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Flushing the evaporator


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I need to flush my evaporator and I am wondering if anyone has any experience doing this? The problem that I see is how to backflush. I have never flushed an AC system so any help will be appreciated. I am assuming that I have to take the expansion valve out of the system.  can pull the existing expansion valve and flush the #10 line going to the firewall but how do I flush the other direction? How do I insure the flushing liquid goes thru the evaporator coils before it exits back toward where the drier hooks up? Do I need the make a fake expansion valve the will have a barbed end to attach the flushing solution to and the other end machined to bolt into the expansion valve cavity so it directs the flushing solution to the approximately 5 or six evaporator lines? 

Please  ignore the two picture below if the show up. I somehow got them on this post and I can't figure out how to edit them out.

 

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Edited by Cruzzar
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Out of interest ... why do you feel the need to flush the evaporator?   You have a new compressor, condenser, & drier, if you kept the system sealed up and not exposed to the atmosphere and the old compressor was not sending chunks of debris thru the system, if it were me, I would leave it alone.   Just draw a vacuum down for a few hours to remove any moisture.    Just my non ac expert opinion.... 

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I kinda have the same question... Removing the other parts did you notice problems (buildup/gook) inside? (I've seen - and cleaned - A/C systems that haven't been treated well, and they can get some pretty nasty sludgy gook built up inside...) And why a "backflush" rather than just a flush using A/C Cleaner/Flush through the normal refrigerant path? Do you suspect the expansion valve is plugged? The expansion valve Nissan used is pretty odd and there are multiple paths through the evaporator. Since it's not a straight shot - and liquids (including air) follow the path of least resistance - parts of the evap may not get cleaner through them. Personally, I'd leave everything inside the cabin as-is and flush through the liquid and suction lines at the firewall. You could always try a backflush through the suction line there and see what pushed out the liquid line I guess. 

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My understanding is that the original compressor oil is not compatible with the new pag oil for the 134a. If the mix they have a tendency to coagulate. Do you think if I try to flush with the expansion valve in place that I will get enough volume of cleaner to flush out any remaining oil in the evaporator. The system has always had pressure in it, I am making the change because the original  Hatachi compressor was starting to make noise. I don't know what the origin of the noise was but I did not want to chance it plugging up the expansion valve because of its unobtanium supply. I am open to all comments?

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I have read on the internet (for what that is worth) that Ester oil is compatible with both PAG and Mineral oil (the stuff used with R-12). So maybe a retro fit (that is where you reuse at least one thing like the evap) should use Ester. Another reminder is to change out the hoses for barrier hoses (again a internet piece of info) as supposedly R-12 hoses will allow smaller molecule gases to pass thru. IF I ever switch out for R-134a my plan is to go with all new stuff, including the evap. I have a new evap that uses a standard commonly used expansion valve. Its all alum just like the orig. With that I would go to a PF condenser, hoses and new compressor and of course a generic drier. That being said, The R-12 in my car is still working fine after 5 years since I got the car, the compressor is noisy has been for 5 years and needless to ssy I use it a lot in Florida. The noise has not changed in my ownership. My plan is to leave it be, if it goes then I will do the complete job. As far as flushing the evap, sounds like a good idea if you want to be sure, but the bigger issue is that darn expansion valve. Honestly I would just pop for the new unit, its about 400$ IIRC.

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Dave, I am replacing: the compressor, the condenser with a PF unit from Vintage Air, the drier and the low pressure hose. I have heard of using Ester oil because of its compatibility with the mineral oil but have never run into a situation where I would use it. I am going out today and draining the old compressor's oil and will take a good look at it to see if there is any indication of contamination, if it looks good then I guess I drain the new compressor's oil and replace it with Ester oil and I should be good for vacuum and recharge. Sound OK or have I missed anything or any other area that should be addressed.

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That's exactly what did with my 134a conversion - except I'm still using all the factory A/C components in my 260Z. I replaced the receiver/dryer, flushed the system as much as possible, emptied as much of the mineral oil from the compressor as I could and replaced it with Ester oil. That was the spring of 2009. You'll see that I live in Arizona and daily drive Goldie to our shop and back. I've had to replace a compressor clutch in that period of time but everything else is still humming. (I've also been on a campaign to lower the heat infiltration into the cabin by improving seals and weatherstrip, better insulation on floors and trans tunnel, and mitigation of heat radiated from exhaust header, turbo, and downpipe. I now have a much more comfortable car in the 110 degree Phoenix heat.)

If you look way back on HybridZ you may find the scandalous pictures I took of my evaporator coil - getting temperatures below freezing... Yes, it is possible to have a cold coil and not have it become a huge block of ice (how does your refrigerator maintain a freezer section if the evap coil is 40 degrees? - it doesn't. How does it maintain a temp below freezing and not be a complete block of ice itself? cuz engineering...)

And, as I always say: Do the Kia blower upgrade for better airflow - and look for Lucas Hayhurst to start selling his improved dash ductwork piece - it improves airflow out the center massively while maintaining good flow to the side vents.

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3 hours ago, Cruzzar said:

Dave, I am replacing: the compressor, the condenser with a PF unit from Vintage Air, the drier and the low pressure hose. I have heard of using Ester oil because of its compatibility with the mineral oil but have never run into a situation where I would use it. I am going out today and draining the old compressor's oil and will take a good look at it to see if there is any indication of contamination, if it looks good then I guess I drain the new compressor's oil and replace it with Ester oil and I should be good for vacuum and recharge. Sound OK or have I missed anything or any other area that should be addressed.

sounds good. I would do a pressure check with nitrogen, look for leaks with soapy water. I think this is a better test than just checking for holding a vacuum, the system after all operates under pressure not a vacuum. But I suppose the vacuum method must be fine as that is what you generally read up on. I would let the vacuum pump run for at least 1 hour to make sure you get as much of the air molecules and boil of any water as possible.

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Just checked the old oil and it looks like clean engine oil. No evidence of oil breakdown or contaminates so I will drain the new compressor and reload with 6 oz. of Ester oil. I am still waiting for some fittings and will post when all is back in working order. Thanks for the tip on the Ester oil, I really didn't want to break the oil ring seal on the expansion valve.

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  • 5 weeks later...

Hi I just filled 6 Oz of Suniso 4GS and 0.9kg r-12. Compressor puls vacuum, so expansion valve is stuck closed. Will pump the r-12 back into a propane tank and try to clean the valve and the evaporator. If the valve is shot I will follow Dave wm' idea to use the valve as a manifold, or not quite, as i will make the manifold in the lathe, with internal treads for a generic valve. If the liquid copper pipe is too hard to make fit for the new valve I will consider to use a #6 hose with a 90 degree to the valve. 

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