A/C Diagnostic and Troubleshooting - Help Needed
 

I am trying to tackle the job of repairing my A/C system in my 2002 Ford Windstar. Here is the information I have gathered so far:

1st Scenario - Pressure Test with engine off, nothing running:

Low side pressure - 70psi
High side pressure - 70psi

2nd scenario - I then started the engine, rolled windows down, set rpms at about 1800, and turned A/C on full blast and let run for 5-10 minutes. Here are my readings:

Ambient Temp - 70f
Vent Temp - 68f
Low side pressure - slowly creeps up to 40psi, then compressor kicks on at 40 (for only one second) and pressure drops instantly to 20psi and compressor kicks back off
High side pressure - stayed around 140psi, then shot up to about 150psi when compressor kicked on (again, only for a second) then back down to 140psi when compressor kicks off

Note that the compressor only kicked on once every 10-15 seconds for only 1 or 2 seconds max

3rd Scenario - I "jumped" the low pressure switch forcing the compressor on and let run same as scenario 2 for about 10 mins, here are the readings:

Ambient Temp - 70f
Vent Temp - 70f
Low side pressure - negative 10psi
High side pressure - 210psi

My understanding is that if low side goes negative and high side is high, then the problem is a clogged evaporator core and possibly clogged expansion valve as well. Can anyone confirm this?

Also, this van had rear A/C. Does it have a seperate rear evaporator core and expansion valve?

Any information would be greatly appreciated.

Thanks,

Nick

Im by no means a a/c expert ,there are more qualified members than I, to start you sytem has a accumlator / drier and a orfice tube aka expansion tube .sounds like your headed in the right direction either low freon or a restriction.If you had access to a a/c machine you could pull out the freon and measure it to see if its low but you probably dont.There is a rear evaporator but I think only one orfice tube.Is the compressor noisey or original with alot of miles ? they only last so long before they start to come apart and will plug up the system.also dont run your compressor to long by jumping it or you will have failure its cut off for a reason.normally if your compressor was running you can also spot a restriction by a frozen spot on one of the lines,just a little info will try to dig more maybe someone else can chime in.

Windstar03 gave you some good advice.
If anyone has added refrigerant to the system they may have introduced moisture to the system which can cause a few problems.
You will need to open the system, but we are not supposed to suggest you violate the law by allowing the refrigerant to escape into the atmosphere.
You will need to plan on replacing at the very least, the dryer assy which is part of the accumulator assy the orifice tube, and whatever you find that is not normal and that can be black junk trapped in the orifice tube. Sometimes the dryer sack lets go and plugs the orifice. It does sound like you have at least the gauges, but you may need to flush the system, possibly replace the compressor, replace the orifice tube , the accumulator, add the correct type and amount of refrigerant oil, install a line filter , evacuate the system with a vacuum pump just for that purpose, and recharge the system with the correct amount of refrigerant. I don't know if you want to get involved with this since it does require some special tools and procedures. Not to discourage you, but it can get expensive if not done correctly.