A follow-up to "Bwa-Ha!"

[strotter]

I hate it when a plan falls apart.

 

Today was the first warm day in a while, 96 deg, so I was enthusiastic to take the newly a/c'd Z out for errands and be seen afield with windows closed. Driving to nearby Stockton at highway speeds, all was pretty good: cool (but not icy) temps coming out of the vents, enough volume to keep the cockpit quite comfortable. Good and good. One thing: at low RPMs but above idle, it made quite a bit of noise - sort of a "growling" noise that interacts with the exhaust note. Nothing too obnoxious, but maybe I'll look into one of the a/c mufflers mentioned in the JTR book. Undeterred, I continued into town, parked the car for an hour or so, took care of some business at work, eventually returned to the car which, for want of a better term, was basically a kiln.

 

Not to worry, though: I had the power of thermodynamics on my side! Flick the fan to "High", push the A/C button, and in only moments there'd be cool air on my fevered brow - only moments, coming pretty soon - moments from now there'll be - um, pretty soon the hot air will stop coming out of the vents, and cool my, uh. Man, it's hot in here...

 

Damn.

 

So, something has gone wrong somewhere, or was never right in the first place. Things on the list of things to check or change:

 

1. It is over-full or has leaked down. I'll throw the gauges on it tomorrow morning.

 

2. There's moisture or other contamination in the system. I have no idea how to check for this, other than to drain it down, vacuum, refill w/ a new dryer.

 

3. Air may be getting around the condenser. It's from a 280, and there's a good 3/4" gap all the way around it between the fins and the firewall. I'm thinking an air-dam of some kind around the edges (which I notice is present on both my girls' Civic, and our Dodge.

 

So the saga continues. Any suggestions of nuggets of wisdom would be greatly appreciated.

[baddriver]

I'm sure you already thought of this, but check to see if the compressor is turning.

 

I go through this every year because the connections on my old pressure switch are broken, and I soldered them back on. Generally during the spring tune-up i bump the wire, breaking the connection again, and then months later when I need the AC it's not there. two minutes with the soldering iron and I have AC again. I really should get a new switch someday.

 

A sudden failure when it was working hours before suggests an electrical problem to me, if it held vaccume for 24 hrs before you filled it, it shouldn't have leaked out already. Check the fuses and switches.

 

moisture in the system will generally cause the unit to stop working when it is already blowing out cold air - the orifice will freeze shut. It will thaw out a few minutes later and start working again. Insufficient airflow around the condenser will cause the compressor to work too hard (because the high pressure side will be too hot - and therefore the pressure will be too high) It won't cause your system to stop suddenly, but will shorten the life of the compressor.

 

Good luck.

 

PS just curious, are you using R12, R134, or a liquid petroluem mix (like duracool?)

[strotter]

Bad, I'm using 134 - it ended up that it was available everywhere, all the documentation nowadays talks about it, just generally the "done" thing.

 

I went out to the local Pep-dudes store and got one of those Chiltons "How to fix your heating & a/c systems" books. Probably should have done that before I started this whole thing, eh? I mean, the factory shop manual goes into extreme detail about every aspect of a GM system, and I also have a 260z shop manual, but, man, in both you have to understand all the other chapters before you can understand one. The Chiltons is kind of an "Idiots Guide to Cool Air", right up my alley. It has a really good troubleshooting section, broken down by "The high side reads this; the low side reads that; if this pipe is cold and this one is warm, check the so-and-so..." Yes!

 

So it looks like I'll be reading for a couple of days, and taking some notes.