Weak A/C, needs R134? blend door staying open? thermostat?

[jmcr]

Hi guys,

Having a problem with the A/C on a 98 EB 5.0L. I set it to the coldest, 60, on 'Max AC' setting which I think closes the intake door to recirculate the air, but its still blows just slightly cool air. Its about 90-95 degrees outside.

I've been searching the forum and trying to find out what the cause might be. I've read about the blend door being a common problem, but if its set to Max AC doesn't that remove the blend door as a cause for weak A/C?

I just checked the pressure when it was 70 degrees outside with Max AC running and saw that the compressor seemed to cycle on and off every 2 seconds or so. The pressure would go from 20PSI to 40PSI and the compressor would make click each time. Does anyone know what this indicates? I thought the compressor would stay on steady at Max AC set to 60. Is this a thermostat problem? Does it just need more refrigerant or is something else wrong?

Any help would be great.

 

[John Frank]

If the blend door is stuck it will effect whatever the temp setting you select including max a/c.

I think max a/c setting will just try and set the blend door to closed (a/c only no heater core added), drive the compressor as hard as it can and set the cabin interior fan at high speed.

I also think (not sure though) that the compressor will still cycle on and off.

There are posts you can search for on how to check the blend door if no one else jumps in that tell you more than the little I know about it.

 

[my98nnj]

I just checked the pressure when it was 70 degrees outside with Max AC running and saw that the compressor seemed to cycle on and off every 2 seconds or so. The pressure would go from 20PSI to 40PSI .

Pressures are way low, you definitely need a recharge.
Have a shop with an A/C tech machine do the service. It's the only way to correctly charge an R134 system. Should run you about 80 bucks.