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Discussion Starter #1
Hey guys, I have a 2005 6420 and I’m having problems with the a/c.
After a couple hours the air starts gradually getting warmer. It will start out around 40* and go up to above 55*. The suction line will be completely froze over at the low side gauge connection so I assume my evaporator is freezing up as well. I connected my gauges and the readings I got was 10 psi and 160 psi on a 85* day. The compressor will run constantly and not cycle off. Does this system have a low pressure cycling switch, if so where is it located? All I have found is a switch on the high side line after the dryer. Thanks in advance for any help.
 

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10psi sounds very low...sounds and acts like low on freon


low on freon means a leak.... very slow leak is probably a front seal on the compressor and will get worse over time but it could be elsewhere...if your not up on AC probably needs a visit from someone who is

as far as i know all ac compressors have a low pressure switch to keep them from running with no freon ....10psi should be very close to the lower limit .....possibly someone else can help with location

usually 3 things cause the compressor to not run..#1 low pressure....#2 high pressure...#3 no demand ....so at this point your probably meeting all the criteria for the compressor clutch to keep the compressor engaged and running
 

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Agreed. Suction line/evaporator freeze is a sign of low freon. Which means there still is freon in the system, which means a small leak. I don't know if JD sells AC leak stop, but you should be able to get some for the type of freon that's in your system (Autozone, Amazon, etc). I've had good luck before with systems that have a small leak. It can work really well for small leaks at o-rings (get you more years), and compressor shaft seals, but those usually only buy you some time and eventually need replacement.
 

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Agreed. Suction line/evaporator freeze is a sign of low freon. Which means there still is freon in the system, which means a small leak. I don't know if JD sells AC leak stop, but you should be able to get some for the type of freon that's in your system (Autozone, Amazon, etc). I've had good luck before with systems that have a small leak. It can work really well for small leaks at o-rings (get you more years), and compressor shaft seals, but those usually only buy you some time and eventually need replacement.
i agree on all you said .....stop leak is last resort for me i have visions of it clogging oriface tubes etc...but it might be a irrational fear i have :laugh:
 

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What I was taught is that it only hardens when exposed to oxygen, so it's safe when inside the system.
 
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There's no way I'd put stop leak in any of my AC systems. I've read several horror stories about adding it to AC system then system required a full flush. I wonder how clean the evaporater,condenser & cab filters are????
 

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To each their own.

So you've only read negative stories, and never any positive stories?
 

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I’ve seen it. Nope. Never. No stop leak products in any of my equipment. If someone asks me for help on something that was leaking and they used a stop leak product, I tell them they will probably end up replacing or deep cleaning the entire system it was used in. Too many times.... Never again.
 

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I would agree with the others as to the low charge. The pressures you report appear low, especially for an ambient temp of 85F.

Many system designs do not cycle the compressor on/off to regulate the evaporate temperature. Rather, they do so by metering the orifice in the expansion valve. There will typically be a capillary tube from the expansion valve to a sensor mounted in the evaporator with this design. Chrysler utilized this type of system for AC equipped vehicles in the '60s & '70s. Most residential systems operate in a similar manner.
 
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Discussion Starter #11
Thanks for all the replies, I too thought my pressures were a low indicating low freon but was unsure about the compressor running continuously. I figured it would be cycling on and off and didn’t know if there was some other switch that would cycle the compressor once the evaporator temp was cold enough. I will connect my gauges again and add Freon and report back.
 

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So I added freon and the pressures came up but so did the temperature coming from the vents. Low side was around 18-20 and high side was 250. Added a little more and low side was about 28 and high side went to over 350. And vent temperatures went up higher. So at this point I’m thinking maybe expansion valve stuck???? Both cab air filters are clean and condenser is clean. I checked the dryer for a restriction by feeling for a difference in temperature on the inlet and outlet line but they were pretty close to the same temp. Am I missing something???
 

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Can you be more specific as to air temp? Continues come up as running? Do you have one of those infrared point-aim-trigger thermostats? If so, point it at the suction line at the exits from the evaporator. What is the temp when when first turned on and then every minute for 10 minutes? If you don't have one, they're cheap.
 

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Update on my a/c problem. Had a friend come by that does a/c work and he said expansion valve was bad causing the system to freeze up. I changed it out and vacuumed and recharged system and it’s working correctly and not freezing up. Thanks for all the help you guys provided.
 

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Update on my a/c problem. Had a friend come by that does a/c work and he said expansion valve was bad causing the system to freeze up. I changed it out and vacuumed and recharged system and it’s working correctly and not freezing up. Thanks for all the help you guys provided.
thanks for the follow-up sometimes guys dont post cures and results which doesnt help others with the same possible problem :good2:
 
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