SureTrack Community Fix: Hot and Cold FJ

Real Fixes from the SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is currently available free with the purchase of a current Snap-on® diagnostic software version.

Vehicles with multiple zone HVAC systems often have problems with heat distribution. But what do you do when it’s a single zone system and heat is only coming out of one side? SureTrack community member JOSH STEPHENSON had a Toyota FJ Crusier that would only put out heat on the driver side of the vehicle. They posed the question to the community, and with the help of fellow community member DAG1365 and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

2012 Toyota FJ Cruiser 4.0L

Hot and Cold FJ

Customer complains that heater blows hot on left and cold on right.

Diagnostic Steps Performed/Parts Replaced
Vehicle is equipped with manual single-zone HVAC. Came in with low temperature output from vents. Vehicle took more than 30 minutes to come up to operating temperature, passenger side never blows warm air. Using temperature gun measured temp at upper and lower hose and found temperatures remained close to same temperature. Compared to readings from coolant temperature sensor and found similar. Removed thermostat, verified that it was stuck open. Installed new thermostat and verified engine came up to operating temperature within 15 minutes. Checked heater inlet and outlet found them to be the same as coolant temperature. Checked duct temperature and found hot on left side and cool on right side. Checked blend door actuator and found actuator moving with full motion range. Switched to A/C, found left side warm and right side cold. I think I have a broken blend door or debris problem. Wondering if anyone has run across this or any additional diagnostic steps I can take before I pull the HVAC box.

Best Answer from Community Member DAG1365
Have you back flushed the heater core? Have had one side hot and other cold due to heater core being stopped up.

Debris from extremely worn radiator hoses plugged up back half of heater core. Heater box has a ridge inside that separates left from right causing the cold temp on right and hot on left.

Replaced radiator hoses and heater core. Verified both sides came up to temperature. Thanks for all the input.

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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.