griffiths

Expansion valve and its orings tend to leak before an evap. Its possible that is the source of the leak pulled I to the vent.
A dye test is only going to show what you can see, if the exp vale is visible do it

Ducman82

Dye it and run it. Cheapest route you can go. Pulling the dash is not an impossible job, just a little time consuming and finicky. I have done it plenty of times.

worf928

100% agreement. It is a lot of work to get to the evaporator and even more work to put everything back they way it should be, working, not leaking etc. It's easily a 16+ hour job.

Also when the dash is out, you should replace the diaphragms in the three vacuum actuators that are under there. (Recirc vent is a fourth but you don't need the console out to replace it; not much common labor.)

bureau13

Fwiw the expansion valve and o-rings are new...

dr bob

Yes, but...

There are more than a few cases where an o-ring at the expansion valve is scuffed on installation. You get to line up the two pipes from the evaporator, and you have to get it just right to avoid scuffing the o-rings. More than a few people decide not to lift the clamps at the fuel cooler when they change the expansion valve; instead they just pry it back away from the firewall. So another misalignment, 'solved' by tightening the clamps around the fittings more.

When you have a leak at the expansion valve, the vapors pool in the evaporator housing, giving a misleading reading when the sniffer is in the vent.

I don't have a horse in your race, but I'd wager a nickel that the evaporator isn't leaking. Meanwhile, the expansion valve is exposed enough to give it the soapy water spray and look for bubbles treatment. Four connections to check, all conveniently grouped together for your testing pleasure.

worf928

What DrBob said.

Also, I always sniff the evaporator with no fan running so that my sniffer isn't fooled. There's no need to have the fan running. If the evaporator is leaking it will fill up the heater core with refrigerant so you don't need anything to 'move' it to the sniffer.

If the sniffer doesn't pickup anything under the front expansion valve, but does pick up something in the vents then it is more likely that evaporator is leaking.

However, as others have posted: if the leak isn't too big and if it's r134 leaking (as opposed to precious r-12) then filling it once a year is a cost-effective approach.

BUT, make sure to add a bit of the correct refrigerant oil with each dose of r-134. If the system is leaking gas it is also going to leak oil. Eventually, filling just with gas will lead to no oil in the system, a seized compressor and a big, big mess.

bureau13

I can attest to those expansion valve issues. This is actually the second new one, after I butchered the first. I could certainly believe I may have messed up an o ring on reinstall. I definitely should have had him show me a sniffer test at the expansion valve...

dr bob

Since there is pressure in the system now, some liquid diswashing soap in water goes into a spray bottle, and you get to spray the connections at the expansion valve looking for bubbles. Simple, and you don't need a sniffer. Just your eyes and a small inspection mirror to see bubbles all the way around the connections.

bureau13

Wow...that's so obvious and easy I had dismissed it lol. I guess I was thinking leaks of this nature (after 2 hours, vacuum went from 30 in-Hg to 20) would be too small to show up that way. I will certainly try this before I do anything else!

dr bob

I ASSumed that you have refrigerant pressure in the system already. No pressure means no bubbles at leaks.

bureau13

There is some...enough for them to leak test it. It's "holding" some positive pressure, but probably not enough. I'm having the rubber hoses rebuilt and fixing that primary leak, converting to R-134a (gave up the R-12 fight lol) and I'm gonna run it, and see what happens. I'll definitely test that area by the expansion valve as you suggested when that's complete.

dr bob

Do the testing with a little nitrogen before you charge the system with refrigerant. Find/fix leaks then.

bureau13

OK, an update here. The shop rebuilt the hoses, then found a leak which they initially thought was the compressor. It turned out the compressor was fine, but one of the fittings must have come loose as I wrestled it into position so they tightened that up. They still maintain that there is a leak at the evaporator, but filled it up, put in some dye and it worked great...for just under a week. I noticed it not cooling as well, so I got out the UV light and started looking for evidence. I saw no dye on the driveway from evaporator condensation...not sure if I would realistically expect to? I saw no dye at the evaporator/expansion valve junction. The only place I did see it, was at the R-134a low pressure retrofit valve that they installed. Under the cap, it was also quite oily. Now, you get a momentary burst of escaping gas when you connect/disconnect from that, so I can't say for sure that wasn't the issue, but the retrofit valve was on an elbow...and was easily hand-turnable on the threads. That seems way too loose. I topped it up and tightened it about a half turn...which puts it in a completely unusable position, naturally. Here's my question (finally!): How tight can I turn that safely? Since it's an elbow, it's pretty easy to hand-crank that thing tight...I might be able to get it all the way around and back into a useful position...but I do NOT want to strip the threads on the car end. That would suck. What's safe here, anyone know?

Ducman82

why did they add an elbow? i can't see that being any help on the low side..

bureau13

I don't know, but I hated that stock low side spot though...I always had trouble getting my gauges to thread on. The elbow definitely seems to make it easier.