brad-cam

I had my A/C system leak-tested and professionally evacuated and refilled with R12 last week. It passed the leak test with flying colors and now has a fresh charge of R12.

The problem is it isn't very cold. We are having a hotter day today - in the low 80's and it doesn't seem to blow cold enough. A thermometer in the
vents shows it's only about 60 degrees.

What could this be ? The compressor is running and the low-pressure switch is new - shouldn't be an issue as it has a full charge.

What part of the system is likely not operating properly ? I think the whole system is stock.

Porsche-O-Phile

Probably the expansion valve would be my guess. . .

Are you getting flow through the sight glass on the receiver / drier?

Kevin Baker

Properly charged r12 or 134a should drop ambient air temp by 20 degrees. Now if you are not running the a/c on the recirculating mode, the air will not get icy cold. It needs to cool the air, recirc, then cool it some more.

83na944

Kevin, shouldn't you expect at least a 30 degree drop?

Brad, if low 80s is a hot day, I don't know why you're worried.

Kevin Baker

Properly charged automotive a/c should yield a 20 degree drop. Now if you have the system set to recirculate the air in the cabin, the the first cool would go from 80 to 60, then from 60 to 40. Now we all know that our cars are not airtight, so there will be some loss of cooling as outside air is mixed with the recirculated air.

If you take a thermometer (the cheapo type you get from Harbor Frieght) and measure the air at the vent, with the air set to recirculate, the temp on max cold, fan set low speed, a/c compressor on, you should read 35-45 within 5 minutes keeping the engine at 1500rpm.

951Tom

Check to make sure your heater valve is closing, if not, your a/c will be fighting that along with the outside heat. How do you know all your R12 is still there? Are there any bubbles visible in the drier sight glass?

Peckster

Are the bubbles supposed to be moving or something?

Stan944

I'm not an expert around AC, but lack of vacuum leaks is not sufficient for proper operation. It's also important to check if the 'high pressure' is high enough, i.e. if the compressor works OK (e.g. the valves operate properly). In other words, there could be an internal 'dynamic' leak in the compressor. Any AC shop could check it.

Mello

Anyone with any experience changing this expansion valve?

951Tom

Yes, This would indicate a low refrigerant charge.

951Tom

On the 85.5 & later cars, it's got easy access once the fan assembly at the base of the windshield is removed.

brad-cam

After leak-testing and refilling my system with R12, he checked the sight-glass and reported it looked good. The pressures (from memory) I think were 30 psi on the low side and 220+ psi on the high side. He said it was right on where it should be. I'm assuming that all the R12 is still in there as it's only been a couple of weeks and he reported it leak-free. It held 30 in-Hg of vacuum for 15 minutes with no drop.

I'll check my heater valve. I checked the heater clip, the one I always hear breaks and lets hot air in the cabin - it is fine.

Sounds like maybe the expansion valve is the culprit. I'll keep checking things and let y'all know what I find.

sm

-Open the hood and lift up the rubber seal (on the fire wall) that holds the plastic cover down.
-Remove the 6 screws that hold the blower assembly down.
-Pull up on the blower assembly, which will be held down with some kind of adhesive. Pry up on one of the edges CAREFULLY.
-The Expansion Valve is on the passenger side of the car, wrapped in Presstite (sp?) black insulation tape.
-Be real careful loosening the compression nuts that connect to the expansion valve. (Tip - you do not have to turn the Ex. valve. Only turn the compression nuts (silver) connected to the pipes leading to the valve).

Make sure you have the correct Ex. valve before you rip everything apart. I didn't and am still trying to find the proper one.

That being said, I'm not sure if the compression valve is necessarily the culprit. Just because the system holds a vacuum does not mean it'll hold pressure. Have a set of manifold gauges hooked up to your A/C system again and check the pressures one more time.

83na944

Brad,

You realize that you can't change the expansion valve without first having the R12 removed, don't you?

Your best bet is to take it back to the guy who charged the system and ask him to diagnose the problem. If he needs to repair soemthing he can remove the R12, fix the problem, evacuate the system, replace the drier, and recharge the R12.

If the expansion valve were stuck, wouldn't you expect to see a reduced high side pressure (like 100psi)?

Did the guy replace the drier? Did he pull a vacuum on the system for an hour, then leak test it?

951Tom

These two gauge readings would indicate a faulty expansion valve:

1) low pressure: too low ; high pressure: too high

2) low pressure: too high ; high pressure: normal


15min isn't very long for a leak test in my opinion. Check and make sure both radiator fans are running. A high side of 220+ would mean you were around 100F ambient.