22 Main limit open

What the control is telling you

Main high-limit circuit is open (supply air too hot / poor airflow). 802P/R95P: if open more than 150 seconds during a heat call, 61 and 22 alternate (dead blower) until it recloses. RGPE/RGLE: an open main limit can indicate excessive duct static; thermostat shows Call For Service / CHECK FURNACE.

Applies to: 802P/80MDP (802PA050-150); R95P (R95PA040-115); RGPE/RGLE 2-stage 80+

Likely causes

• Dirty or restricted filter or cooling coil
• Closed registers/dampers, undersized or restricted ducts, high static
• Blower problem: wrong speed tap, bad capacitor, dirty wheel, failing motor, low voltage
• Overfiring (high gas pressure, wrong orifice)
• Loose limit wiring

Test and repair steps

1. Replace the filter and check the A/C coil and blower wheel for dirt.
2. Check registers/dampers are open and ducts are adequate.
3. Verify the blower runs on heat speed; check speed tap, capacitor, wheel and motor (RGPE/RGLE: ECM blower, see 60/61).
4. Measure temperature rise and compare with the rating plate range.
5. RGPE/RGLE check rise at both low and high fire; adjust SW3-1/SW3-2 heat rise if outside range.
6. Check manifold pressure and orifice size for overfiring.
7. Check wiring between IFC and all limits; replace a limit that is open at normal temperature.

Settings for these units

• Clearance to combustibles (all models) · R95P
• Filter sizes as shipped, upflow (Table 19) · RGPE/RGLE
• Reduced clearance to combustibles, upflow/horizontal (Fig. 4) · Rheem/Ruud 802P / 80MDP 80% two-stage furnace (UT 1028-928 IFC)
• Reduced clearance to combustibles (Fig. 3 and 4) · RGPE/RGLE