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AC pressure question

70monte on Wed September 03, 2008 6:34 PM User is offline

Year: 2005
Make: Pontiac
Model: Grand Prix
Engine Size: 3800
Refrigerant Type: R-134a
Country of Origin: United States

Tomorrow I'm going to be recharging the AC in a friend's 2005 Grand Prix. He had to replace an AC line due to a previous accident. Can anyone tell me what high and low pressures I should see on this car?

Is there a book or a source where I can find out what the normal range of pressures are for the newer cars? My AC book that I have only goes up to 1998. Thanks.

Wayne

Chick on Wed September 03, 2008 7:01 PM User is offlineView users profile

This is the simple part of using factory refrigerant. There is a tag under the hood with the amount for the system.. Pull a deep vacuum (don't know if you flushed, or lost oil, if so replace it) then charge the system amount back into the system..Use the pressures to check after the system is full. They will vary from car to car, if you'd like, post the pressures here after it's filled along with the outside temp and we can take a look at it..If you fill it and it doesn't cool, same thing, post the pressures...Hope this helps..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

70monte on Wed September 03, 2008 7:46 PM User is offline

Chick,
thanks for the response. The system has not been flushed and the owner said he doesn't think there was any oil loss so basically all he wants done is for me to pull a vacuum and recharge. the car holds 2.3lbs of R134. I told him he probably should change out the Accumulator since he had the system open for about 35 minutes while he changed out the line but he really doesn't want to spend the money since he is going to be selling the car. So, I don't know how successful this will end up being. Tomorrow the ambient temp is probably only going to be around 65 F since it is supposed to be raining all day just like today.

Another quick question. In the Pressure-temperature relationship chart in the Mastercoo service manual, does the Evap temp refer to the temperature of the air coming out of the middle vents or is this something else? Is this the chart to use to figure out if the pressures I'm going to be seeing are normal?

I doubt I will be able to post pressures during the repair since the computer doesn't work too well at the house I'm doing the repair at. Thanks again

Wayne

Chick on Wed September 03, 2008 8:08 PM User is offlineView users profile

Just jot them down along with the ambient temp, it should be pretty straight forward. The reason I hesitate to give you the pressures are that they are at the very least generic.. look for a low side of around 30 to 40psi, and high side can range anywhere from 160 to 200 depending on the fan being on, and of course ambient temp.. So it's always best to fill by the sticker amount, use the pressures to check that the system is operating, should you have a cooling problem. Suction line should be cold right back to the compressor if everything is working properly. No need to change the accumulator, although it's always the cheapest insurance.. let us know how it turns out.. (if it cools it's working..)

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

70monte on Wed September 03, 2008 8:31 PM User is offline

Chick,
Thanks again. I will let you know how it turns out. Just for my own knowledge and curiosity, does the Evap temp in the Mastercool service manual in regards to pressure/temperature relationship chart refer to the temp of the air coming out of the center vents in the dash? Also, is this chart used to get a general idea of normal AC pressures? Thanks for all of your help.

Wayne

Chick on Wed September 03, 2008 9:40 PM User is offlineView users profile

I don't have that manual, but no, it doesn't mean anything about vent temps, I'd have to read it to be sure though..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

70monte on Fri September 05, 2008 12:16 AM User is offline

Well, I finally got the 2005 Grand Prix's AC charged but not without a few stupid moments on my part. I hooked the gauges and vacuum pump up to the car and started to pull a vacuum. The needle on the low side didn't move at all. I let it run for about 10 min and no changes. I asked the guy if he had changed out the O-rings on the line he had replaced and he said no. So I figured we had a leak there. We took the line apart and replaced the O-rings and washers. I then started pulling a vacuum again with no results. I have a Robinair #15600 6cfm pump. I started looking at the trouble shooting section for the pump. After reading, I realized I had forgot to turn the Iso valve to the open position. I had the valve side of the pump facing away from me and had forgot all about it. Boy did I feel dumb.

The vacuum process then proceeded like it should. I let it sit after vacuuming for awhile and the gauge held steady at 29. I then started the recharging process.

Here is where I made the next two mistakes. I forgot to purge the line going from the can to the manifold twice so I did let a little bit of air into the system.

I put in three 12oz cans and an ounce from the can that was already on my can tap for 37oz. Ambient temp in the garage was 70 F. During the recharging process the low side held at 30 and the high kept going from about 170 back to about 115 and it did this for awhile until it stabilized. It took awhile for the vent temps to come down. They stayed at 59 F for awhile. After the last can went in the vent temps went down to 45 F and final pressures were 35 low side and 245 high side.

We then took the car for a drive and the vent temps went down to about 39-40 F which he and I felt were good.

The low side pressure seemed normal but the high side seemed a little high for the ambient temp but it may be from the little bit of air I let in.

Hopefully when I do my 92 Cavalier, I won't make these same mistakes again.

Wayne

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