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How to get DRY shop air for purging after flushing

scusack71 on Tue August 11, 2009 12:46 PM User is offline

Year: 1998
Make: Dodge
Model: Intrepid
Engine Size: 3.2
Refrigerant Type: R134a
Ambient Temp: 77
Country of Origin: United States

I performed a flush on my a/c system with my new HECAT Pulsator. It works awesome as advertised!

My issue is that I have been trying to purge the evaporator and condenser with dry shop air for minimum 30-40mins each and then perform the "air burst" clean/dry test. My purge system has resulted in:

1. my 5hp, 25 gallon air compressor connected to

2. 6-foot air hose connected to

3. a small inline water/oil separater filter going into

4. a small (100psi max) inline descicant dryer filter which goes into

5. an commercial regulator/filter connected to

6. a fifty foot hose (I know... alot of pressure drop) with my air nozzle

...and I still get water from my rubber air tipped blower when I try the high burst (old school) dry test.

I can't afford a refrigerated dryer and I'd still be investing some $ trying to make a water separating coil contraption. The humidity here in Michigan is fairly high (75-85% now) and compressed air brings out much of the water. Hell... my desicant turned pink after just a short period. Should I buy one of those 36" desicant dryer tubes from Harbor freight. I believe I can get one for $32 and the manual says you can change the desicant every 6mos or so. I don't know if I can trust that coming from harbor freight. Any tips from the wise is greatly appreciated. Thank you.

Matt L on Tue August 11, 2009 3:24 PM User is offline

NAPA sells a desiccant dryer with a replaceable element that is higher capacity, but also a substantially higher price. I believe that it is designed for painting, which should be pretty good for AC work, as long as you can get enough CFM out of it.

HECAT on Tue August 11, 2009 4:12 PM User is offline

Thanks for the update that the HECAT Pulsator Flush Gun works as advertised. I am also happy to see that the air purge and verification processes as outlined in the instructions are being followed. It can at times, be difficult.

You have good sized compressor (5 HP) and may just be asking too much of the "small" (port size?) separator and dryer. The hot air may just be quickly passing through these units and condensing in the 50 ft hose as it cools.

One (crazy) thought to try and make the "small" units work, would be to move the separator and filter closer to the work end of the hose; after the regulator and taking advantage of the "drop".

Also make sure the separator is plumbed properly as it will only work one way; and be sure the storage tank is drained (regularly) of any condensate buildups, and your air line is coming off that tank at a high point.


HECAT: You support the Forum when you consider for your a/c parts.


scusack71 on Wed August 12, 2009 10:27 AM User is offline

Thank you for the tips. I will rearrange my air lines and separators.

All my port sizes are 1/4" NPT. But maybe your right about the rush of air condensing in the 50' hose. I only noticed the condensate when blasting a burst during the verification, which I thought was defeating my purpose of getting it out. My compressor is a craftsman (horizontal style) and has the line port high. I need to be more diligent with draining the tank though.

I'll give it a shot and see how it goes. Thanks again for all the help and just to let anyone know that the Pulsator is a great tool and I did have some descent debris but only fine aluminum particles and it flushed out all the dyed oil. I'm just anxious to get the system fresh and cleaned out for assembly.

Matt L on Wed August 12, 2009 1:11 PM User is offline

Completely agree on the Pulsator, it's a great tool. I'm glad that I bought it before the latest price increase, but I would buy one again in a heartbeat if I hadn't.

I also put the conventional water separator at the end of the hose, and should have suggested it, but it still wasn't perfect. I guess nothing will be quite perfect when you're talking about that much airflow.

NickD on Wed August 12, 2009 3:28 PM User is offline

Found a leaf blower jury rigged to a hose does a far better job than an air compressor for blowing out components. Accumulator or receiver is the last part to be installed. Could rent a tank of liquid nitrogen for a very dry air source, feel that is going overboard, that is why we have a vacuum pump and taking a nap while it's running to get the last bit of moisture out. Could also move to the dessert.

