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Trouble With A/c On 99 Ch613


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the a/c went out on the first day of wheat hauling. the clutch on the compressor quit engaging so i checked all the fuses and everything was ok there. I do not have any power coming down the the clutch or the low pressure switch(the mack guy said it does both, he called it a binary switch) $54 new, by the way). i hot wired it today from a wire of my pick up battery and it works fine. (but i also have to run a ground from my truck battery to the compressor to make fire go through the hot wire..dont know if that is normal or not. also the ref. is not low.

i thought about hot wiring power to the clutch and low pressure switch and putting an inline fuse in there. bad idea? what would be the cause of no power coming to the clutch or low pressure switch if all the fuses are good?

thanks!!

Edited by king cotton
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the a/c went out on the first day of wheat hauling. the clutch on the compressor quit engaging so i checked all the fuses and everything was ok there. I do not have any power coming down the the clutch or the low pressure switch(the mack guy said it does both, he called it a binary switch) $54 new, by the way). i hot wired it today from a wire of my pick up battery and it works fine. (but i also have to run a ground from my truck battery to the compressor to make fire go through the hot wire..dont know if that is normal or not. also the ref. is not low.

i thought about hot wiring power to the clutch and low pressure switch and putting an inline fuse in there. bad idea? what would be the cause of no power coming to the clutch or low pressure switch if all the fuses are good?

thanks!!

I don't know about your truck but in automobiles the a/c clutch is actually pulled in by the engine ECM. If the truck is like cars, you will either need to flash the ECM, or disconnect the batteries for about 30 seconds to dissolve the latched fault code.

The a/c system is prolly low on refrigerant and this caused it to be locked out as a precaution. I would not external power the clutch until you know the system has no other faults. If it is low on charge, it can't oil itself and if forced to run, destruction of parts soon follows.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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I don't know about your truck but in automobiles the a/c clutch is actually pulled in by the engine ECM. If the truck is like cars, you will either need to flash the ECM, or disconnect the batteries for about 30 seconds to dissolve the latched fault code.

The a/c system is prolly low on refrigerant and this caused it to be locked out as a precaution. I would not external power the clutch until you know the system has no other faults. If it is low on charge, it can't oil itself and if forced to run, destruction of parts soon follows.

Rob

Yes, most new vehicles are like this. If the system thinks it is low on freon it won't let the compressor engage. On the newer Freightliners, the compressor does try to run for a short period of time before it quits. Not sure if the Macks are the same way.

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I don't know about your truck but in automobiles the a/c clutch is actually pulled in by the engine ECM. If the truck is like cars, you will either need to flash the ECM, or disconnect the batteries for about 30 seconds to dissolve the latched fault code.

The a/c system is prolly low on refrigerant and this caused it to be locked out as a precaution. I would not external power the clutch until you know the system has no other faults. If it is low on charge, it can't oil itself and if forced to run, destruction of parts soon follows.

Rob

my brother put his gauges on it and said it might be a 1/2 low. he works for CAT as a field mech. woulndt the clutch stay engaged all the time when it 95 and heat index of 105? i understand about no lubrication due to low 134-a.

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my brother put his gauges on it and said it might be a 1/2 low. he works for CAT as a field mech. woulndt the clutch stay engaged all the time when it 95 and heat index of 105? i understand about no lubrication due to low 134-a.

Depends on the calibration of the cutout switch. What you referred to as a "binary" switch. This simply means on or off.

I think you know the direction to follow at this point.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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rob, i am assuming i know the proper direction to follow, but will you spell it out please? you know what assumtion does!! i am guessing i need to follow the 1000nd wires that the clutch and binary switch wires feed into and see where they are losing power at...1000nd wires...shouldnt take too long!! thanks for the help

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rob, i am assuming i know the proper direction to follow, but will you spell it out please? you know what assumtion does!! i am guessing i need to follow the 1000nd wires that the clutch and binary switch wires feed into and see where they are losing power at...1000nd wires...shouldnt take too long!! thanks for the help

I think the system is too low on refrigerant myself. I would disconnect the batteries for about a minute, then reconnect with gauges and refrigerant plumbed into the system ready to start the charge cycle.

