Question about 1999 Dodge Ram

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Hi I have purchased a 1999 Dodge Ram 3500 van and the motor run fine, but when I turn on the a/c, the motor acts sluggish and eventually cuts off. I noticed that there was a switch installed to the dash board that leads to the ac unit, but no one knew what it was for? When you turn the switch on, it makes a loud fan noise. What would cause the air to make the motor run bad? It only runs bad when the a/c is on. The conpressor kicks on when I had some freon added, but after five minutes of the air blowing, it got hot again.

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IT sounds like someone has installed a manual fan switch in you truck. This was done either because the fan relays were faulty or because of a wiring issue. The reason behind the poor performance is likely to be several different things. But in order to check this out thoroughly you should have the engine codes read first. This can be performed at you auto parts store like Autozone or Oriellys. Once you have the engine diagnostic codes this will tell you if you have a faulty sensor. The other reasons for poor performance is due to the engine temp increasing from the A/C running and the Electric fans not cooling the motor. A hot engine will perform very poorly with a lack of power and hesitations. This is because the engine is so hot that the fuel being sprayed into the manifold is being partially burnt before it's used in the combustion chambers. Another cause is called vapor lock. When the fuel lines become so hot the fuel inside them actually turns from a solid into a vapor, when this happens you get a greatly reduced amount of fuel pressure which can cause the vehicle to die or stammer. Making sure that you have a properly cooled engine will help cure most of this. By the way, you should have that fan switch in the on position at all times if the real fan relay is not functioning.

Posted on Aug 03, 2010


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