Real Fix: Wrong Direction

Aug. 31, 2017

There is still enough summer left need to stay cool, and auto repair shops are filled with vehicles with air conditioning problems. But have you ever come across a vehicle where the air would come out of the defroster vents when stepping on the gas? This is conundrum one technician faced when their customer brought in a 2007 Ford Econoline E350 Super Duty 5.4L. Let’s see how this technician was able to solve the problem.

Diagnosis

After inspection, the technician found when the control is on Vent, A/C or Max and the engine is put under a load, the defrost vacuum actuator starts moving and the air flow goes to defrost. When he let off on the load, the defrost actuator had returned to allow air out of the vents. The technician responded with a visual inspection and a smoke test on the intake system, brake booster and HVAC system. No leaks were found. Frustrated, he turned to his SureTrack Community.

His fellow member commented that when air flow switches to the defrost position, it means vacuum is lost in the system. He recommended checking that all mode door positions were at idle. This makes sure a blend door motor vacuum line isn’t disconnected. Also, there is a vacuum canister under the heater box in the engine compartment that has a check valve which can go bad. When the supply vacuum goes away, the valve closes, and the vacuum canister holds the mode door positions. For this, the technician can buy the replacement parts or redo the system with aftermarket parts. After performing a smoke test from control to intake, he found the vacuum canister and check valve were leaking.

Fix

With the advice from the community member, the technician replaced the vacuum canister and check valve. At last! The Vent control is working as it should.

Real Fixes from Mitchell 1’s SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions. Read the Real Fix in the Mitchell 1 ShopConnection Blog.

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