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What do you think? Do I need to add refrigerant?

dcmeigs on Fri May 27, 2011 5:22 PM User is offline

Year: 1991
Make: Ford Taurus
Model: SHO
Engine Size: 3.0 L
Refrigerant Type: 134a
Ambient Temp: 95
Pressure Low: 40
Pressure High: 177
Country of Origin: United States

The A/C doesn't seem do be operating as it has in the past, and the change seems sudden. It's really hot, about 95 or 100 in the garage, and I checked the pressures and found 40 and 177psi at idle and 20 and 200psi at higher RPM. I'm getting air discharge on the road at 65 mph of about 72 degrees with a cabin temp of 87 degrees (it's a black car in Phoenix). 87 is about as cool as it will get in the cabin at 2 in the afternoon.

I guess what I'm asking is whether I should be making decisions about refrigerant pressures at idle or a higher engine speed. The chart has a range of 25 to 43 as low side readings in the 90s; 165 to 270 on the high side again in the 90s. Are these two numbers perhaps idle and operating speed?

Thanks. I appreciate the help.


Edited: Fri May 27, 2011 at 8:03 PM by dcmeigs

Dougflas on Fri May 27, 2011 8:45 PM User is offline

You should recover the charge and put the correct amount in it. If that is not an option, try adding a little at a time. I think you're low. High side should be higher, low side should be 30to 35ish. Engine rpm at 1500. Put a box window fan in front of the grill.

Cussboy on Sat May 28, 2011 11:01 AM User is offline

Originally posted by: dcmeigs
The A/C doesn't seem do be operating as it has in the past, and the change seems sudden. It's really hot, about 95 or 100 in the's a black car in Phoenix...

Dave - you have a black car, converted to R134a, in Phoenix. You could be having condenser-cooling issues, air getting in from the heater, low refrigerant, or more. Consider making an appointment at AMA in Phoenix, the board sponsor. They have a full-service facility, and I'd say you'd get more experience for your dollar there.

Adding refrigerant - without knowing how much by weight is in there - can be tricky. If you do go down that path first, I'd add just a few ounces, like half a can, like Doug posted. I did similar a few weeks ago in the 2008 Mazda CX-7 my daughter just picked up, half a can only, and it produced good results so far.

As you already know, any time refrigerant is low, there is a leak. A leak requiring 6 ounces every few years is not a huge concern, but same amount every month needs to track down the leak and fix it.

dcmeigs on Sat May 28, 2011 5:25 PM User is offline

Thanks to both of you for the advice.

I just happened to notice the AMA sponsor banner and I spoke to Jack at AMA on Friday. Unfortunately, he was booked prior to the holiday but offered some very helpful advice. (I didn't mention it in my OP because it seemed like too much information, but I initially had a problem with the climate control feeding unwanted BTUs from the heater core loop that was overpowering the A/C). You can imagine that such a failure was a difficult problem for a noob to troubleshoot. In doing so I accidentally released some refrigerant. I added a little to replace that lost, but I was not keeping the car at 1500 RPM.

I think I'll keep adding a few ounces at a time to bring the low side to 30 or 35 with the car at 1500 and see if that resolves the problem. I can take it back to AMA after the holiday for a professional service if I don't get satisfactory results.

Thanks for your help. On line forums like this one are the great unheralded virtue of the internet.


dcmeigs on Sat May 28, 2011 7:44 PM User is offline


I added just 2 oz to bring the pressures up to 35/230. I now have vent temps of 55 at highway speeds and a nice cool cabin on a 100 degree day. In the words of Everett, "I'm feeling pretty good about myself".

Thanks again for the advice.

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