Prom Chips

[Guest grkman1]

Can anyone tell me how much for the 2 prom chips for the BCM, and if they are defected, would they control such things as the A/C which cuts out on mine because of false readings from the computer saying that I have low fluid in the system?

This is what I am getting from my mechanic. He just chasnged out the A/C and it works temporarily and shuts down...He says is from the BCM and the 2 chips have to be changed. Please let me know before I give the AOK for the work to be done

Thanks

[padgett]

Possible but unlikely, the two chips are a 27C256 and a 2816 but that will not help as they have to be programmed.

Did anyone check the reported ac pressures using the diagnostic mode ? Might be the low pressure switch.

[Guest grkman1]

I have replaced the BCM chips, I was getting a code B556 History. I unhooked the battery and now I have no codes, but I do show errors when I do a diagnostic test for everything, and the Air conditioning still doesnt work...any suggestions?

Is there a way to program the chip/chips (system) from the CRT? I am very discouraged and frustrated. I have a brand new AC system, New chips, new ignition switch (that has messed up my tilt wheel and key now sticks in on position) and still the A/C doesnt work

Help please

Thanks

[padgett]

B556 meant the 2816 had a problem. History means it went away. Now if you look at page 1C-16 chart A in the 1988 factory service manual you will see that the BCM just receives the low pressure signal, the a/c relay is driven by the ECM. Since you are apparently not getting any eror codes relating to the a/c (I hope you do not mean the errors from the STATUS screen - those are samples, not real codes)- real codes would be B446, B447, or B448.

Page 1C-10 lists all of the diagnostic checks you can make. One thought: the system uses less R-134A than R-12. If overfilled, the compressor would run until an overpressure was reached and then shut down. This can be checked by monitoring BD-27 - over 200C (the readout is in degrees) and it will shut down. Low pressure can be checked at BD-27. With the engine off and cool, both should read about the same. I have not driven mine today and BD-25 through 28 all read the same thing, 25C.

If everything is mechanically correct, my guess is either one of the pressure switches or the a/c relay.

If all looks good, the next step is to instrument the a/c signal from the ECM to the relay and watch BD-27 and 28.

The good news is there is nothing unusual about the Reatta A/C from any other GM ATC of the period except for its ability to diagnose through the CRT.