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AC clutch only engages with jumped low pressure switch

302w

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1999 Mountie
I had ~40 PSI on my low pressure side but no AC. I bought a low pressure switch on a whim and put it in.

As of now, my pressure will rise to about 45 PSI, the AC clutch will engage for a second, disengage and drop the pressure, and continue doing so.

Playing around with different combinations of open/jumped contacts on the high pressure sensor plug yielded nothing. Clutch will not engage.

Clutch will engage and stay engaged with jumped low pressure contacts. I'm leery of running this for more than 10 seconds or so, so I cant tell if it's cooling the cabin.

What am I looking at wrong?

I do not have high pressure gauges. I'm using a cheap auto zone 134A hose and it says the pressure is normal for the ambient temperature

Thanks!
 



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shucker1

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I would not worry about running low side pressure with a bypass to see if the cabin is cooling.

On an extended basis yes it could cause harm to the compressor.

What is you low side pressure at the gauge when the clutch is on and running?
 






974X4BLACKSPORT

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You really need to know what the high side is doing too when the compressor is engaging.
 






302w

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My low side pressure will slowly build without the compressor on, then the pressure drops to 0 on the low side when the compressor kicks in.

As I type this... I wonder if I'm simply too low on refrigerant! I'll jump the compressor and try again.

Edit: Yup, I'm right and I feel like a fool. Thanks everyone!
 






shucker1

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Only way to find out is ask questions.

Next time you will know.
 






974X4BLACKSPORT

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Drops to zero equals blockage!
 












974X4BLACKSPORT

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Dont run you compressor without a gauge on the high side pressure port, I say this because if the pressure on the low side rapidly goes to "0" when the compressor engages, there is a good chance there is a blockage or severe restriction somewhere, probably on the high side going into the expansion/orifice valve. If the refrigerant cant go through the evaporator fast enough, or at all, then to much pressure will build on the high side and severe damage could result.
I am not saying this IS your problem, but just a theory on what I have understood in the posts above. Need more information (high pressure) reading.
 






koda2000

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Dont run you compressor without a gauge on the high side pressure port, I say this because if the pressure on the low side rapidly goes to "0" when the compressor engages, there is a good chance there is a blockage or severe restriction somewhere, probably on the high side going into the expansion/orifice valve. If the refrigerant cant go through the evaporator fast enough, or at all, then to much pressure will build on the high side and severe damage could result.
I am not saying this IS your problem, but just a theory on what I have understood in the posts above. Need more information (high pressure) reading.

I agree and if there's a blockage it's most likely because your compressor is worn out and throwing debris into the system clogging the orifice tube. If this is the case the entire system will need to be taken apart, flushed and the compressor, accumulator, expansion/orifice valve will need to be replaced and perhaps the condenser too. If you go through this expense adding an in-line filter is also cheap insurance.
 






8TZX

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I had a similar problem with my 99 XLT AWD. The compressor was continually short cycling due to low refrigerant. I did have a manifold gauge set and my high side would only get to about 100 psi and the low pressure cut-out would shut the compressor down. I had to add 2 cans of R-134 until I could keep the compressor running long enough to stabilize and fully charge. I did use a can of AC Super Seal and topped off the refrigerant which included an oil charge. This was done last August and I still have a decent evaporator temperature of 46 F at outside air of 85 F.
 






8TZX

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I forgot to add that when the system is very low on charge it's a good idea to submerge the can of refrigerant in hot water. This allows the refrigerant to flow faster into the system. This is necessary because the short cycling of the compressor prevents a "normal" draw of refrigerant from the can. Make sure you add refrigerant ONLY on the low side and don't turn the can upside down. You don't want to "slug" the compressor with liquid.
 






ranger7ltr

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I had ~40 PSI on my low pressure side but no AC. I bought a low pressure switch on a whim and put it in.

As of now, my pressure will rise to about 45 PSI, the AC clutch will engage for a second, disengage and drop the pressure, and continue doing so.

Playing around with different combinations of open/jumped contacts on the high pressure sensor plug yielded nothing. Clutch will not engage.

Clutch will engage and stay engaged with jumped low pressure contacts. I'm leery of running this for more than 10 seconds or so, so I cant tell if it's cooling the cabin.

What am I looking at wrong?

I do not have high pressure gauges. I'm using a cheap auto zone 134A hose and it says the pressure is normal for the ambient temperature

Thanks!
Find your refrigerant leak...Somewhere in your a/c system you have an oily section of hose,fitting, or rusty accumulator if you are lucky...Or the evaporator is leaking if you are not lucky...And borrow the proper tools if you can't buy them...

Running a leaky system will starve it for oil since the leak causes oil to leave with the refrigerant and the refrigerant runs through but the oil doesn't...Jumping the low pressure switch tells you at a minimum you are low on refrigerant...That doesn't tell the whole story though...On a Ford a/c system the compressor running with low or no lubrication will eventually experience Black Death...Google it and see what fun that is to fix...

The low pressure reading is only telling you approx what the evaporator running temp would be in a running system...The high side tells you how well the system is running and what shape the system is in...Clogged condenser on the outside [low or lack of airflow], dirty or plugged orifice tube, weak or worn compressor, and blend door issues will show up as high or low pressures on the high side...The low side you are seeing on the kit you have is the system pressure on both sides before you jumper the low pressure switch...With real gauges you would be able to see if both sides are the same pressure before you start[good] or if you have a restriction or blockage in the system [bad] and you have other work to do...

But if you want to fix this system the right way and not cause other problems get the proper tools and do some investigation to find out the cause of the problem.If you have an Autozone you can use their loan a tool program and then return the tools and be out no money at all...You are only renting them and you get your deposit back when you return them...

There are a lot of folks here that are knowledgeable and more than willing to help you get your Explorer working right so please don't hesitate to ask questions when you find issues...
 






masospaghetti

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I would get a proper manifold set with high and low side gauges. They are not that expensive ($115 will get you a decent name brand one from Amazon, such as Yellow Jacket) and this stuff pays for itself quickly - getting a system just "topped off" at a garage with 1 lb of refrigerant often will cost more than this.

https://smile.amazon.com/Yellow-Jac...jacket+r-134a&qid=1558456448&s=gateway&sr=8-2

R-134a cans can often be found for $5 or less if you are saavy online, or easily less than $10 at Walmart. This A/C repair is, IMO, really low hanging fruit to saving some money working on your own vehicle.
 






koda2000

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I would get a proper manifold set with high and low side gauges. They are not that expensive ($115 will get you a decent name brand one from Amazon, such as Yellow Jacket) and this stuff pays for itself quickly - getting a system just "topped off" at a garage with 1 lb of refrigerant often will cost more than this.

https://smile.amazon.com/Yellow-Jac...jacket+r-134a&qid=1558456448&s=gateway&sr=8-2

R-134a cans can often be found for $5 or less if you are saavy online, or easily less than $10 at Walmart. This A/C repair is, IMO, really low hanging fruit to saving some money working on your own vehicle.

Last time I noticed, my Walmart had R134A for around $6-$7 a can and Fred's carried it for around $5. You can get a less expensive set of A/C gauges from Harbor Freight for around $60.
Search Results For "a/c manifold gauge set"
 






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