scusack71 on Thu August 13, 2009 7:13 AM User is offline

I would like to get it fairly dry. Like I said, it seems to feel fairly dry while purging with a nice steady flow, but I can't really verify how dry it is (H2O vapor molecules are tiny), especially with Michigan's August humidity. And I seem to get condenced water while giving it a pressure burst of air while doing the "verification test" HECAT has outlined in their procedure. I personally would feel more confident with a refrigerated dryer or nitrogen. The dryer would be a bit more costly compared to the less expensive inline units that can be installed on the supply setup. But even a small used refrigerated dryer may be reasonable if you have other dry air needs other than purging your a/c system (painting, air tools, etc). ...and I'm not sure how much it costs for renting an N2 bottle. I can get a regulator for a descent price through my employer (but still not cheap), but even though N2 is fairly cheap, I'm not sure as to how much the hastle it is with getting a bottle (i.e. account setup with vendor, pick-up/return, etc), but it is 100% gaurenteed to be dry!

Also, as NickD mentioned about kicking back and letting the vacuum do the work after a good purge, I am all for it... but from what I read from HECAT (I believe it was HECAT) that it's not good to rely on the vacuum as means to pull all the water out as a result after a flush/purge, since a bad purge can leave some liquid or droplets in the system. They like the old school verification test (I believe it is explained in the flushing procedure written in the forum by HECAT). Especially since that ANY water (moisture) mixing with the oil could cause catastrophic damage. Personally, I have a fully fresh system including my compressor and hope to have a successful assembly and charge the first time after assembly. That is my only reason why I would want a fairly decent sanity check that all the water is gone, "leaving none behind." I know, I'm a worry wart.

Oh well, I really appreciate everyones feedback and ideas. It has been very helpful.

Edited: Thu August 13, 2009 at 7:20 AM by scusack71

HECAT on Thu August 13, 2009 12:44 PM User is offline

Originally posted by: scusack71
I know, I'm a worry wart.

I would say cautious and conscientious.

HECAT recommends dry air for 2 reasons. (1) We don't want moisture introduced to the air operated tool (flusher), which could establish corrosion issues within. (2) It is not good to introduce excessive moisture to the A/C system.

HECAT recommends air purging to remove the solvent over vacuum because the evaporating solvents would mix with and contaminate the vacuum pump oil; requiring excessive oil changes, or potentially a vacuum pump failure.

HECAT recommends the air "Pop" as a verification process for 2 reasons. (1) Too many variables in component designs and system failures exist. (2) We want YOU to be satisfied and comfortable in confirming your own work, before sealing up the system.

With all that said; you will end up with some solvent trace residues, moisture from atmosphere, and possible moisture introduced from your blow gun. However, all this can be remove with the vacuum process and it would be wise to extend the vacuum process to account for this; take a nap, as Nick says. Monitor the vacuum pump oil for clarity and if it becomes cloudy; change it.


HECAT: You support the Forum when you consider for your a/c parts.


scusack71 on Fri August 14, 2009 12:29 PM User is offline

Thank you again for your input. I really appreciate it. However, I do have another question:

I have a Vortex A/C Recovery System I picked up on craigs. I was wondering if I should get a separate vacuum pump (i'm not sure what cfm) to draw down for leak checking and servicing or is my vortex ok to use for drawing the vac after a flush/purge? The vacuum pressure is good, but since I did a flush, you mentioned chemical residue and water in reference to contamination of the vacuum pump. Since the vac system recovers, I didn't know if I was suseptible to any contamination that could get into my unit and 134a container, etc. I belive the pump is lubeless. Thanks

HECAT on Sat August 15, 2009 6:19 AM User is offline

I am not an expert on the various recovery tools. But as I see it, you will need a separate vacuum pump. The mini recovery systems appear to be just that. They use the oil-less compressor that will pull a light vacuum as part of the refrigerant recovery process and the discharge goes to the recover tank. I don't believe you would use this tool for a final vacuum of the system. Maybe someone else more familiar with such unit can add confirmation (?).


HECAT: You support the Forum when you consider for your a/c parts.


NickD on Sat August 15, 2009 6:38 AM User is offline

Would recommend a dual stage vacuum pump, capacity in a MVAC system isn't exactly like an HVAC used in a skycraper, only about a quart of so, so pull down is very quick, look for a pump with a very low micron rating. Micron is a unit of measurement for distance, one millionth of a meter, so it's actually microns of mercury or Hg. Like a pump with a rating of less than 50um/Hg. That is the specification they should give, just saying microns means nothing.

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