My suburban's A/C system is blowing warm air through both front and rear systems even with airflow across the radiator. The compressor is spinning but not cycling. I put a gauge on the low pressure side and it looks like there is a sufficient charge of R134a (about 40 psi). I performed a visual inspection of all lines and associated A/C equipment and everything looks fine. The radiator is clear of any obstructions.

My experience working on A/C systems is very limited, but reading other posts by members on this board has inspired my to tackle this project myself.

First, while researching this project, I came across mention of a variable orifice (VOV (http://aircondition.com/vov/)). Can someone who has installed one explain any benefits and/or other observations (i.e., is it a worthwile upgrade)?

The term pulling a vacuum has been mentioned a couple of times in various posts. I assume this is to evacuate the system and a vacuum pump would be used. I found a reference to a pump (http://www.tooldesk.com/products/productDetail.aspx+id+1114) that looks to be reasonably priced. Can someone explain the vacuum procedure and how to use this tool? Where would this step fit in my overall project of having my A/C produce cold air again?

Is there a general troubleshooting flow diagram that I can use to provide more information to the membership?

So, where do I start?:)

Reference Posts:
Burb w/ AC Trouble (http://www.dieselplace.com/forum/showthread.php?t=37399)
Don't get scammed by A/C shops (http://www.dieselplace.com/forum/showthread.php?t=36450)
Back for more a/c ideas (http://www.dieselplace.com/forum/showthread.php?t=37135)
Problem? My A/C is too cold (http://www.dieselplace.com/forum/showthread.php?t=37180)
A/C Help Needed (http://www.dieselplace.com/forum/showthread.php?t=36071)
A/C? (http://www.dieselplace.com/forum/showthread.php?t=34828)

I'd jump the low pressure cycling switch connector located on the reciever/dryer. This will cycle the compressor and then you can measure low side pressure before the compressor to get an idea of how much coolant is present (high side too if you have a manifold set).

I checked the codes today to see if I had missed anything and found P0251 (injection metering valve malfunction) stored in memory. I researched this a little and came across this thread:

96 Sub stalling, tried all of the usual (http://www.dieselplace.com/forum/showthread.php?t=11206)

I am beginning to think the two issues are related. I am going to examine the wiring for any signs of wear and see if there is anything happening with the ECU in the glovebox. I will also double check my filters, lift pump output and install a clear line in the fuel return line. I use FPPF Total Power regularly. I have not had the timing checked in a while so perhaps I will have to take it into the dealer. Any suggestions?