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Guest Message by DevFuse

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A/C Expansion Valve and Weird Gunk

A/C Air conditioning expansion valve txv

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5 replies to this topic

#1 PlaneDriver


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Posted 12 September 2013 - 09:12 PM

I am slowly going about converting my '89 RX from R12 to R134a because the pulley bearing on my original compressor failed. I removed the evaporator today and took it apart to get the expansion valve out. The first thing I noticed was some weird rubber/tar gunk around one connection of the expansion valve and around where a piece of it touches a coolant line. What is this stuff? Is it necessary? I hope it wasn't put on to contain a leak. It wasn't tight on the parts so I don't think it was to fix a leak. The pictures below show what it looked like. I took the pictures after I peeled it off so it is just laying there as a representation in the pics.



The new expansion valve I bought from RockAuto has different thread sizes than the original so it won't fit. It also won't fit over the pipes to seat against the O-ring. I will have to return it. It also has a third connector coming out of the top. I found this thread that says this was a feature of Hitachi A/C systems, but mine is Panasonic. 



I was going to get together with a local Subaru group on Saturday to work on this but I don't think I can get a new expansion valve by then. My thought is to use new O-rings and reuse the original expansion valve. It seems people frequently do this when switching to R134a from R12 with no adverse effects and I never noticed anything to think my original had problems.


Thoughts on the weird gunk and reusing the expansion valve?

#2 MR_Loyale


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Posted 13 September 2013 - 02:33 AM

Honestly I switched mine over this year and never went to all this bother. The conversion kit I got at Walmart had esther oils in it which are compatible with the R12 oils already in there. Has been running all summer long with no problems. Kit even came with a CD.

#3 ehartshorn



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Posted 13 September 2013 - 11:47 AM

That tar like substance is on every AC system I've ever worked on.  I think it is to reduce harmonic vibrations/pulses in the system, but that's my own guess.  It's been 25 years since I held an AC certification and I honestly don't remember if I ever knew what it was...

#4 MR_Loyale


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Posted 13 September 2013 - 10:04 PM

A/C insulating tape, called Prestite:




Doesn't look that awful when it is initially put on there. Its insulation and a moisture barrier.



#5 NorthWet


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Posted 14 September 2013 - 10:31 AM

The "gunk" is mostly to allow the frigid gas to reach the evaporator without picking up stray heat between the expansion valve and the evaporator.  Concurrently, it prevents water from condensing on the otherwise exposed cold piping and being a nuisance.

#6 presslab


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Posted 29 June 2014 - 01:02 PM

I thought I'd bump this thread to see if you could help me with a couple questions.  How hard was it to remove the evaporator/expansion valve?  Can I get to it under the dash?  Did you end up finding the right part and if so what was the part number?



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