AC system test....

[Chuck Leeper]

After discussing the repeated leak issues on a system, we decided that air pressure might be a better way. we decided after considering that there's always residual psi in the system, when it's off.
A couple interesting findings:
1. The vac test showed the system was tight. We then proceeded to add Freon.
The result was a massive leak. Was atuuactly found when testing the low psi side cycle switch. It should show continuity w/ the residual psi in a charged system. It was not, as the freon had leaked out overnight.
After repairs, resealed the compressor, we used the vac test, again. It held, so we then did a pressure test w/50psi...LEAK!
Repaired the leak. Pay CLOSE attention to the quality of the seals at the back of the compressor!!
The shop manual says 24# torque. That's for the old style compressor w/o the stepped o'ring bores, and the fat o'rings. This time, it was 24#, and then some!

2. The original low psi sw was supposed to drop out at about 35psi, w/ R12.
The replacement sw I have now checks at 21psi.

The test:
Hooked up an air supply, using an old charge hose. See the pic.
Hooked the VOM on ohms, to the 2 terminal spades on the sw.
Note the VOM is "OL"
Added 50psi thru the low side valve, captured it, by closing the valve.
The VOM now reads 0.0
I then bled the psi off slowly til the VOM went back to OL. Read the ga. 21psi.

Now, with the pressure back at 50, I shut the valve, and left it sit overnight. Stiil at 50, some 15 hrs later.
Am now doing the evacuation. Pump will run for an hr or so, to be sure the moisture is out. I'.

 

[aminga]

I've had that happen. My theory is that the vac sucks the seals closed.

 

[Chuck Leeper]

I've had that happen. My theory is that the vac sucks the seals closed.

Same thing my bud says. Strangely enuf, both tests held, when I did this last charge attempt.
Yesterday, I cleaned up the mess, installed the last set of seals I have, gold/green, and vac'd the system. Being the 134 has a propensity for migrating thru the older hoses, I'm wondering if this is why the air/vac works, but when 134 is the medium, it leaks??
28" held all day. Pressure test held 50+psi for several hrs.
There's a BIG diff in the red vs green seals as far as manifold fit. The gold/green, when torqued to 25#/, produced a very consistent air gap at the manifold/comp joint. Waaay off w/ the red/gold.
Going to put can # 11 in today!
Found the 134 to be getting expensive..Most local ap stores are near $10/can....Wally World came thru! $4.79.

 

[TR Custom Parts]

I was told by my HVAC guy at work to always pressure test with nitrogen.

 

[earlbrown]

I was going to mention using something like nitrogen. My theory was that it would mix with the air and when you blew off the pressure (giggidy), it would take some moisture out with it (giggidy).

 

[aminga]

I have a leak where the hard line is swaged on the rubber line over the radiator. But it only leaks when you press on it so far it's held refrigerant for 3 years