Goodman Furnace High Limit Switch Location and How to Access It

The high limit switch on a Goodman furnace is a critical safety device that prevents overheating by shutting off the burner or the blower when temperatures exceed safe limits. This article explains where to find the high limit switch on common Goodman furnace models, how to access and test it, signs that it is failing, replacement tips, and safety precautions. The guidance helps homeowners and technicians identify problems and make informed decisions about repair or replacement.

Goodman Model Series	Typical High Limit Switch Location	Access Notes
GMV, GMP	Near the heat exchanger on the blower housing, often on the front panel	Remove front access panel; switch often mounted with two screws
CPG/CGS	On the side of the furnace cabinet adjacent to the heat exchanger or on the plenum	Plenum removal or side panel needed for direct access
GMH, GMS	On blower housing or near the draft inducer area	May be recessed; check behind blower assembly

What Is The High Limit Switch And Why It Matters

The high limit switch is a temperature-activated safety control designed to open if the furnace internal temperature rises above a preset threshold. When the switch opens, it interrupts the gas valve or the control board signal to the burner, preventing potential overheating and equipment damage.

Key Functions: protects the heat exchanger from overheating, prevents potential fire risk, and stops the blower or burner to avoid further temperature rise.

Common Locations On Goodman Furnaces

Goodman furnaces share similar internal architectures, but locations for the high limit switch vary by model and cabinet design. Generally, the switch is mounted where it can accurately sense internal temperature near the heat exchanger or blower housing.

• Front Panel Near Heat Exchanger: Common for many single-stage upflow furnaces.
• Side Of Blower Housing: Often used when the blower assembly is separate from the burner compartment.
• Supply Plenum Or Returning Plenum: Some multi-speed or multi-position installations locate the switch near airflow transitions.

Step-By-Step: How To Locate The High Limit Switch

Locate the furnace identification plate and model number first, as this helps reference the service manual for exact switch placement.

Power Down The Furnace: Turn off power at the service switch and shut off gas supply before opening panels.

Remove Access Panels: Most Goodman units require removal of the front panel and possibly the blower access panel to expose the heat exchanger and blower housing.

Look For A Small Round Or Rectangular Sensor: The high limit switch typically appears as a small round metal or plastic-disc sensor with two or three electrical terminals and is often secured with screws or rivets.

How To Test The High Limit Switch Safely

Testing requires a multimeter and basic mechanical skills. If uncertain, contact a licensed HVAC technician.

1. Ensure Power Is Off: Confirm the furnace is completely de-energized and gas is shut off.
2. Locate The Switch And Disconnect Wires: Note wire positions or photograph them for reassembly.
3. Set Multimeter To Continuity Or Ohms: A closed switch at normal temperature should show near-zero resistance or continuity.
4. Check At Room Temperature: A functional limit switch reads closed at normal ambient conditions.
5. Simulate Heat (Optional And With Caution): Use a heat gun at a distance to raise temperature; the switch should open at its rated trip point. Only trained technicians should perform heat simulation near combustibles.

Symptoms Of A Faulty Or Tripped High Limit Switch

Recognizing symptoms helps diagnose whether the high limit is the root cause.

• Furnace Shuts Down During Heating Cycles: Intermittent burner cutouts indicate possible high limit trips.
• Blower Runs Continuously Or Not At All: Depending on wiring, the blower might be affected when limits change state.
• System Shows Error Codes: Goodman control boards may flash LED codes indicating high limit faults—consult the manual.
• Overheating Smell Or Warm Cabinet: Persistent heat or odor suggests restricted airflow causing repeated trips.

Common Causes For High Limit Trips And Failures

Understanding causes helps prevent recurrence after replacing a switch.

• Restricted Airflow: Dirty filters, closed vents, or blocked return ducts cause heat buildup.
• Blower Motor Problems: A failing motor or capacitor reduces airflow, causing overheating.
• Heat Exchanger Issues: Cracked exchangers or improper combustion airflow can alter internal temperatures.
• Faulty Switch Or Corrosion: Age, moisture, or mechanical wear can cause the switch to fail or stick.

Replacing The High Limit Switch: Tools, Parts, And Steps

Replacement is straightforward for many homeowners comfortable with basic appliance work; however, gas and electrical risks mean professional service is advised for most.

Tools And Materials: multimeter, screwdrivers, nut drivers, replacement limit switch (matched to model and temperature rating), wire connectors, and manufacturer’s parts diagram.

Replacement Steps: power off, label and disconnect wires from existing switch, remove mounting screws, install new switch in the same orientation, reconnect wires, restore power, and test operation by running a short heating cycle while monitoring for proper behavior.

Finding The Correct Replacement Part

Match the part number and temperature rating from the original switch or the furnace schematic. Goodman uses specific OEM part numbers; using exact matches ensures compatibility with mounting, terminal spacing, and trip temperatures.

If the original part number is unavailable, authorized Goodman distributors and HVAC suppliers can cross-reference compatible limits. Never substitute a limit switch with a different trip rating as it may bypass safety measures or cause nuisance trips.

When To Call A Professional HVAC Technician

Call a licensed HVAC technician if the fault involves gas valve wiring, suspected heat exchanger cracks, repeated trips after replacing components, or if the homeowner lacks tools and experience.

Technicians will perform combustion analysis, flue integrity tests, and airflow diagnostics to identify root causes and ensure safe repair and code compliance.

Maintenance Tips To Prevent High Limit Trips

Routine maintenance reduces the likelihood of limit switch trips and improves furnace performance.

• Change Air Filters Regularly: Replace filters every 1–3 months depending on use and filter type.
• Clean Registers And Return Vents: Ensure unobstructed airflow throughout the house.
• Schedule Annual HVAC Tune-Ups: Technicians will clean blower wheels, inspect heat exchangers, and verify controls.
• Check Blower Motor And Capacitor Health: Early replacement prevents airflow loss and overheating.

Safety Precautions And Best Practices

Safety is paramount when working with gas and electrical components.

• Always Turn Off Power And Gas Before Opening A Furnace.
• Use Insulated Tools And Avoid Metal Contact With Live Terminals.
• Label Wires Before Disconnecting To Ensure Correct Reassembly.
• If A Heat Exchanger Crack Is Suspected, Stop Using The Furnace And Call A Technician Immediately.

Additional Resources And Where To Find Schematics

Goodman furnace manuals and wiring diagrams are available on the manufacturer’s website and through authorized dealers. Model-specific service manuals provide exact component locations and replacement procedures.

OEM part distributors and HVAC forums can assist with cross-references and troubleshooting advice, but final repairs involving combustion or heat exchanger integrity should be done by certified professionals.

Quick Troubleshooting Checklist

Issue	Quick Check	Action
Frequent Limit Trips	Check filter and vents	Replace filter, clear obstructions, monitor
No Continuity On Switch	Multimeter test at room temperature	Replace switch with exact spec
Intermittent Blower Problems	Inspect blower motor and capacitor	Repair or replace blower components
Repeated Trips After Replacement	Inspect heat exchanger and airflow	Call HVAC technician for advanced diagnostics

How This Information Helps Homeowners And Technicians

Knowing the probable location of the Goodman furnace high limit switch speeds diagnosis, reduces unnecessary disassembly, and helps determine whether a simple parts replacement or full service is required.

Homeowners gain the ability to identify symptoms and perform basic checks safely. Technicians can use these guidelines to streamline troubleshooting and focus on root-cause analysis for persistent issues.