I know there are some A/C techs on this forum so I'm gonna ask.

I'm swapping the A/C from a rust-bucket '89 4runner to my '84 pickup. The donor system had no pressure in it so I think I should assume that the parts I'm going to reuse, like the evap coil, need to be flushed. If I understand this right the expansion valve should not be flushed and should be replaced with new. I'll also replace the condenser, the drier/receiver and all the hoses/lines with new parts. What about the compressor? The donor vehicle had 160k miles on it. Is it possible to clean it out so I don't put any accumulated crud into my new expansion valve and other new parts? If so what kind and how much oil should go back in after? Or should I bite the bullet and get a new compressor as well? -- Matt

Flush with nitrogen and then place a vacum pump on the system and let it run for as long as possible. On large chillers if it will evacuate down to 400microns that is a pretty good target for all of the moisture to be out of the system. Some with automotive a/c experience may have a better target for this application. Nitrogen can be purchased from most welding and commercial gas outlets. The cylinder is connected to the system just like a refrig bottle via your guage hoses, and sent through the system and vented to atmosphere..

amen,you took the words out of my mouth

you cant be too dry or clean...in refrigeration systems...

From what I've read the are certain items that can't be flushed, like the drier, the compressor and the expansion valve. So it seems to my inexperienced mind like you'd be cleaning components and then assembling them. If I am cleanng out the components and assembling them afterwards it seems like it would be ok to flush with A/C solvent and regular compressor air. After assembly wouldn't subjecting the closed system to a high vacuum do away with the moisture from the compressed air, or is it just a bad idea to introduce any moisture in the first place? Where can I get a tank of nice dry nitrogen? Welding gas supplier? -- Matt

Check out this video of a low-buck A/C flushing rig and let us know what you think.

The kit looks like it would be better than not flushing at all. But I don't think it does anything more than what hooking up a nitrogen cylinder would do. Think of it this way. Technicians for my company flush $500,000 1000 ton centrigul chillers with old fashioned nitrogen cylinders, and they are cheaper than that kit at $270. The kit may work just fine, probably does, but having never used it , i cant say for sure. If it were me (just my 2 cents) I would clean and purge as much of the unassembled system components as possible then assemble the whole system, draw it down for 24 hours,break the vacum, then purge with nitrogen with a break in the system probably at the suction line of the compressor, reconnect then draw it down to 400 microns make sure it holds, draw it down..it creeps up...draw it down ...it creeps up etc...until you draw it down and it stays down if it does not eventually stay down it has a leak. Then you have it ready for refrig. Then the key is to have the system vacum draw whatever you want to put into the system into it. Opinions on this vary a great deal, the bottom line is that you have to get as much moisture and contaminates out as possible. Automotive systems are very robust and can stand alot more than some other systems. I know of one person that vacumed a system down for 3 hours, no flush, and have been running fine for years. Most commercial gas, HVAC shop, or welding supply can get you a tank if you decide thats the way you want to go....

I'm a real dummy on this issue so I've got to ask you to help me understand the purpose of the nitrogen. I understand using it to displace air, but how does it flush actual debris like compressor seal residue and sludgy oil out of the system? I've seen pictures of orfice tubes that are blocked with crud and vendors selling solvents for flushing and auto A/C guy swearing up and down that you've got to physically flush out debris <img src="/forums/images/graemlins/scared.gif" alt="" /> Does nitrogen do all that? Thanks for bearing with my ignorance. -- Matt

assemble your system ,If you feel the need to flush ,use refrigerant,just dont get caught venting it.A deep vacume is not a good leak check,it only proves you can hold atmospheric pres. (about 15 psi).Use nitrogen to leak check and blow it out.Run the vacume pump for an hour or so if you have a micron gauge use it go to 50-400 microns.DO NOT USE COMPRESSED AIR IN A REFRIGERATION SYSTEM.
You answered your own question about VENDORS WHO SELL FLUSH STUFF.A shoe salesman wants to sale shoes.before you go thru all the multiple evacuation stuff I would keep in mind that this is a 20 year old truck ,not the space shutle.All that stuff is my opinion ,this is not: the only thing you want in a refrigeration system is refrigerant and refrigerant oil,use nitrogen not comp. air cause it has no contaminates and the vacume pump can get it back out with no problems.There should be some kind of filter dryer to add to the system to help catch anything left in the system that could be removed and replaced if need be. ASE probly has some good guide lines for this on there web site ,if not I do I could e mail it .Good luck.

I totally agree w/CKTOY my multiple vac down procedure is a bit of overkill I was just living in the "I have nothing better to do than work on pulling down my refrig system" world. <img src="/forums/images/graemlins/notooth.gif" alt="" /> He is an actual HVAC technican were I am an office puke in the HVAC world. Nitrogen is used because it does not harm the enviroment, it is totally moisture free and can be dispensed under high pressure to blast the crap out of your system (like fiber in your diet), in the bad old days we just used refrigerant to purge. Many manufactures ship equipment with a nitrogen charge and technicians service refrigerant in during start-up.

nitrogen wont flush out sludge/debris.
this is what we do (usually this is a compressor failure, metal dispersed into the system)
1: recover any refrigerant then leak check with compressed air @ 150psi. yea you HVAC techs may disapprove but the system has metal throughout it and imminent failure of new parts is certain in any case.
2: flush system with liquid flush provided in the ac kit we bought , after removing failed parts
3: blow out with filtered/dried compressed air (getting water out is the key here)
3: install new/reman (with new o-rings/seals as needed ):
a: compressor
b: condenser
c: expansion valve/orifice tube
4:add oil as per service manual
5:vacuum down to 24" of mercury for 1 hour or more
6:recharge system, add ac dye for leak test.
7:check for leaks

this is an automotive ac system. it is not a critical system where serious bodily injury or death will result from using compressed air.
it is not meant to for things like food storage, it is for personal comfort (only one of my six vehicles have a/c; my wifes van. it regularly hits well over 100 in the summer here; i dont even have ac in the house)). all the ones i have done using the above have worked perfectly.

as far as the compressor goes, i would replace it. then go r134a (if its not in it already). we are talking about a 18 year old a/c unit.