ACC error code 38 - data line failre PCM

The AC compressor does not engage on my 91 PA. The system was charged and tested, and the compressor does work when wired directly to the battery.
I checked the error codes as per Hotz28 advice in another thread, and it gave a 38. I cleared the code and put the ignition in run again and repeated the procedure. It gave a 38 again, so it does this immediately without me actually using the climate control.

What does this mean and how can I fix it?

Also Hotz, I would be interested to learn the other functions of the ECC such as monitoring sensors and vehicle speed.

How did you charge & test the system without the compressor running? Code 38 means that the power to the controller was disturbed, most likely by disconnecting the battery. Go through the procedure again and see what happens. Turn the system OFF and disconnect the negative battery cable for 30-sec and reconnect, then go through the reset procedure. If no go, you may have a bad pressure switch. Try jumping the pressure switch on the low side with a jumper wire to see of the compressor will engage. If you have a blocked orifice screen, the the compressor will cycle until the high side pressure switch shuts it down. You have a PM with the procedure for checking other parameters (data) using the ACC control.

Thanks for your answer, I went to an AC specialist who wired the AC compressor directly to the battery. The compressor clutch engages then, and he could charge the system. He also tested the low pressure switch and it was ok. With the AC compressor wired to the battery, I put the blower on and immediately the vents blew cold air so he said he was sure it was some kind of electronical problem "inside".

I will follow your procedure and report back, but before I disconnect the battery I will check for other codes (they will be cleared if you disconnect the battery?)

I resetted the ECC, but it still gave a code 38 (as well as a 152, battery disconnected)
I started the engine and put the AC on 'auto' on the coldest setting. The clutch of the AC compressor now engages and disengages with intervals of about 10 seconds!
There was cold air coming from the vents, but I can't say for sure if this came through the AC since the ambient temperature was only about 50 degrees.
Still, the intermittent engagement of the compressor is more than it has ever done before. Does this give any clues ?

I was unable to retrieve any PCM codes or see sensor functions. "hi" and "low" cycle through 0,1,2,3 and pressing 'ext temp' does nothing.

I can't say for sure if this came through the AC since the ambient temperature was only about 50 degrees.Actually, the compressor should not come on if the ambient is 50 deg or less. Wait until it warms up to see what it will do.

The complete diagnostic functions may not have been available on 1991 systems. It did work on my 92 PA & 93 LeSabre.

Today was a bright and sunny day, and the temperature was 60 degrees, so I took the PA out for a 20 minute drive to test the AC.
According to the ECC it was 12 degrees (54,5 F, I don't know why it is in Celcius while it is an US import), but it is always about 5 degrees C too low.

I put it on auto and on the coolest setting. The air blowing through the vents was notably cooler than the air flowing through the window, so the AC was working.
The AC worked the whole ride. On 2 occasions I stopped briefly to check on the clutch, it was engaged most of the time but sometimes it disengages for a brief period. The lines from the accumulator were icy. Still, it gives a 38 code. But it cools!
Does this sound like normal operation?

At 60 deg ambient, the compressor should cycle and that is the function of the low side pressure switch. Due to the lack of demand and when the pressure drops too low, the switch will disengage the compressor clutch. The code 38 seems to be persistent at this point, but it may clear itself after about 50 ON/OFF ignition cycles if no problems are detected. Other than the code, it sounds like your system is working as designed. Good luck when it warms up!

Thanks for the help Hotz :) I hope it will keep working through the summer.

You are welcome. BTW, what average temperature does your part of Holland experience in the summer, mid 70's - 80"s, or higher?

The average maximum summer temperature is about 70 degrees. But it can be really stuffy and you are often stuck in traffic jams for hours in which it will really get hot in the sun so having a working AC is great :)