A/C will cycle the engine fan on and off to control the A/C system high side pressure. If the fan comes on at highway speeds with the A/C on (and stays off with the A/C off) the first thing I'd look at is the condensor (usually up front with the radiator). Usually over the years the fins get folded over and it restricts airflow through it. If the air flow can't take the heat out of the condensor, A/C high side pressure climbs up and kicks the fan on to try and pull the heat out of the condensor core.
99 Classic multiple questions
Discussion in 'Freightliner Forum' started by shakerclassic, Jun 10, 2018.
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Ha oh yeah having too much fun! I don't think the speed sensor is messed up. I noticed the wires from the sensor that go to a plug (i'm assuming) were ripped out? I'm still trying to locate where a plug would be around the trans but haven't found one yet.
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Alright that is some very useful information. I'll have to check that out tuesday when my next chance will be. Part of me is wondering about a thermostat but with the AC off it will get on up to about 185-190 and I usually will flip the switch in cab to turn fan on just to keep it from getting too warm.
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I do believe its cycling on and off not 100% about that though) I just felt like the operating temp was too low. All the other trucks i've driven have ran about 180-190.
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I'm gonna check out some of this stuff tuesday when I get some free time. How would you tell if it is a 2 speed fan? I personally haven't ever heard of that. I thought the temps were low and when the AC is off it will climb up to 185-190 and then I usually flip the fan switch in cab since I really don't want to melt it down.
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Your low air indicator switch is stuck closed or not screwed into a live air port.
If you have ABS your speedo is likely using the ABS sensors to measure your speed, if the ABS light is on then change your wheel speed sensors and see if the speedo starts working.
Your A/C is overcharged if the engine fan runs constantly with the A/C on, or somebody jumped the A/C compressor power line to the Horton fan switch (I have seen guys do this but there is no good reason for it).
I agree that the blower resistor is why you only have high speed but I usually change the blower motor when I lose a resistor, it is usually a high amp condition in the blower motor that fries the resistor in my experience.shakerclassic Thanks this. -
I missed the part where you found a ripped up plug.
Your transmission speed sensor is located at the rear of the transmission where the yoke slides in, it is held in by one small bolt. If the wires got ripped out you can buy a new speed sensor with a plug pretty cheap and just reconnect it. -
Well as far as the speed sensor goes there's still a good bit of wire coming out of the sensor (probably 4-5") and what I was thinking I would try to do is rewire them to the truck side connector but I can't find one anywhere around the transmission on either side or on top. If I have to I'll just run new wire up to the speedometer just figured repairing just in that area would be easier if i knee where the plug was.
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