99 Caravan AC not cooling

The AC was not working on my 1999 Grand Caravan. I have replaced the compressor and recharged the system but the AC air temperature is only cooling to 60 degrees and the compressor is staying on all of the time. Any ideas on what to check?

I Would put a pressure gauge on the suction or low pressure side (the fat or larger line) and take a reading, you should see about 34psi. On my '96 I can see right at +40 degrees "F" at the center vent with the system in ambient or recirculating mode and at idle (she may drop to about +38 degrees "F" above 1500 RPM.

Forgot to add when you replace the compressor and recharged the system did you vacuum the system out for about 30 minutes prior to recharging?

I did vacuum out the system for over an hour. Our outside air temp is 88 degrees with moderate humidity. After 15 mins of idle the low side pressure is 40 psi and the high side pressure is 200 psi. After 15 minutes of high idle (1500rpm) the low side drops to 34 psi and the high side increases to 235 psi. The manufacturers sticker under the hood shows this dual unit should have 2.88 lbs of freon. I calculated this to be about 46.08 oz so I put in 44 oz of freon and 12 oz of compressor oil. I replaced the compressor and dryer with new ones and do not have any leaks that I can find. The compressor is not cycling on/off at all and the air from the ac is now staying around 66 degrees. I'm stumped! Any suggestions would be appreciated!

I think we need some more details to help you out any more.

Like bear said, Did you pull a vacuum on the system prior to charging? What were the low/high side pressures at 1500 RPM at what ambient temperature? How did you measure the amount of refrigerant you put back in?

Is your van equipped with rear A/C? If so, I belive the refrigerant capacity is 3 lbs. I recharged mine last weekend, and it was a little tricky getting the last 6 ounces to flow into the system - had to rev the engine to drop the low side pressure enough for it to flow in. Obviously, this requires you to measure by weight the refrigerant you're adding. If you just ran the engine while assuming that all the refrigerant in your can was flowing in, you may not have fully charged the system.

As a data point, prior to my recharge, my front vent temps were 61°F, rears were only about two degrees cooler than ambient (of about 86°F), Low/High side pressures were about 41/250psi @ 1000RPM. I then put in the necessary 3 Lbs of refrigerant (by weighing the charge while I was charging) and my vent temps went down to 35°F in front and 41°F in the rear, with low/high side pressures of 35/325psi at 1500RPM and 80°F ambient. What a relief to have that fixed. Cooling is now superb, and the kids no longer have red cheeks when driving around.

Given my initial symptoms of poor cooling, which I thought were entirely in the rear, my concern was a potentially clogged expansion valve, but it turned out to simply be a lack of refrigerant. I put in some dye so I can detect any future leaks as well.

See here (http://www.autoacforum.com/) for more specialized answers to your questions. They set me straight as far as needing to know how much refrigerant is in the system as a baseline for starting the diagnosis.

On edit: I apparently wrote this while you were writing your response - sounds like you do not have rear air, according to your refrigerant capacity. Your high side pressures are definitely low. My question remains, how did you measure the 44 oz of refrigerant that you put back in? Like I said, you may need to rev the engine to drop the low side pressure enough to get the last couple of ounces to go in. At least I did on mine.

Also, did you use one of those venturi vacuum pumps (the ones that hook to an air compressor)? I've never used one, but the pros that I've talked to who had actual micron gauges (1 micron = 0.001mm Hg) said these venturi pumps could not pull a sufficient vacuum and that a dedicated vacuum pump really is needed - but something is better than nothing of course.

Have you tried resetting the control panel? Could be it is mixing in a little heat because of improper calibation.
Just a thought.
Ron

The van does have dual A/C and the sticker calls for 2.88lbs of freon. My measurements are based on 4 cans at 11 fluid oz per can. The system was vaccumed with a dedicated pump and I have reset the inside control. It acts like it is still a little low on freon but I am not sure how high I can go on the high side pressure. Any Idea's Thanks

My measurements are based on 4 cans at 11 fluid oz per can
This may sound like a dumb question, but your certain they were completely empty when you were "done"? Presumably, when you released the can tap, you didn't have significant burst of "stuff" coming out?

The system was vaccumed with a dedicated pump
Is this one of those venturi style pumps that hooks up to your air compressor, or a separate self contained unit?

I'm not tryint to critisize your methods - I'm new at this as well, and attempting to get a feel for where things can go wrong when not done exactly as the pro would do it, but more importantly, how much of an effect it can have.

You keep saying "dual A/C" - are you referring to the fact that you have driver/passenger side control, or that you have front/rear A/C? I thought "dual controls" meant driver/passenger side control. Also, in my service manual, 3.0 Lbs is if you have rear air, and I think 2.88 Lbs for if you do not.

The van does have front & rear A/C and the sticker does say 2.88 lbs for a dual unit. I think it could use a little more freon I know that I am close and all cans were empty when I removed them. I am just not sure how high I can run the high pressure side without blowing the seals.

According to the Arizona Mobil Air Conditioning website the 134a low pressure reading at +80 to +90 ambient can run from 25-45 psi and the high side at the same temperature 165-270 psi. I personally like to see 32-34 psi on the low side for my cars.