AC vacuum frustration

[Shran]

I needed to replace the AC condenser in my Explorer and while it was apart I also replaced the accumulator, both lines, the orifice tube and all the O rings. I reused the compressor and the evap core.

Last night I pulled a vacuum on it. I was able to vacuum down to about 10hg on the low side and something below 0 on the high side (my gauge just goes lower than 0 with no marks there.) Not good, I have a 7cfm vacuum pump and it'll pull 30hg on a car pretty quick. I shut the valves and left it overnight and it held.

This morning I went out and messed with it some more. I found a damaged seal on the yellow hose, the end that connects to the pump. Bingo... just about 30hg on the low side and touching the stop on high after about 30 minutes. So I closed the valves... and lost all vacuum in about a minute.

What gives? I didn't touch anything other than the seal on the center hose. I don't understand why suddenly it's not holding when it held last night... do my gauges just suck, they are cheapos? Additional vacuum making something leak?

 

[Uncle Gump]

So you isolated the gauges after pulling it down?

Gauge hoses even with the gauges isolated will certainly leak with no less then 4 failure points.

Leaks are tough to find without there being working pressure in the system.

 

[Shran]

I'll have to mess with the hoses and see if I can narrow it down a bit. I might go buy a small nitrogen cylinder and pressure test it with that... I already have a regulator for that and it'll come in handy in the future.

Just weird and hoping I don't have to replace the evap core... Not one of my favorite parts to replace!

 

[RobbieD]

As a next step I'd try to beg, borrow or rent another gauge set, as "known good" as possible. A set of old janky gauges could very well be your leak, and if it were me I'd just feel better about troubleshooting a system leak if two sets of gauges both show a leak-down.

If you do end up pressurizing the system with nitrogen, soapy water can show the leaks (just like for a tire). When I installed AC about a hundred years ago, the occasional leaker was usually a displaced or damaged o-ring, and rarely a bad new component. These days it could more easily be a bad new replacement component.

 

[Eddo Rogue]

maybe your schraeder valves are bad or need o rings?

 

[Shran]

I scored a nitrogen cylinder from the pawn shop today for 75 bucks. Had enough left in it to do a short leak test... I put 200psi in the high side and could hear it leaking out of the pressure switch on the accumulator. Weird spot to leak but maybe I damaged the o-ring there. Going to fix that, refill my nitrogen and try again.

 

[Eddo Rogue]

That's an awesome pawn shop to have such a thing.

 

[Shran]

Pretty sure I narrowed it down to a gauge problem... I picked up a new set of gauges and it held steady at 130psi for 48 hours.

Pressure switch on the accumulator still leaks. I removed it to leak test the rest and ordered a NOS Ford part to replace it.

Note to self, original gauges worked fine before loaning out... Those will be my loaner gauges from now on...

 

[Eddo Rogue]

This is why I have 2 sets of gauges, and 2 torque wrenches, and 2 shipping scales, and 2 printers....so on and so forth. Thanks technology, for nothing.

 

[Shran]

Well...frick. I obtained the NOS Motorcraft pressure switch and that fixed the obvious leak there. I put 120psi of nitrogen in the system and it dropped maybe 4 or 5 pounds overnight (was almost 70 degrees when I filled it, 45 degrees this evening when I checked) so I figured the temperature differential caused that. Pulled a vacuum on it for 30 minutes, best I could get out of that was about 16/17 in/hg and it lost all vacuum within 30 seconds of shutting the pump down.

I guess I will blow it full of nitrogen again and do another soapy water check. This is irritating.

 

[Uncle Gump]

That is irritating...

I get to do this very thing on the G-Unit this spring. Cause it's gonna have A/C.

 

[Eddo Rogue]

I've done my AC a few times. My HVAC buddy does the refrigerant part. it blew cold for half a summer until the compressor gave out again. Now it works, but the air blow luke cool, not ice cold. Will probably do it again this spring, but this time change everything.

 

[Shran]

I feel like I've probably got a bad O ring somewhere. In my mind holding pressure but not vacuum would indicate a seal is pushed out and working under pressure but gets sucked in and creates a leak under vacuum.

The O rings that come with new AC parts are terrible. The ones on my new condenser were so loose that they were almost falling off. I always buy O ring kits whenever I'm doing this... I end up using most of them to replace other "new" ones.

 

[Shran]

Been screwing around with this on and off for the last few weeks... still cannot get it to hold vacuum. I tightened fittings on the evap core and it maybe made it a little better, replaced every O ring, now it's worse and I can't pull much of a vacuum at all. I'm going to try a new evap core, really did not want to go that route but I've only been messing with it, and now my leak is worse... I feel like a combination of age and me messing with it has damaged it somehow.

 

[superj]

that is a bummer. hopefully one last new part and you will be good