Carrier Gas Furnaces: 58ZAV
Re: Flashing Code 33 / Fault Code 33
Flash Sequence = 3 Short Flashes + 3 Long Flashes (- - - , — — —)
Code 33 = Open Limit or Roll-Out
On Carrier 58 Series Furnaces, the Primary Limit is wired in series with other limits, including up to two Roll-out Switches or a Fusible-Link roll-out switch.
Therefore, a Fault Code 33 can be caused by one of the following:
- Primary Limit Switch Open.
- Rollout Switch Open
► If the limit circuit stays open for more than 3 minutes, the code changes to Code 13.
Qty |
Possible Causes: |
|
Dirty Filter |
|
Clogged Evaporator Coil |
|
Restricted Ductwork |
|
Bad Heat Exchanger |
|
Bad Limit Switch |
|
Excessive Gas Pressure |
1 |
Bad Control Board |
CHECKOUT:
1. Check Furnace Operation
- Start the furnace with a call for heat.
- If there is power on "W" at start-up, the furnace will run the blower for 90 seconds and flash a Code 12.
- Code 33 Immediately or Before Burners → Step 6. Check Limit Circuit
- Blower motor should start within 30 - 60 seconds after ignition.
2. Check Blower Motor
- Restart an ignition sequence and allow burners to ignite.
- Check for 115VAC between "Neutral" and "Heat" on the control board.
- No Power = Bad Control Board
- Power + No Blower = Bad Motor or Capacitor
3. Check Temperature Rise
- Check the temperature rise as the furnace operates.
- Compare the actual temperature rise to the rated temperature rise on the furnace nameplate. (typically 40 - 70 deg.)
- Temperature rise below maximum + Limit Trips = Bad Limit
- Temperature rise at or above maximum ⇒ Remove the air filter and recheck the temperature rise.
4. Check Gas Pressure
- Monitor the manifold gas pressure when gas valve opens.
- Natural Gas = 2.5" w.c. minimum to 3.5" w.c. maximum
- LP Gas = 9" w.c. minimum to 11" w.c. maximum
5. Check Duct Static Pressure
- Check the return static pressure (in the blower door if possible).
- Check the supply static pressure (between the furnace and evaporator coil if possible).
- High Duct Static = Above 0.5" w.c.
- High Return Static + Low Supply Static = Restricted Return Ductwork
- Low Return Static + High Supply Static = Clogged Coil or Restricted Supply Ductwork
- Compare static on both sides of evaporator coil.
- High Static Entering Coil + Low Static Leaving Coil = Clogged Coil
6. Check Limit Circuit
- Check for 24VAC between "24V Com" and the RED wire on Pin #1 of the 9-pin plug.
- Check for 24VAC between "24V Com" and the RED wire on Pin #7 of the 9-pin plug.
- Power on Pin #1 + Power on Pin #7 + Code 33 = Bad Control Board
- Power on Pin #1 + No power on Pin #7 = Open Circuit --> Check Each Switch
- Primary Limit
- Check for 24VAC between "24V Com" and both sides of the Primary Limit Switch.
- Power on Both Sides = Limit OK
- Power on One Side Only = Open Switch
- Heat Exchanger Cool = Bad Limit
- Heat Exchanger Hot ⇒ Allow time to cool and re-check.
- Rollout Switch
- Check for 24VAC between "24V Com" and both sides of the Rollout Switch(es).
- Power on Both Sides = Limit OK
- Power on One Side Only = Open Switch ⇒ Reset switch and Check Heat Exchanger!