Using a bicycle pump to find AC leaks.

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Apr 7, 2010
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Miami
I have a substantial leak in my 2001 Honda Civic. I though it was the service port valves, since when I undid the service port plastic caps, some gas hissed out of them. I ended up replacing a pipe, because new valves were still hissing in the pipes. I suspect corrosion did them in. With the new pipe, there is no more hissing.

Pulling a vacuum showed a gradual leak to ambient pressure in about 30 minutes. That is too large a leak. I know conventional leak detection is pumping refrigerant into the lines with perhaps a dye leak detector or chemical sniffer. I have found neither of those methods as accurate or successful as I’d like them to be. I also am uncomfortable with using expensive and environmentally harmful Chemicals as a leak detection tool. R134a prices have also shot up. It was $17 for a small can.

Vacuum isn’t so great for determining where the leaks are - pressure is. I don’t own an air compressor, but I thought, what about using my simple and effective bicycle pump? I use that manual push pump for inflating my car tires to 40psi. Perhaps I can pressurize the AC lines and use the soap and bubble method to fine leaks.

I have already sourced a shrader valve to NPT 1/4” on Amazon. It’s only $8. I can use an adapter from NPT to get to gauge set threads. Then it’s just a matter of pumping air in until I get 40 or so psi, and spray all over the system to find leaks.

Anyone ever heard of this? I will post pictures on Friday, when I plan to do this.
 
Seems smart to me. Don't let it sit a long time without being vacuumed. I suppose with moisture it it, some parts could start to corrode.
 
I have read that moisture is a problem with compressed air, but the system is empty now, so there must be moisture in there already.

nitrogen requires a cylinder and those cylinders are expensive. I would also need a pressure regulator which is $40 for a cheap one.

Would it be worth getting a small 20 cubic foot nitrogen cylinder? I rarely do AC work. Do those cylinders last decades?

I don’t want perfection, just pinpointing a significant leak on the civic.
 
Any air pump or compressor will introduce moisture into the system-the receiver/dryer can handle a little, but I wouldn't (& don't) chance it. Newer automotive PAG refrigeration oils are extremely hygroscopic, very easy to contaminate with water as well.
 
Most shops use shop air to pressure test one. But you need a filter to remove moisture. Don't just pump it up with your pump with all that moisture in the air.
What are these filters called? Are they easy to attach? I prefer this to owning an explosive nitrogen cylinder.
 
I think if you run the vacuum long enough once you fix the system, you won't have to worry about moisture in the oil. I can't see the oil holding onto any water if you keep that pump running for 30 minutes or so, should boil it out. Unless your pump can't pull a strong vacuum I wouldn't worry.
 
It’s SOP in commercial HVAC to keep nitrogen around to purge lines. Nitrogen is a relatively “dry” gas as it comes from the cylinder, much like breathable air from a scuba/SCBA tank(which BTW, there’s adapters to connect the low-pressure 3/8” QC on a scuba set for the BCD to 1/4” NPT). Your approach is fine, just pull a vacuum for long as possible after you’re done, ideally the drier should be replaced after repairs are made, oil added to restore the lost amount and system evacuated/charged.
 
Sorry if I missed it, but are you trying to fix the leak yourself and then have a shop pull a vacuum on the system and then re-charge it?

If it's got to go to a shop anyway, I'm not sure of what your going to save cost wise by DIY.

Like said, pulling a vacuum on the system should vaporize and evacuate any moisture that's in the system.
 
nitrogen requires a cylinder and those cylinders are expensive. I would also need a pressure regulator which is $40 for a cheap one.

Would it be worth getting a small 20 cubic foot nitrogen cylinder? I rarely do AC work. Do those cylinders last decades?

I think some places will rent the cylinder to you, and possibly the pressure regulator too.
 
Like said, pulling a vacuum on the system should vaporize and evacuate any moisture that's in the system.
Most shops don't vacuum long enough. The robinair units most shops have are factory set for 15 minutes. Any longer and they burn up!

Maybe he can find a shop with a different machine or a portable vacuum pump that they can leave running while they go to lunch?
 
I have a fancy made in US vintage vacuum pump that can run for an hour with no problem.
 
Air from a hand pump or air compressor adds moisture into the system. Does it work with soap bubbles yes. Does it contaminate yes. A triple evacuation would be recommended. Dump the air pull a vacuum break the vacuum with nitrogen repeat twice more weigh in charge.
 
AutoZone and some O’Reillys rent vacuum pumps, FYI. You can also buy one for $150ish from Harbor Fright. It won’t be an Robinair or a Yellow Jacket not will it pull above 200 microns but it will do the job.
 
I would fill it up with r134a at five dollars a can from walmart dot com and add some dye. The leak you are describing sounds pretty big to me.

Or take it to a shop if you are environmentally sensitive.
 
I think everyone’s favorite purveyor of Chinese tools(Harbor Freight) also sells leak detectors as well. It may be worth adding a wisp of R-134a(which is getting more expensive by the day, CA charges $10 for a refundable deposit) and using one of those for places for you can’t see.
 
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