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SportTrac Discussion
General Sport Trac Discussion
Heat Only Works When Accelerating
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<blockquote data-quote="Dan Long" data-source="post: 1024130" data-attributes="member: 65387"><p>It definitely sounds vacuum related, and the cause is likely the heater core bypass valve that's installed in one of the lines near the firewall. This valve stops the flow of coolant into the core to help the A/C work better when on the Max A/C setting, hence the reason you can't get warm air on that setting regardless of the temperature selector position.</p><p></p><p></p><p></p><p>I've never investigated the exact operation of that valve, but my guess is that when it sees vacuum, it closes off. You likely do have a faulty vacuum reserve ball, because when accelerating you lose vacuum. Typically the other thing you'll notice when it goes bad is that when the engine is under heavy, prolonged load that the dash vents will change to the defroster vents until you let off the gas and the engine builds vacuum again, because the vent selector door is also vacuum operated.</p><p></p><p></p><p></p><p>Options are either fix the vacuum leak or reserve ball, or just remove that bypass valve and cap off its vacuum line connection.</p></blockquote><p></p>
[QUOTE="Dan Long, post: 1024130, member: 65387"] It definitely sounds vacuum related, and the cause is likely the heater core bypass valve that's installed in one of the lines near the firewall. This valve stops the flow of coolant into the core to help the A/C work better when on the Max A/C setting, hence the reason you can't get warm air on that setting regardless of the temperature selector position. I've never investigated the exact operation of that valve, but my guess is that when it sees vacuum, it closes off. You likely do have a faulty vacuum reserve ball, because when accelerating you lose vacuum. Typically the other thing you'll notice when it goes bad is that when the engine is under heavy, prolonged load that the dash vents will change to the defroster vents until you let off the gas and the engine builds vacuum again, because the vent selector door is also vacuum operated. Options are either fix the vacuum leak or reserve ball, or just remove that bypass valve and cap off its vacuum line connection. [/QUOTE]
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SportTrac Discussion
General Sport Trac Discussion
Heat Only Works When Accelerating
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