Recovery vs. reading the gauges?

[iXod]

I'm a DIY'er on my car (2004 Mazda 3) for most things. I've got a set of gauges (converted from R-12: thoroughly flushed; R-134 quick connects added) and can taps, etc. I don't own a pump or other accessories so can't do a replacement, only add as needed, trace leaks, etc.

The AC will put out only about 50 degrees air on a not-so-hot day (70). My local AC shop said that the only way to treat this is to remove the R134 and weigh(?) it. Then replace the specified amount.

What happened to reading gauges? My rudimentary understanding of troubleshooting is that by reading the pressures and knowing the temperatures, you can determine whether the system is under- or over-charged, and other mechanical issues (compressor, valve, blockage, etc.)

I agree that the only way to know--absolutely--if the correct amount of refrig. is in the system is to recover/recharge, shouldn't a competent tech be able to also determine this by use of gauges?

Thanks.

[Dougflas]

The short answer is...yes and no. An experienced tech can usually get it close but the BEST thing to do is recover and recharge by weight. That way, one can rule out the refrigerant charge as a problem. The most common problem is refrigerant charge.

If you had a cycling clutch system that used an accumulator, an experienced tech could measure the input and output temps of the evap. They should be the same or the output slightly colder. But still, today's AC systems use such a small amount of refrigerant, a few oz could mean 30% of charge.

[iXod]

Thanks for your reply. I guess I'll go for the recover/recharge.

Also, the driver's side vent is 8 degrees warmer than the dash center vents. Is this a clue to the cause? Or possibly another problem?

Thanks.

[DetroitAC]

I agree with Dougflas, with experience and the right instruments you can diagnose under or over charge and adjust it by adding or removing in small steps. BUT, I can't even find those instruments in the amount of time it would take to just recover and recharge. Recharge by weight is the bulletproof way of getting the charge right.

Warmer driver vents = undercharged

[iXod]

Thanks for your reply. Sounds like I have a recharge in my near future. (c;

Warmer driver vents = undercharged

How does undercharge cause warmer air in one vent? Just curious...

Thanks again.