HS1P1S – HEAT SEQUENCER (SPST, Q101)

If your electric furnace is not heating or the blower timing is off, a failed heat sequencer could be the cause. This basic single-pole single-throw sequencer controls one circuit — either a heating element or a blower motor — on a timed delay.

Specs: 24V coil, SPST (single-pole, single-throw), thermal time delay

Replaces: NS101, Q101, SSEA34

Fits: Universal — electric, gas, or oil furnaces requiring a basic SPST heat sequencer

In stock at Open To Public HVAC Parts in Dallas. We test parts at the counter before you buy. Call or text (214) 340-9421.

Specs

• TypeElectric heat strip sequencer
• Pole ConfigurationSPST
• Coil Voltage24V AC
• Delay30-90 seconds between stages (typical)
• OEM CompatibilityUniversal

Cross-reference numbers

This part replaces the following OEM and aftermarket numbers:

• NS101
• HS1P1S
• Q101

Not sure if your number matches? Call (214) 340-9421 or bring the old part in — bench-testing is free.

Fits these models

• Universal aftermarket heat sequencer — staggers electric heat strip energization on residential and light-commercial electric heat kits
• Common applications: Rheem RXBH / RXMS / RXST, Goodman HKS, First Co H1830, Carrier KFCEH, Trane heat kits
• Match pole configuration (SPST/DPST/DPDT/TPST) to your existing sequencer; cross-reference part number with your heat kit's wiring diagram

How does a heat sequencer work?

A small bimetallic heater inside the sequencer gets 24V on a heat call from the thermostat. The heat slowly warms a bimetal disc that closes successive contact sets over 30-90 seconds — energizing each heat strip in sequence to prevent a simultaneous current spike that would trip the breaker.

How do I test a heat sequencer?

Apply 24V to the coil terminals (no load). Wait 30-90 seconds — you should hear individual contacts click closed in sequence. Use a multimeter for continuity across each load terminal pair. If one stage never closes, replace.

SPST vs DPST vs DPDT vs TPST — what's the difference?

- SPST = single pole, single throw (1 contact set, switches 1 strip) - DPST = double pole, single throw (2 contacts, switches 2 strips simultaneously) - DPDT = double pole, double throw (2 contacts with NO + NC positions) - TPST = triple pole, single throw (3 contacts, switches 3 strips simultaneously)

Why won't my heat strips come on?

Test the sequencer first — bad sequencer = no signal to the strips. Also check: thermostat call on W terminal, 24V at sequencer coil during heat call, line voltage on strip side, intact heater elements (continuity test each strip).