burncycle2000

I got in a small fender bender about 3 years ago and it did some slight damage to the front end of my 95 tacoma. After I replaced the dryer the metal AC lines and even the condencer for good measure I had the system checked with dye and didnt see any leaks. The system did not hold coolent.
I dealt with the heat and year two comes around and I take my truck to an AC shop. We realized that the shredar valve ( I hope I spell it right) was faulty. Everytime we would charge the system the pressure or something would push the valve stem in and would suck it down so hard ruining the spring so the stem would not pop back up, and would leak coolent. We went through 3 shreder valves and even replaced the hose and connecter for the low side.
Year 3 comes around and about a month ago I took the truck up to one of the major Toyota dealships in Atlanta thinking they have to know. The guy was cool enough to check it out for free, but spent half the time trying to figure out why my compresser wouldnt kick on. After 45 min of looking I got into the truck and pressed in the AC button which kicked on the compressor needles to say I was not impressed. He was so tired of looking at the truck by that point that we never got into what I was trying to tell him and the day was wasted.
So its getting hot again here in GA and Im at wits end trying to figure out what is causing my system to ruin shreder valves and leak coolent. PLEASE HELP ME

profuse007

this valve stem and "shreder valve," are they the same entity? if so, ppl refer to them as fill valves, one on low side and one on high side.

if that is the case, the compressor is prolly at faulty. the low side pressure should be around 30-40psi at operating temp. sounds to me you got a negative pressure causes a massive vacuum.

btw, AC compressor only kicks in a range of pressure, not too and not too high. make sure the system is vacuum b4 recharging freon.

jdsdj98

Be certain that it is actually the Schrader valve that is at fault. I went through this exact scenario a while back with my '95 Tacoma. A shop diagnosed my leak as being at the Schrader valve. I subsequently paid them a handsome sum to replace the valve and recharge the system. 48 hours later I had no AC (or system pressure) again.

Beat my head against a wall tearing into the system behind the dash repeatedly, replaced the evaporator and the lines going from it through the firewall. Still couldn't seal it up.

This is the portion of the system that isn't visible in a leak test, since access to it necessitates disassembling the AC system, thus defeating the purpose of a leak test. Turns out it was simply the O-rings in the evaporator assembly (pressure switch, expansion valve, etc.).

Just for grins, leave the Schrader valve alone, tear the whole evaporator assembly down, replace the O-rings throughout, button it back up, and shoot enough R134 into the system to make the compressor kick on. I wouldn't run it for extended periods of time, since it won't have the full amount of oil in the system, but if it will hold pressure for 30 days or so, get it fully and properly recharged. That's how I fixed my problem that was originally diagnosed exactly as yours has been, and over a year later I haven't had to add any 134 to the system.

It was immediately apparent that the O-rings were bad when I removed them, as they were slightly flattened out. Maybe yours are shot, too. Ultimately, the only cost I should have incurred would have been the O-rings themselves, plus the vacuum/recharge fees at a local AC shop. I feel your pain.

profuse007

sounds more like a reasonable diagnostic. id give it a try.

burncycle2000

Ill definitely give it a try. This is why these posts work. Ill give it a look and post what happens. I do have one question. The shreder valve in it now is bad should I replace it and the O rings for the 30 day test? I know that dye is leaking out there.

jdsdj98

Because of my experience, I'm suspicious of any "faulty" Schrader valve diagnosis. Are you absolutely positive it's leaking? My experience was that I couldn't get all the dye/oil combo out of the valve anyway, since that's where you add refrigerant. That's the only part of the system designed to open & close and allow the refrigerant to pass in or out. For that reason, I don't think it's an easy part to diagnose as having a leak. There will always be oil/dye in the cup, even with a good one. I find it odd that after multiple valve replacements, you're still leaking. Like mine, that makes me think the Schrader valve isn't the problem.

Again, just for grins, forget the valve for a while and dig into the evaporator. It should be obvious if there's a leak anywhere in there. There'll be oil on the evaporator and/or inside the housing containing it. If you're unsure, put everything under a black light, as the dye you've been putting in the system will show up there, too. The cost of a pack or two of O-rings and a can of R134 will be less than $20. The system can only benefit from changing out the O-rings, and you may get lucky and plug the leak in an unexpected place. If that doesn't work, then move back to the valve as a possible culprit.

And just as an FYI, the Schrader valve we're talking about is not THE Schrader valve, it's just A Schrader valve. "Schrader" refers to the valve type, and is not specific to AC systems. Schrader valves are also found at the end of your tire valve stems, and on the valve stems of low end bicycles. That being said, I've never seen one go bad in any application, including the old one in my AC system. To this day, I believe that was a mis-diagnosis, as the system continued to leak after it was replaced. Keep that in the back of your mind in the process. Not to say they CAN'T or DON'T go bad, but I don't think it's common. I just think that's the first diagnosis when nothing else is apparent, since a technician could always put a black light over it and show you that there's dye in the cup. But I've been burned on that diagnosis, so my view may be tainted.

Finelygotone

This problem should be relatively easy to troubleshoot. I would:

Replace the suspected Schrader valve and filter/drier
Evacuate the system through a guage set
Preliminarily fill the system without the engine running until it won't take any additional
Start engine, set AC system fan to high - start compressor
Read pressures - if both high and low side are reading positive pressure (not vacuum) then proceed to fill system observing pressures
If system stays in vacuum on low side, there might be an obstruction or some other systemic issue that needs to be resolved.
The system should not run below 20 something psi on the low side....

After the wreck, was the system "open" for a period of time? This can wreak havoc with these systems and could be a potential source for your problem.

burncycle2000

The system was open for a long period of time. I will definitely crack into the evaporator and replace the O rings and take a look. I know that those valves were going bad, because when I would take them out the spring would be so compressed that it would not let the stem pop back up. Thats why I was thinking something was causing some type of intense vacume to do this. Thanks for all the advise Ill let you guys know how it goes.

leonardator

the schraeder valve itself only provides 80% of the sealing, the plastic caps provide the other 20%. also there are o-rings at every connection. what we do at our shop is charge the system with nitrogen and start spraying all of the fittings with soapy water, you will find bubbles near leaks. also if you pull a vacuum on it, it shouldn't lose more than 2 inches of vacuum over 5minutes after you turn off the pump. it's a lot easier to do than tear into the evap area.

jdsdj98

Again, my truck is the exact same model as this guy's. Like him, my diagnosis was EXACTLY the same as his, but was dead wrong. My leaks were in the O-rings of the evaporator. After having been into it several times trying to track it down, I can have my evaporator assembly out of the truck in less than 15 minutes. It isn't THAT hard, and I do think it's worthwhile to replace those O-rings if the A/C system is leaking and has no pressure. His problem may not be there, but the age of the O-rings definitely warrants replacement if he's digging into the A/C at all.

Again, I'm speaking from personal experience. This guy has described my problem and diagnosis exactly, and my problem was in the O-rings of the evaporator. Simple fix.

But my view's tainted based on a shop's incompetence....