A thread for random questions with short answers

1. My 1991 Mercury Tracer LTS has an R-12 aircon system that kind of works. It will turn on and blow cold air for about two minutes before it stops and summer air once again blows through the vents. I want to buy some Freeze-12 so I can top off the system. To buy Freeze-12 you have to have an EPA 609 certification. Any advice on what is the best (cheapest) place to obtain this certification? It seems to be an online test. Also, if there is an R-12 alternative that is better than Freeze-12 let me know. I have no intention of doing all the work of converting the system to R-134a. My friend has a vacuum pump and refrigerant capture setup he got from his dad when he retired and closed his auto shop.

2. I have changed some timing belts. The procedures have pretty much always said not to rotate the cams opposite of the direction they normally rotate. What bad things can happen if you spin the cam backwards? Is it something that is probably only bad if you do it really fast or do it on a vehicle with big lumpy cams?

3. Is the 2.0L 8V motor in a 1996 VW Golf interference or not?

I got my Freon certification in 1996 for about $20 (if I recall) from MACS, Mobile Air Conditioning Society. It was a mail-in test that was pretty simple. I'm sure something's available online now.

2) Never heard of that one for any specific reason, but usually you can get valve contact if you go too far that direction.

3) At full cam lift at the same time as TDC, yes. Sometimes you get lucky though, I did on mine. Broke the belt, installed a new one, good to go.

Craigslist sometimes has some R12 on it. I got a can for free once in a box of other car parts but now I can't find it :) If I knew where it was I'd send it to you.

I think more importantly is why its not staying cold. If the system were undercharged, chances are it would be warm until you reached a certain RPM where it made enough pressure differential to get cold. I doubt it would be cold at first, then warm the rest of the time. I would suspect either the compressor or a restriction in the dryer, but there is no way to tell without a manifold to check pressures.

My friend has a set of those gauges. What exactly am I looking for?

What do you mean "all that work" to convert to R134? You draw it down, and recharge. Is that really a lot of work to you?

Rotating an engine backwards has you pulling the belt tight across the tensioner side. You're faintly more likely to have a belt or chain jump a sprocket tooth this way.

I was under the impression that R134 would cause all the seals to leak. I dont want to replace the seals or the part of the aircon system that is in the dashboard.

I've done a few "dirty" conversions where I just sucked out the R12 and put in R134. It works poorly for a while, but will never be really cold. There are three main problems:

1- R134 needs a PAG lubricant instead of the Ester lube in an R12 system

2- Most R12 systems use an orifice tube and R134 uses an expansion valve. The R12 evaporates a little easier than 134, so the expansion valve is a necessary upgrade to coax 134 to evaporate properly.

3- R134 also needs a bit more condenser heat transfer to properly convey the heat it absorbs.

My co-worker has a C20 pickup that he did a dirty conversion. It will keep the cab of his truck a little cooler than outside, but fails miserably on a 90+ degree day. In his truck you just sweat 20% less than if you had the windows down.

I've had 3 cars with "dirty" conversions. They work great, for a while. I recharge every 9 months or so. I'm sure R12 would be better, but this is cheap and cools down to 50 degrees or so in 90 degree weather. As good as any of the other 4 Miatas I've owned.