80 Series Aircon

dasher,
Sounds to me like it is suffering from low refrigerant level.... "short-of-gas."

BUT.......

Although I am a fridgie, I have very little knowledge on auto air conditioning.... I had mine serviced recently as it was showing similar symptons, although mine doesn't have a sight glass. It was short, and now works a treat!

Just my opinion

Brian

Dasher,
Had a similar problem on my 80 DX a few years ago, AC would just come on/off when it pleased, the fix was a new TX valve.

Cheers Drew

Most likely low gas or faulty valve within the system

Hi there Dasher, is it genuine air or after market ?? Genuine will be nippondenso and will be tagged on the compressor, it sounds to me that the evaporator under the dash is freezing up after a period of time which will stop cold air flow till it defrosts itself. Next time it happens especially on a hot day put your fresh/recirculate control onto fresh and suck some hot air through and see if that solves the problem if so then the thermostat will need turning up a bit. BY about 1 to 2 mill clockwise. If its genuine air then as mentioned above it could be the tx valve playing up. If its genuine air then you cant adjust anything. Does it cycle on and off ok eg can you hear the compressor cut in and out. You will hear a click from inside the engine bay and if genuine, idle speed should increase and then drop back to normal idle speed when compressor cuts out.This can also be observed by the clutch on the front of the air compresor spinning when engaged and not spinning when compresor disengaged. The sight glass you are talking about should show a small amount of gas sitting there when air is off. When you turn air on this will show bubbles for a quick second or two then should be clear no foam. If foaming while air compressor is engaged then it is low on gas. (I dont think this is your problem) The other thing it could be is the high/low pressure switch playing up. An easy way to test that is next time it happens grab yourself a bit of 4mil wire or the likes and disconect the two wires running into pressure switch then just bridge the two wires with the 4 mil wire if this makes the compresor cut back in then its the switch. Hope this gives you a few things to look at ans save a few $$$. Regards Steve M

Hi Stephen M,
it is genuine Toyota,
where is the pressure switch that you mention located?
Many thanks,
dasher