What I typically do is connect my charging apparatus, turn on the refrigerant source until I see about 75psi on the low side gauge via the high side using liquid refrigerant through the charge port. After letting the liquid "flash" to gas for about a minute, I enable the a/c system and finish charge with gas through the low side suction port. Typically I look for about a 33-35 degree evaporator temperature, (by the charging gauges as I don't look for pressure) and about a 51-55 degree discharge air temperature from the duct nearest the evaporator inside the truck for a properly sized system. As the outside ambient temperature increases, so does head pressure so I don't rely solely on pressure other than a reference. Do try to stay under 275psi on the head pressure however as it is easy to overcharge and if lucky and safetys are working correctly the binary switch on the high side will cut out.

Besides the engine mounted fan, I use a large box fan to keep air moving across the heat exchanger, (condensor) to remove the heat of absorbtion, and compression/operation.

Rob

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Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Here is a diagram for a CH/CL from 2000 without APADS diagnostic module. This is most likely the way your truck is wired. If you follow the wiring from the A/C compressor back you will see that it goes through the HVAC panel. On the diagram, to the left of the blower motor, there is an item that is not labeled. This is the freeze switch (aka thermocouple). It opens and closes depending on the temperature of the evaporator core in order to cycle the compressor clutch in and out so as to keep the system from freezing up. If it is open all the time the compressor clutch will not recieve power from fuse 28. The freeze switch is located in the HVAC panel behind the controls. There should be a long flexible shaft on the end of the switch that is pushed into the evaporator core.

Air Conditioning Diagram.pdf

"Mebbe I'm too ugly and stupid to give up!"

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rhasler,

coud you repost or email me that diagram with what you are talking about circled or a big arrow pointing to it? i dont see the item to the left of the blower motor on the diagram. i know this is like pulling teeth and i apologize, if you dont know, you dont know!

thanks.

skylerhays@gmail.com

Edited by king cotton
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rhasler,

coud you repost or email me that diagram with what you are talking about circled or a big arrow pointing to it? i dont see the item to the left of the blower motor on the diagram. i know this is like pulling teeth and i apologize, if you dont know, you dont know!

thanks.

skylerhays@gmail.com

No Problem.

Air Conditioning Diagram.pdf

"Mebbe I'm too ugly and stupid to give up!"

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  • 2 weeks later...

I think the system is too low on refrigerant myself. I would disconnect the batteries for about a minute, then reconnect with gauges and refrigerant plumbed into the system ready to start the charge cycle.

What I typically do is connect my charging apparatus, turn on the refrigerant source until I see about 75psi on the low side gauge via the high side using liquid refrigerant through the charge port. After letting the liquid "flash" to gas for about a minute, I enable the a/c system and finish charge with gas through the low side suction port. Typically I look for about a 33-35 degree evaporator temperature, (by the charging gauges as I don't look for pressure) and about a 51-55 degree discharge air temperature from the duct nearest the evaporator inside the truck for a properly sized system. As the outside ambient temperature increases, so does head pressure so I don't rely solely on pressure other than a reference. Do try to stay under 275psi on the head pressure however as it is easy to overcharge and if lucky and safetys are working correctly the binary switch on the high side will cut out.

Besides the engine mounted fan, I use a large box fan to keep air moving across the heat exchanger, (condensor) to remove the heat of absorbtion, and compression/operation.

Rob

MackAttack3

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Rob, would you mind telling me how you mounted box fan to blow thru condensor. I would like to try that. This 105 heat index is tough, to say the least. Thanks

Hi there, I don't mount the fan at all. I just set it on a stand near the front of the vehicle.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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