96 deville /north star a/c problem compressor will not engage

[ml edmondson]

a/c compressor will not engage on my 96 deville with 4.6 north star, is there something I have to do to reset pcm for a/c operation it has the automatic climate control system

[BodybyFisher]

There is probably a code set for low freon. Go to my signiture, and follow the directions for checking the codes, check the codes you probably have one of these codes

B1347 - Very Low A/C Refrigerant Warning

B1348 - Very Low A/C Refrigerant Pressure

Follow the directions to erase the codes and the compressor will engage so that you can charge the system

[caddydeville05]

I just got my ac system recharged with freon today, no leaks but compressor want engage. My ac relay fuse was bad so I replaced that and compressor still want engage. Before adding freon I was getting the ac compressor off very low refrigerant notification. Now that it's recharged I'm still getting that notification. The weird thing is the only current codes I have are PCM P0420 and IPC U1255. Not sure what either of them mean. I tried disconnecting the negative side of battery and still nothing. Seems like we are having a similar issue. Any luck with getting yours fixed?

[Göran W]

U1255 - Class 2 Communication Malfunction (Serial Data Line Malfunction) Maybe this is your obsticle?

P0420 - Catalyst System Low Efficiency

[KHE]

I just got my ac system recharged with freon today, no leaks but compressor want engage. My ac relay fuse was bad so I replaced that and compressor still want engage. Before adding freon I was getting the ac compressor off very low refrigerant notification. Now that it's recharged I'm still getting that notification. The weird thing is the only current codes I have are PCM P0420 and IPC U1255. Not sure what either of them mean. I tried disconnecting the negative side of battery and still nothing. Seems like we are having a similar issue. Any luck with getting yours fixed?

How did you recharge the system with the low refrigerant code set??? The code needs to be cleared, the system evacuated with a vacuum pump, the refrigerant supply hooked up and air bled from the hoses and then charged until the system won't take any more refrigerant. The engine is then started and the A/C turned on to pull the remaining charge in.

[caddydeville05]

So I was suppose to clear the codes before getting the freon added? Basically I pulled up and they hooked up the machine, added only 1lb of freon and said it was full now but it still wasn't blowing cold. Now I understand why bc the compressor wasn't engaged so therefore wasn't able to suck in the freon is that correct? I'm starting to wonder if I paid for him to just tell me he filled it with freon when actually it didn't even take the freon to begin with? So what now, should I take it back and clear codes first then have them top it back off with freon? Should this make it work or do I also after clearing codes unhook negative side of battery then hook it back up to engage the compressor then add freon? Thanks in advance for yalls input it has been a lifesaver.

[Göran W]

Begin by just clearing the code! I think it can be done from DTC on Your car. There is a "How to" and a complete list of codes in link from BodybyFisher above.

[KHE]

So I was suppose to clear the codes before getting the freon added? Basically I pulled up and they hooked up the machine, added only 1lb of freon and said it was full now but it still wasn't blowing cold. Now I understand why bc the compressor wasn't engaged so therefore wasn't able to suck in the freon is that correct? I'm starting to wonder if I paid for him to just tell me he filled it with freon when actually it didn't even take the freon to begin with? So what now, should I take it back and clear codes first then have them top it back off with freon? Should this make it work or do I also after clearing codes unhook negative side of battery then hook it back up to engage the compressor then add freon? Thanks in advance for yalls input it has been a lifesaver.

The system is NOT full with 1 lb. of refrigerant in the system... The system capacity is 2.0 lbs. With only half the refrigerant in the system, the low refrigerant code will set and the system will not blow cold air because the compressor is disabled.

Get the refrigerant hooked up to the system, burp the air from the charging hoses, open the valve on the low side charging hose to let the refrigerant to the accumulator. Then start the engine, enter diagnostics, select ACM CODES, when CLEAR ACM CODES appears, press the fan up switch to answer "yes" and the system will pull in the remaining charge.

[caddydeville05]

Ok bet I'm going ti get on that first thing in the morning. I wouldn't have known to do any of that if it weren't for you guys giving me this advice. I will be sure to let yall know what the outcome is in the morning. Thanks again.

[rockfangd]

That is correct. the system capacity is 2.0lbs R134a.

once you clear the code it should pull the rest

[caddydeville05]

Update: I cleared codes and hooked up the r134A and it took the 1lb I needed and apparently it didn't work bc it's still not blowing cold. So I disconnected neg side off battery and cleared codes again then hooked up to low side port and checked psi was at 45. Still blowing hot bc compressor just want engage. I'm at the point of giving up, can't afford a new compressor and I'm definately not goin all summer without air.

[KHE]

When you charged the system originally, did you use a vacuum pump to evacuate the system and charge into the vacuum? If not, then you have air in the system which will increase the head pressure and if there is any moisture in the system, it can freeze at the orifice tube.

[Cadillac Jim]

Be sure that you have identified any CURRENT codes or codes that reappear after you reset the codes. If you are disconnecting the ground terminal of the battery to clear the codes, that will set the B1652 and P0603 codes.

There are quite a few codes that can be thrown by the A/C sytem. B1310 through B1319, B1340, B1341, B1347, B1348, B1350, B1981, B1982, U1016, U1064, U1064, U1069, U1152, U1153, U1169, and U1255 are given on page 1C-10 of the 1997 FSM. If there are no codes and the compressor will still not turn on, either the compressor clutch or its wiring is bad (which probably would throw a code) or, as KHE just said, there is air or water in the system.

[caddydeville05]

The ipc u1265 keeps coming right back after I clear codes. I did disconnect battery terminal and got that other code but I cleared it and it didn't come back after that just the ipc u1255.

[Cadillac Jim]

Which module throws the U1255?

[caddydeville05]

IPC U1255 is the only current code I have? Yea we did use a vacuum to evacuate it first then I clearrd the code and it took the 2lb and was blowing snowballs until I got about halfway to my gf house which is 30 miles from where I was and it abrubtly changed back to blowing hot air.Run codes again and its IPC U1255 current thats it. It took charge fine and was blowing cold then just stopped. Don't know what else to do I'm stomped. I did get b1340 when I unhooked negative port on battery but I cleared that code and it never came back. Everytime I clear ipc u125 and say I run diagnostics again right after and its current again.

[Cadillac Jim]

You have two topics on this problem. First, it's very important to determine which module threw the U1255 code because the troubleshooting for fixing this is a lot of work and it is different for each module that can throw the code. We can just assume that the ACM threw the code and go forward but if it isn't that is a big waste of time and a lot of work.

The way to tell which module threw the code is to run the codes from the A/C buttons and watch which module is listed just before the codes is displayed as CURRENT. Sometimes the module is displayed along with the code, as in

ACM U1255 CURRENT

on the driver information center. Please let us know for sure that it is the ACM that throws the U1255 CURRENT code. If it is, look at my post of the troubleshooting procedure, right out of the 1997 FSM, from the other Topic here.

[caddydeville05]

The current code I have is IPC U1255

[Cadillac Jim]

Which module is throwing the U1255 CURRENT code?

This is very important because the U1255 is one of the very few codes that can be thrown by any of several modules. The process of troubleshooting this code is very different for the different modules. One module that can throw this code is the ACM and this could account for your problems. Or not. Run the codes again and write down exactly what is displayed just before the U1255 CURRENT is displayed. In particular, if it displays "IPM U1255 CURRENT" that is one thing, "ACM U1255 CURRENT" is quite another.