M.C. Enterprises 31377MC Furnace Low Air Flow Switch (Sail Switch)

Aftermarket Replacement for Dometic / Atwood 31377

Part Number: 31377MC
Replaces: Dometic / Atwood 31377
Product Type: Furnace Low Air Flow Switch (Sail Switch)
Application: Atwood & Dometic HydroFlame Furnaces

Product Overview

The M.C. Enterprises 31377MC Furnace Low Air Flow Switch is a high-quality aftermarket replacement designed to replace Dometic / Atwood OEM Part 31377.

Also known as a sail switch, this component verifies adequate blower airflow before permitting the furnace ignition sequence. If proper airflow is not detected, the switch prevents ignition to protect against improper combustion.

If your RV furnace blower runs but the burner will not ignite, cycles erratically, or shuts down prematurely, a failed sail switch is one of the most common causes.

Replacing your original 31377 sail switch with the 31377MC restores proper ignition sequencing, stable airflow monitoring, and reliable heating performance.

Manufactured by M.C. Enterprises, this component provides dependable performance and direct-fit compatibility for a wide range of Atwood and Dometic furnace models.

Key Features

• Direct aftermarket replacement for Dometic / Atwood 31377
• Verifies airflow before ignition
• Helps resolve “blower runs but no heat” issues
• Restores proper ignition sequencing
• Direct-fit design for compatible furnace models
• Cost-effective alternative to OEM

Compatible Furnace Models

7900 & 7900-II Series

7912
7912-II

7916
7916-II

7920
7920-II

8500 Series

8516
8516-II
8516-III
8516-IV

8520
8520-II
8520-III
8520-IV

8525
8525-II
8525-III
8525-IV

8531
8531-II
8531-III
8531-IV

8535
8535-II
8535-III
8535-IV

8900 Series

8935 Models

8935-DC-I
8935-AC-I
8935-DC-II
8935-AC-II
8935-DC-III
8935-AC-III

8940 Models

8940-DC-I
8940-AC-I
8940-DC-II
8940-AC-II
8940-DC-III
8940-AC-III

Always verify your furnace model number and confirm it originally used Part 31377 before ordering.

When Should You Replace the Sail Switch?

You may need to replace the sail switch if:

• Blower motor runs but burner does not ignite
• Furnace attempts ignition then shuts down
• Heating is intermittent
• Airflow-related shutdown occurs
• Paddle is stuck, bent, or contaminated

The sail switch is one of the most common service parts in HydroFlame furnaces.

Product Specifications

Manufacturer: M.C. Enterprises
Part Number: 31377MC
Replaces: Dometic / Atwood 31377
Component: Low Air Flow Switch (Sail Switch)
Application: 7900, 8500 & 8900 Series Furnaces
Includes: Sail switch assembly

Frequently Asked Questions (FAQ)

Q: Is this an OEM Dometic part?
A: No. This is an aftermarket replacement manufactured by M.C. Enterprises that replaces OEM part 31377.

Q: What does a sail switch do?
A: It confirms adequate airflow before allowing the burner to ignite.

Q: Will this fix a furnace where the blower runs but no flame appears?
A: A failed sail switch is one of the most common causes of that issue.

Q: Is this compatible with both AC and DC models?
A: Yes, as listed above, it fits applicable AC and DC 8900 models that originally used 31377.