Air Conditioner problem on 91 corolla

Hi my 91 corolla hove some problems. When the engine is travelling at 2.5-3k rpm the air con is much cooler. However while idling at 1.2k the it is not cooling at all.
I've measured using a pressure gauge manifold that while idling the pressure on the firewall after the eveporator is around 70 psi and 40-50 psi in higher engine speed.
Anyone can advice if it is under charge refigerent? (I understand a good system should not leak).
Regards, Richard
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The easy way to check refrigerant charge is to look at the sight glass on the receiver-drier. The receiver-drier is a cylinder mounted in front of the condenser with a small round glass window on top. When the air conditioner is running, it should look like clear water running past the sight glass. If you see white foam moving past the sight glass, the system is low on refrigerant. While a good system should not leak, it is normal to loose some refrigerant over time, especially if the air conditioner is not used for long periods of time where the seals can dry out. If your air conditioning system has never been recharged in 17 years, I'd say that the system was well-sealed.
When you measure manifold pressure, you need to give both high and low side pressures, with the engine at 2,000 RPM and the system set on recirculate, max cold, highest fan speed.
Also check to make sure that air flow through the condenser and radiator are not obstructed, and that the electric condenser comes on when the AC is engaged.
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Ray O
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Hi Ray O
Thanks I've seen the sight glass on the dryer bubbles during operation. Any idea if I can identify the refrigerant in the system as I underestand R12 has been discontinued years ago and this car is bought 2nd hand 1yr ago. Can R134a be subsitute for R12 in you experiences?
Regards, Richard
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If you see white foam in the sight glass, the system is low on refrigerant. I am pretty sure the original refrigerant in a 1991 Corolla was R-12. R-12 is not compatible with R-134A and should not be mixed. The system can be converted to R-134-A, with the first step being evacuation and recycling of the R-12. I forget all of the steps involved in conversion, but a competent shop should be able to do the conversion for a reasonable price.
If the system was previously converted, there may be a 134-a sticker somewhere in the engine compartment.
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On Mon, 8 Oct 2007 20:01:32 +0800, "Richard"

If the car has been properly converted to R-134a you will see two big clues - they will have fill port adapters permanently attached to the compressor access fittings to take the new snap-on R-134a style fill ports, and a sticker on the radiator support with the new refrigerant type and fill quantity information.
If the car is still running R-12 you can keep using it on R-12 - for now it's still cheaper to top off the system with R-12 than to convert it over. R-12 is a bit pricy, but it is still being made overseas in smaller quantities.
Try to avoid conversion, doing it right costs a LOT - you have to either replace the compressor, or remove it to drain and flush all the old mineral oil out and fill with synthetic oil. (The system needs to be below 1% residual mineral oil, or the R-134a gums it up.) You need to change the filter/drier because it collects excess refrigeration oil, you should change the condenser coil behind the radiator to get needed extra capacity, and you may have to change the metering/ expansion valve.
No AC system is totally gas-tight, R-12 or R-134a they still have hoses and seals that can have minute seeps. So if it loses a pound of refrigerant (about where you will notice a loss of cold) every 5 to 7 years that is still on the ragged edge of "normal".
If they run an electronic "sniffer" refrigerant leak checker over all the hoses and seals (including the compressor shaft seal) and don't find any leaks big enough to set off an alarm, it is tight enough to refill and keep using.
If they do find a detectable leak, you need to recover & evacuate the system and fix it. And there is value in the residual R-12 they recover from the car, you should get some credit for it...
--<< Bruce >>--
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