sides of the blower.
- The most effective repair is to screw one or more metal straps the full length of the loose insulation.

2. Check for Water on Control Board

Especially in counter-flow applications, the control board is extremely susceptible to water damage from condensate overflow.
- If there is water in the base of the air handler, or if the control board has obvious signs of water damage ⇒ suspect a Bad Control Board

3. Check Limits & Board

Turn off power to the air handler.
- It is best to turn off power at the breaker box, as this test may bring you into contact with the inlet power wiring.
Disconnect the white molex plug from the air handler control board.
On the plug (not the board) check resistance between the Red and Brown wires.
- No Resistance Red to Brown = Open Limit
- Resistance Red to Brown = Limit circuit closed ⇒ Re-attach molex plug and re-power air handler.
  - Still Code 3 or 4 = Bad Control Board

4. Check Blower Operation

Activate a call for Fan by one of the following methods:
- At the thermostat, turn the "Fan" switch to "On".
- At the air handler control board, place a jumper wire between "R" and "G".
  - No Blower Operation = Bad Control Board or Bad Blower Motor

5. Check Air Filter

A dirty air filter will generally not cause a code 3 with a V/S air handler (but check it anyway).
With the filter in, run the unit in "Em Heat" and check the temperature rise.
Remove the air filter and recheck the temperature rise.
- Little or No Change = Filter Not the Cause
- Big Change = Clogged or Restrictive Air Filter