I am still battling poor AC performance. So far, I have changed over to the R-134a and replaced all hoses and compressor. I have checked and cleared the condensor of debris...I have also played with the switch screw settings and best I can achieve consistantly is 54F vent temp at highway speed (85F outside temp).

The books and corvetteforum members tell me I should see 40F at the vents. To complicate matters, the blower will shut off periodically and restart after a few seconds. To resolve this, I opened up the control assembly (under the radio) and found evidence of shorting - melted wires. I removed the plastic connector altogether and soldered the wires in place. I suspect that the blower motor is not functioning well, perhaps it is drawing too much current and blowing the circuit breaker?

Here are my questions:

1.If the blower motor was not turning as fast as it should, would this reflect higher vent temps?

2. The evaporator inlet pipe is quite warm to touch and the accumulator is cold. Is this normal?

3. I have replaced the UPPER pressure switch (on a line to/from accumulator) with no improvement. I just noticed that there appears to be a second pressure switch lower down on a second pipe (on a line to/from the evaporator). Can this be adjusted with a center screw like the upper one?

This is really frustrating me...particularly because I cannot seem to find a good AC person.





[Modified by redvette1986, 10:27 PM 7/28/2003]

 

The switches on the high pressure line (small one) are fan (disconnect it & the radiator fan comes on) & high pressure cutoff (disconnect it and the compressor shuts off). Neither are adjustable. The high pressure switch opens at 400psi or so and generally, if they're bad, they stay open regardless of pressure and the a/c doesn't work. If it is opening while the compressor is operating, the system is probably restricted on the high side (look for an icy spot) or air flow is severely reduced. You want it to open if the pressure is too high, otherwise everything blows up. Low blower speeds result in higher vent temps. Max with electronic air is controlled by the dash assembly and when you put it on 60, it's suppose to ignore the signals from the outside and inside air thermistors and keep the blower at max. I've had several in my Vette that would do this for awhile and then reduce blower speed to what you get on Manual 10 (still high, but not as high as it can go) and then after a couple of minutes, go back to max. New controllers (actually they're all rebuilt) fixed it for a year or two and I'm on my third one now. Both the lower and upper tubes at the evaporator should be the same temp (cold, not hot) or the upper a little bit cooler. Make sure you take your temp readings at the very bottom of the evaporator, below the orifice. You can also compare temps with a digital thermometer. If the bottom is hot, after the orifice, the orifice is probably plugged or the charge is too low, though with either condition, the compressor would cycle on & off quite a bit.

 

I have a question I resently converted mine to r134. The a/c seems fine and blows cold but it does not seem to cycle. It will cycle when the system was empty though.

 

It cycles when it's low or the orifice is plugged because the little that's there immediately boils as it passes through the orifice and there's no oomph left by the time it reaches the low pressure switch. Cycling can be hard on the compressor and have a detrimental effect on idle. That's why later systems incorporate a thermistor in the pressure switches, shut the compressor off all together and throw a code and/or, GM uses a variable displacement compressor on some models which never cycle. Above 70 degrees, it shouldn't cycle at idle and for your locale, it's probably closer to 100 than 70. Try checking it at night or you may have to wait a couple of months. However, if you want to check it; disconnect the blower motor harness with the a/c at max. You can try this test at idle and with the engine at 1500 to 2000 rpms. The reduced air flow should allow the pressure to drop enough for the system to reach the cutoff threshold. If it doesn't, but the vent temps are good and there's no ice (or the system doesn't go warm all of sudden at cruise which would indicate that the evaporator is icing over), you're probably still ok. The other possibility is that it's overcharged, but if you started empty and put in 80% of the R12 amount or no more that 2.5 12oz cans, it's probably right on.