Too Much A/C Refrigerant?
 

Hi, The A/C in my 97 Expy with rear climate has been slowly over the past year or so hasn't been cooling that well. I've always done 95% of my own vehicle work, so i figured this was a good time to learn about A/C. I bought a set of gauges, read a lot of posts and tested first. Yes I realize there's a slow leak that should be fixed first, but if it'll hold through the summer, I can deal with it when it's cooler out.

The high side pressure never went over 150, but the compressor did cycle. So I put a can of refrigerant into it the other evening (80 deg ambient temp), and the high side pressure was up to about 195. The low side cycled between about 22 and 45psi and turned the compressor on and off, just as the manual says. Cooling is still not that good though. I've dug through the factory manual and all it says is that 3lbs 10oz is the correct charge. It doesn't say anything about correct pressures.

So can anyone tell me what the correct high side pressures are for this system? Should I add another 12 oz can of refirgerant? If I can't tell how much weight is in the system, is there any other way to tell if there's too much?

Oh, and I thought I should add a couple of ounces more oil too so I bought some, but then I realized it was oil plus this ICE 32 stuff, some friction reducer. Will ICE32 harm the system? I'm not a fan of that kind of thing.

High side should be 200 PSI minimum at idle and low around 35 PSI.

Regardless of anything you read or hear, the compressor is not supposed to cycle on and off. Cooling is achieved only through the act of the compressor running. This is not to be confused with the cycling switch that will shut the compressor down if it senses the condenser is freezing up. That's different from the low pressure cut out switch. People often confuse the two as being the same thing.

Well I should have said at idle it does not cycle, the compressor runs all the time. If I keep the rpms at 2000, then it cycles, but its like 3 seconds off, 15 sec to constant on.


So the high side pressure should not go below 200 when the A/C is running? Is that dependent on ambient temp? It's in the mid 90s here in the East this week.

That's right. Ford's charging instructions are to charge a weighed amount into a clean and vacuumed system.


Typical high side pressures should be between 2.0 and 2.5 times the ambient temperature in degrees F.

Then you're still low, add another can. The compressor should be running as long as the system is in A/C mode. The more it cycles on and off, the more it stresses the drive belt and wears down the clutch surfaces.

I have a 2002 excursion and the rear ac wasnt cooling very well.. changed the expansion valve in rear compartment and changed the orfice tube... pulled a vacuum on system and now it works great..u should have a tag under the hood that tells u how much freon your system holds.good luck.

Great, thanks for the help. I'll add another can tonight and see what happens. Plus I found a 2oz oil charge, minus the ICE32 stuff. I'll put that in too.

The only thing I've noticed that seemed odd was that when the rear AC is on, the front AC gets a little cooler. Turn the rear off and the front gets a bit warmer. Is this normal?

I found the page below when I was trying to tune up the dual system on my 03.

http://www.justanswer.com/questions/...003-expedition

I put another can in it last night. This morning's drive to work, about 20 mins, I ran it full blast max the whole way, both front and rear running, testing with an IR thermometer.

At idle, it blows in the 50s. Around town driving averaged in the 30s, sometimes low 40s. At highway speeds saw mid 20s to low 30s much of the time, and once it briefly dipped to 17! Abient temp was 78. The inside temp of the car got to about 57. I hoped I could get it to blow a little cooler for vaca next week, but I wasn't expecting the car to become a freezer. ;)

When i got to work, I had to get some hot tea.

Test it in the heat of the afternoon before you claim victory. Any half-assed-operating system can freeze you out in mild conditions but will fail you when conditions get hot.

30-40 degrees out of the vents when it's nearly 80 out is a pretty good indication that the system is working properly.

Agreed. It ain't bad. It's just a "sure" test.

Yep, and for sure this is a great week to test any A/C system.

It's 90 this morning, and the front AC alone was plenty cool, but I didn't measure it. It's supposed to go to 102 today. I'll put the thermometer on it when I go out at lunch and post the results.

10 mins of stop and go driving under 35 mph, and the AC temp slowly dropped to mid to high 30s in the coldest vent, low 40s in the others. Stopped, it rose to 50-60. But 60 doesn't feel bad when the inside of the car is 130. I'll take it.