I have a bit of a problem with my A/C. First. . .the car: 88 L98 with 4+3. Z52 with most options. The previous owner had most of the A/C system replaced and updated to R134a. When I first start out in full auto mode, it blows very cold and very strong. After about 20-30 minutes of driving, it slowly blows less cold and less fan power. If I turn the fan to manual, it still doesn't seem to reach full speed. Eventually, on hot days, it no longer keeps up. If I turn it off for a few minutes, then turn it back on, it blows cold and strong again. Any ideas where I should start checking?
Thanks.

 

These cars are sports cars not refrigerators.....I got an '89 and this sounds normal to me...put it in manual and let it run for a minute or 2 and see if the fan speed picks up.

Here in Florida my AC has a hard time keeping up when its over 90 outside but the thing will freeze you to death when its cooler than that. I also run the 134A conversion since I have a slow leak in the system...I use a small bottle ($5) once a year to just top it off. Check to ensure the system has the proper level of coolant in it....clean the crap out of the fresh air intakes under the wiper blades, clean the condenser coil unit in front of the radiator and then go from there.

P.S. On really hot days, I like to pull up next to people in other cars with no/broken AC and act like I'm shivering and freezing to death in my car...try it -- its good for a chuckle.

 

Actually, even at 98°F mine will cool you like a refrigerator for that first 20 minutes or so. I actually do get cold. I was thinking maybe something to do with the computer???

 

.....ck your pm's....

 

I would first try to determine if I had a freon related problem, or a air blend problem.

I don’t think its going to be freon related though because its not characteristic. I’m putting my money on a blend related problem. You need to find out what the blend door is doing when the problem occurs. Look in the evaporator housing by removing the blower module and look in. See if the door is in a different position. Also check the connector and wires on the module for any corrosion or loose pin connections.

But if the door moves and the blower reduces in power, the A/C controller might be going bad.

Just a couple ideas and a few places to start.

 

Often the evaporator will freeze up and that will restrict both air flow and temperature. Does it happen more in stop and go or Highway driving?

 

With the super hot & humid summer we have had, this makes some sense...

Doesn't solve the problem, tho.

 

Believe me........I know. Poor design I'm afraid. The evaporator doesn't freeze solid. Just enough to inhibit cooling and airflow.

BTW.........I slayed the dragon 4 times.........

 

I get cold A/C, but when I turn the temp up, the thing quits blowing air. I've noticed it only blows cold air on defrost.

I ran the car with the heater on 90, even though I didn't feel anything. I checked and both heater hoses were hot.

 

In 85 the heater only blows from the floor vents and a/c from the dash vents (unless its set to bi-level)

 

At the Auto 60 setting, it should blow max and stay cold. Either the evaporator is icing over or there's a problem with the Blower Module and or Control Panel. To check it out, drive it around and when you feel a reduction in flow and coolness, get it in your driveway and either check voltage at the Blower Motor - should be 12 or greater; or jumper the Blower Motor directly to the battery and see if it's any stronger. If not, check for ice on the Big Line exiting the top of the Evaporator Case. Otherwise, hookup a manifold gage set and with it set at Auto 60, unplug the Blower Motor and note the Pressure the Compressor cutsoff at. It should be no lower than 22.5 psi. If it is lower, disconnect the Low Pressure Switch harness and turn the adjustment screw between the terminals 1/2 turn clockwise. Retest, adjust, until the cutoff threshold is at least 22.5 psi but less than 25 psi. If it won't adjust, replace the switch. Post any results you get for further help and if you can, get the operating pressures, high and low, along with the center vent temp, noting the outside air temp. Obtain this info with the engine warmed up and running at 1200 to 1500 rpms and the fan switch disconnected so that the main fan is running.

 

Also check that the condenser is free of dirt, leaves, paper etc.

 

As said if the low side pressure is to low it could ice up. Low freon will do this also and a set of gauges would be a great help. It just might need a little freon added.

 

Thanks for all the advice. While I haven't had time to try any of the diagnostics you've suggested, I did drive the car to work and back today. It's 90° and fairly humid today. On the way home I thought I'd just try not turning it down so cold to begin with and see what happened. So instead of 60/auto, I set it at 69 with the fan manually on 7. It did perform better, not perfect mind you, but better. After about 20 minutes the temp started to rise somewhat, but it kept me cool pretty much all the way home (I did eventually lower the temp setting to 66 and raise the fan to 9). Just before I got home I turned the AC to econ and drove about 2 miles then turned it back to auto (did not touch the other settings). Once back to auto it was real cold again. So does this tell me anything?

By the way, I have very little stop and go traffic as I live out in the country so this is happening while I'm moving along at highway speeds.