'87 AC Cycle Time

[mgbeda]

Thanks to Dr Lebaron and his vacuum hose info I now have WORKING AC! At least it seems to work- it's only been in the 70's so it's not like it's had a tough test. But I'm wondering if the compressor is cycling too much. I timed it and it seems to run about 14 seconds and then shut off for about 10. Does that sound normal, or like it's a little low, or like it's very low? My car is still R12 and I'd hate to hook up a $40 can (if you can find it) only to find out it only needed 2 oz of the stuff.

Thanks,

-mB

 

[Aspen500]

At 70 degrees ambient, that cycle time sounds reasonable. The big question is, how cold is the air out the vents? Should be in the high 30's (when it's 95 and humid out, it'd be mid to upper 40's most likely). If there's a sight glass on the dryer, see if there's bubbles. With R-12 a full system should have no (or very few) bubbles. With R134a bubbles are normal since you only use about 80% of the R12 capacity.

If it was really low you''d not have very cold air and it may cycle every few seconds. The only way to really know if it has the correct amount of refrigerant is to recover what's in there and recharge with the listed capacity. What I mean is, too much refrigerant is as bad, or even worse, than too little.

 

[mgbeda]

Ah, the sight glass. Where is that? It says in the manual it's on the dryer, but I don't see it... Might it be under a screw in cap (red arrow pointing to it in this picture)? I didn't want to unscrew something on a AC line without knowing what it is.

Thanks,

-mB

 

[Aspen500]

It should be on the top of the dryer, where that hole is. Maybe the dryer was replaced at some point with an aftermarket unit that doesn't have a sight glass(?) and I've also seen them painted over. Not sure what year your car is but, some manufacturers eliminated the sight glass starting in the mid '80's from what I remember. Bean counters you know

Don't try to unscrew the cap! Then you would be low on refrigerant. It's the high pressure relief valve. In case of a system malfunction that causes high pressure, it vents it off. Somewhere around 450-500 psi is when it opens. It's the brass cap in my photo.

This is the one on my car ('79 Aspen):

 

[mgbeda]

Thanks a bunch, Aspen500! Phew, glad I asked about that "cap". I was thinking of the sight glass on my '75 Buick, which is about 1/2" wide and inset. Maybe that little circle on top IS a sight glass, just covered with dirt, or maybe it's where they used to put it (mine's an '87). Anyhow, thanks again; now I know what I'm looking at. By the way, that's one immaculate engine bay!

 

[BudW]

I’ve modified your picture a bit.

The high-pressure pop-off valve is where you marked the red arrow (which I made larger for you).
The sight glass is painted over and is marked with my orange arrow.

Get a sharp object and the (black) paint will scrape off easily.

If you are using R-12, the sight glass needs to be clear (with A/C operating) and then add ¼ can (or ¼ pound) additional. Note: the sight glass will be clear if system is empty, as well. If you can view bubbles in the glass, then keep adding R-12.

If using R-134a (if car was retrofitted to R-134a) – the sight glass will be useless for determining when system is full. The sight glass only works for R-12.
BudW