How can I pressure test the A/C system?

Posted By: feets

How can I pressure test the A/C system? - 05/01/12 03:53 AM

I don't have an A/C machine at home but I do have a set of gauges.
How can I pressure test the A/C system at home without buying lots of cans of A/C dye?

I was playing with the Imperial tonight. I flushed the heater core with water and it leaks. Yay. Finding another one will be fun.
Just for giggles, I pulled the cap off the A/C schrader valve. There was a bit of residual pressure in the system. Not much mind you, but there was positive pressure.
I spun the clutch by hand and the compressor seems to turn smoothly. I can't feel any appreciable resistance but there's hardly any pressure in the system.
I fired up the engine and jumped the compressor clutch. It kicked in without any bad sounds. There was no change in idle speed but I wouldn't expect that after turning it by hand.

I'd like to push my dumb luck and see if the mechanical bits of the system will work.

What's the best way to pressure test it at home?

Posted By: zrxkawboy

Re: How can I pressure test the A/C system? - 05/01/12 04:04 AM

The best way I know of is to pull a vacuum and see if it holds. Do you have access to a vacuum pump?

As far as the heater core, when mine started leaking in my 57 Plymouth, I had it re-cored locally.

Posted By: finadk

Re: How can I pressure test the A/C system? - 05/01/12 04:14 AM

I have never seen an AC system pressure tested. Instead they are evacuated using a vacuum pump. I bought a cheap one from harbor freight that operates off of a shop air compressor. You such all the air out and make sure it holds the vacuum.
Remember r12 freon is very very expensive, you may want to retrofit to r134a, but the oils used in r12 and r134a are not compatible so while the system is empty you may want to take the opportunity to flush it and get it ready for the r134a.

Posted By: 68HemiB

Re: How can I pressure test the A/C system? - 05/01/12 04:16 AM

Another vote for a vac test (although a system that will hold vacuum isn't necessarily guaranteed to hold pressure).

At the risk of stating the obvious, you don't have to spend the $$ on R-12 to see if holds pressure. Armed with an adapter, you can use much cheaper -134a for pressure testing. Truth be told, you can even RUN R-134a in your system...

Posted By: OzHemi

Re: How can I pressure test the A/C system? - 05/01/12 04:17 AM

Quote:

Another vote for a vac test...

\

If only he had someone local to borrow a vac pump from....

Posted By: feets

Re: How can I pressure test the A/C system? - 05/01/12 04:21 AM

I know about vacuum testing the systems. I've done that on my truck and Concorde.
I was hoping to pressure test the system so I could find any leaks without going through a dozen cans of Freeze 12 with dye.

I'd have more time to mess with it at home during the week. I'm the late guy at work and only have an hour or so after work before they want to lock the facility down for the night.

Posted By: OzHemi

Re: How can I pressure test the A/C system? - 05/01/12 04:23 AM

What about the 134 idea of etevS then?

Posted By: herkamer

Re: How can I pressure test the A/C system? - 05/01/12 04:23 AM

Vacuum isn't very accurate esp with the HF pump. Dry nitrogen is the way to test with a true pressure of what the system would run. 134 is great if you want cancer...

Posted By: finadk

Re: How can I pressure test the A/C system? - 05/01/12 04:28 AM

I never heard the 134a cancer link, but heck as long as it does not hurt the environment who cares how many PEOPLE it kills.

Posted By: 68HemiB

Re: How can I pressure test the A/C system? - 05/01/12 04:33 AM

Quote:

134 is great if you want cancer...

For the record, I do not recommend that you smoke R-134a in your bong...

Posted By: elitecustombody

Re: How can I pressure test the A/C system? - 05/01/12 06:31 AM

Quote:

Vacuum isn't very accurate esp with the HF pump. Dry nitrogen is the way to test with a true pressure of what the system would run. 134 is great if you want cancer...

Am I missing something? As long as OP has good gauges that's all that matters if he can manage to pull vacuum.

BTW,OP , the HF little red plastic box/pump works just fine for quick vacuum ,as long as you have air supply to operate it. I use it all the time.

Posted By: herkamer

Re: How can I pressure test the A/C system? - 05/01/12 10:42 AM

Quote:

I know about vacuum testing the systems. I've done that on my truck and Concorde.
I was hoping to pressure test the system so I could find any leaks without going through a dozen cans of Freeze 12 with dye.

Don't think the question was about the HF vacuum pump. It is fine for a shallow vacuum, but don't expect results like using a real vacuum pump. It works great for the refrigerant that I use because it doesn't require a deep vacuum.

Posted By: therocks

Re: How can I pressure test the A/C system? - 05/01/12 11:05 AM

Ive done AC since the 80s.You pull a vacuum and let it set.See if it drops.Then you add a small charge and use either a black light or leak detector.I prefer the light as the dye is easy to see.If you have a leak you usually reclaim the 134 you put in.We did have a 12 machine at work but it hadnt been used in 5 years.I might have a heater core.I cant remember if I scraped the heater setups from my 70 Imps.Rocky

Posted By: GoodysGotaCuda

Re: How can I pressure test the A/C system? - 05/01/12 12:19 PM

Dye is one of the best methods to get that done, you can try one of those little electric sniffers..however I've never had any luck with those. You can breathe on it and set it off.

