I just finished replacing the head gaskets on my 98 STS and everything is great except the AC. I did the gasket job in the car and only disconnected the line running from the compressor up to the filter/drier. When I started the car it had no freon; however, I didn't get the expected dic message of very low freon, etc.... When I put my gauge on the low pressure side, it indicates it's full (I filled it today), but when the compressor kicks in, the gauge doesn't drop at all. I've searched many threads, but haven't found anything exactly like this. I'm sure the diverter door is working properly, since I can set it to 90 for heat and 60 for ac which it does change temperatures, but it's not getting as cold as it should. My ambient air temp sensor is fine as well since it had outside temps at 75 degrees yesterday. Any ideas or suggestions would be great. Thanks!

PS - Cadillacforums.com should sell T-shirts for people who have completed the Northstar top end rebuild :thumbsup:

Did you pull a vacuum before recharging the system?

:hmm:Thanks for the reply. Being the back yard mechanic all I have are handheld gauges and I use cans of freon to fill. I've never had any problems in the past, so not sure what's the problem here. Any ideas on why the low freon message didn't come on when I know for a fact the system was empty?:hmm:

Hmm, no you should have gotten a low refrigerant message & DTC if it where empty, But if you don't pull a vacuum, you leave moisture in the system that could freeze and cause a blockage somewhere. How about the low pressure pipe near the accumulator? Is it cold?

Yea, if you break the A/C lines open, you should vacuum them out before refilling with R134a. I did this last week to change an o-ring that was cracked/leaking and my A/C blows cold again.

Just got back from the shop and have some questions for you all. We pulled about 9lbs of vaccuum so there aren't any leaks, but after filling with 2lbs of freon, the compressor won't pull down much. At idle the low side is around 70 and I get basically no cooling. If I run the rpms up to 2500, it drops to about 40 and the system does cool. I'm assuming the compressor is bad, but want to see if any one here has some ideas. Does the system have a serviceable orfice tube or does the entire line have to be replaced? As always thanks for all the help!

I think you'll find the orifice tube at the connection on the firewall in front of the passenger (assuming the '98 is the same as the '97).

9lbs sounds a little low, you pull close to 30 and hold it, when it holds you know no leaks are present