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SportTrac Discussion
General Sport Trac Discussion
Heat Only Works When Accelerating
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<blockquote data-quote="Richard L" data-source="post: 1024136" data-attributes="member: 52972"><p>stanner,</p><p></p><p>If the vacuum canister is leaking it would default to Heat only</p><p></p><p></p><p></p><p>The reason why the heat shuts off at idle is because that is when the engine is generating the most vacuum. Wider throttle settings reduce available vacuum, and that is what the reserve vacuum canister is for...to hold vacuum during periods of low intake vacuum.</p><p></p><p></p><p></p><p>So at Idle the engine is creating enough vacuum to overcome the canister leak and still hold the heat door closed. When accelerating, the throttle is opened and engine vacuum drops to it's lowest level. If the canister is leaking, there is little or no reserve vacuum and the heater door opens to it's default setting.</p><p></p><p></p><p></p><p></p><p></p><p>PS: gopack,</p><p></p><p>There is also a check-ball valve where the engine vacuum line attaches to the canister (ball) to hold vacuum when the engine is not producing much vacuum. If the check-ball sticks or fail, you can lose vacuum even though there is no cracks or leaks in the canister. You usually cannot fix or replace the check-ball, so its best to just replace the canister.</p><p></p><p></p><p></p><p>...Rich</p></blockquote><p></p>
[QUOTE="Richard L, post: 1024136, member: 52972"] stanner, If the vacuum canister is leaking it would default to Heat only The reason why the heat shuts off at idle is because that is when the engine is generating the most vacuum. Wider throttle settings reduce available vacuum, and that is what the reserve vacuum canister is for...to hold vacuum during periods of low intake vacuum. So at Idle the engine is creating enough vacuum to overcome the canister leak and still hold the heat door closed. When accelerating, the throttle is opened and engine vacuum drops to it's lowest level. If the canister is leaking, there is little or no reserve vacuum and the heater door opens to it's default setting. PS: gopack, There is also a check-ball valve where the engine vacuum line attaches to the canister (ball) to hold vacuum when the engine is not producing much vacuum. If the check-ball sticks or fail, you can lose vacuum even though there is no cracks or leaks in the canister. You usually cannot fix or replace the check-ball, so its best to just replace the canister. ...Rich [/QUOTE]
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SportTrac Discussion
General Sport Trac Discussion
Heat Only Works When Accelerating
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