Posted By: 340SHORTY

Re: How can I pressure test the A/C system? - 05/01/12 06:12 PM

when you turned it over by hand did you have the power on and the clutch was engaged or was it just freewheeling the bearing? .
if the system is low you cant energize the clutch therefor lock the clutch/pully and be able to turn the pump.

Posted By: Challenger 1

Re: How can I pressure test the A/C system? - 05/01/12 06:19 PM

Those sniffers are very senitive and the tip can be ruined/tainted real easy. Never stick it into the hoses or touch anything with them.
If freon get's on it most times they need to be replaced, the sniffer tips.

AC sucks to work on without a recovery machine. I have been busy with AC repairs here lately. I am working on AC as I type this.
Most of my trucks lose about a 1/2 pound per year.

I just pull it all out, pull a vacuum and recharge with 2.2 pounds and reset the dash light. Good for another year until I find it 1/2 pound low next spring.

Never any leakage visable around any connections or hoses.

Posted By: 1970Dart3406

Re: How can I pressure test the A/C system? - 05/01/12 06:37 PM

You would be better off pressure testing the system as well as vacuum testing. Your system may not leak under a vacuum, but under pressure it may. Under vacuum, the seals or O-rings will move in one direction and under pressure they will move in the other direction. This can and does happen. If you are able to, put a gauge on the low or high side port and then pressurize from the opposite port. Watch the gauge for 20-30 minutes to see if you have a pressure decay. That's my suggestion. It's based upon my experience as an engineer at one of the OEM manufacturers. In the recent past I spent several years working on the repair of HVAC systems on new units at the factory. We pressure tested all leakers with helium before evac'ing and refilling.
Just my 2 cents..............

Posted By: feets

Re: How can I pressure test the A/C system? - 05/01/12 09:33 PM

Quote:

You would be better off pressure testing the system as well as vacuum testing. Your system may not leak under a vacuum, but under pressure it may. Under vacuum, the seals or O-rings will move in one direction and under pressure they will move in the other direction.

That's why I want to pressure test it.
One of my techs has a vacuum pump he'll let me use. The guys are all for evacing the system and recharging.

I know how compressor clutches work. I spun the clutch, not the pulley. The pullies obviously spin freely because I've been driving the car with the A/C belt on.

Posted By: 340SIX

Re: How can I pressure test the A/C system? - 08/10/20 05:09 AM

Originally Posted by finadk

That is what j do the Red Cheap HF Box.
My buddy who does home A/C has a,pump and does same thing. Sucks the system d own and leaves goes on another call and returns to see if it is ok to fill or not.

Posted By: Twostick

Re: How can I pressure test the A/C system? - 08/10/20 06:05 AM

The fact that it has ANY pressure in it at all tells you it's sound. If it had a leak any bigger than what will get past the crank seal naturally over many years, it would have had zero pressure.

If it's still running R12, see if you can find some and just charge it back up. I would avoid those R12 drop in replacements if I could as my understanding is they are probably propane or similar.

If it has been previously converted to R134 then off to Walmart for a few cans.

Kevin

Posted By: mopardad

Re: How can I pressure test the A/C system? - 08/10/20 11:19 AM

you can use nitrogen

Posted By: Jim_Lusk

Re: How can I pressure test the A/C system? - 08/10/20 08:03 PM

You can pressure test with shop air (needs to be vacuumed longer and best if the air is VERY DRY). I made up a set of fittings to connect to one hose on the manifold set with a ball valve to shut it off. Vacuum will not necessarily show all leaks as stated above.

Posted By: 360view

Re: How can I pressure test the A/C system? - 08/10/20 10:59 PM

As others have posted above,
Dry Nitrogen is the conventional Way to pressure test, and the EPA states in writing that “small amounts” of Freon can be added to the nitrogen gas for leak testing.

If it is an old R-12 system, some pressure test with
Difluoroethane, the relatively cheap gas in some “Dust-Off” or “Canned Air” spray cans.

In the AC world Difluoroethane is known also as HFC-152A
It is flamable.

You need to buy a “Can Tap” to transfer the gas from the Dust-Off cans through a hose to AC systems.

Some R-12 system conversion details using HFC-152A are here:

https://www.s10forum.com/threads/how-to-r152a-conversion.493953/

Posted By: ruderunner

Re: How can I pressure test the A/C system? - 08/14/20 09:43 AM

Feets, how long since the last charge? If it still has pressure after 10 years you should be fine.

I've also used shop air.

Posted By: Kern Dog

Re: How can I pressure test the A/C system? - 08/16/20 02:24 AM

Well, since this topic was started in 2012, lots of things may have changed!

Posted By: njmopar

Re: How can I pressure test the A/C system? - 08/16/20 01:09 PM

Best way to test is to pressure test with a nitrogen/hydrogen mix. They will charge the system at about 200 psi and then use a sniffer which will detect the hydrogen leaking from any seal or fitting. Sniffer will indicate the level of leak in a gram or ounce per year scale. Vacuum alone will not be accurate, shop air is just adding moisture and there is no way to sniff for leaks. If you want to keep R12 or not waste R134 which is getting more expensive, find a shop that has this setup. Save yourself future depression and find and fix the leaks now.