High pressure side never drops, even when car is off

[albaker]

My daughter has a 2004 Mazda 6 2.3L that was in an accident and was totalled. The car has been very reliable, and it was only the front end stuff, so we took it to a body shop and had them fix it. We took another daughter's car there a few years ago under similar circumstances, and we were very pleased with their repair. For the Mazda, I made it very clear that used parts could be used for everything except the condenser. When we went to pick up the car last fall, the owner realized they hadn't charged the a/c system, and they put 2 cans of refrigerant into the system (16 ounces, and I found out it only uses 12 ounces), but she she never used it.

They did install a new radiator, but it started a slight leak after the repair that required it to be replaced. In the process, I noticed the ugly, dirty condenser and was pretty angry. I did replace the condenser with the radiator and put in the required amount of PAAG oil for replacing the condenser. I didn't replace the expansion valve.

Given the initial repair was last fall and my repair was about a month ago, she's not used the a/c until recently (after the condenser replacement), but what I noticed during charging was that the high side never drops below around 140 psi even when sitting overnight, while the low pressure sits at 40 psi. The system never equalizes. The high side does go higher and the low side lower when the system is engaged, but it's not cooling hardly at all.

I asked a friend who does home a/c, and though he thought it was odd, he said maybe it was designed that way. I've continued to monitor the pressure several times, because it just doesn't make sense to me and my daughter is complaining about the heat. I need to do something to repair this, and I really feel the pressures should equalize fairly quickly.

Does anyone have any suggestions as to what I need to do, beside rip out the old and replace everything? Thanks

[JohnHere]

My daughter has a 2004 Mazda 6 2.3L that was in an accident and was totalled. The car has been very reliable, and it was only the front end stuff, so we took it to a body shop and had them fix it. We took another daughter's car there a few years ago under similar circumstances, and we were very pleased with their repair. For the Mazda, I made it very clear that used parts could be used for everything except the condenser. When we went to pick up the car last fall, the owner realized they hadn't charged the a/c system, and they put 2 cans of refrigerant into the system (16 ounces, and I found out it only uses 12 ounces), but she she never used it.

Great that you were able to have the car repaired!

According to the specifications I have, the A/C system for your Mazda takes 17.6 ounces net weight of R-134a, and 5.0 fluid ounces of PAG-46.

Each of the small 12-ounce cans holds about 10.5 to 11 ounces of refrigerant (depending on how much they're filled or over-filled, which can vary by manufacturer). So if the body shop added two full cans, the math says that the total amount could be over specification by a minimum of 3.4 ounces, to 4.4 ounces or more.

Hopefully, the shop pulled a vacuum on the system, it held vacuum, and they charged the system by weight into the well-held vacuum. You replaced the condenser, added PAG oil to it (hopefully, not too much—about 1.5 fluid ounces), and also replaced the R/D at the same time because the condenser and R/D are integral parts.

Because your car holds so little refrigerant and is so sensitive to the refrigerant amount, it's possible that the problem is being caused by an over-charge.

Another possibility is a clogged TXV. If the desiccant bag inside the old R/D broke open, you could have desiccant beads now clogging the TXV, which could cause the pressures not to equalize.

What were the actual pressures that you measured, and at what ambient temperature? And how many miles has this car logged?