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?

[albaker]

Thanks for your response.

I'm pretty sure the system was not evacuated during the initial recharge. Not 100% sure about this, but we were ready to leave with the car, and the owner comes running out that it hadn't been charged. They took it out to the shop, and I saw them dump 2 full cans into the system.

I evacuated the system before I recharged it, and the part I purchased claimed to have the R/D already in it. I did measure the refrigerant by weight.

Regarding the amount of PAG oil I put in, I don't recall the exact amount, but it was in the neighborhood of 1.25-1.5 ounces. I did get it from the manual.

When it was 82 degrees outside, the high side was 155 psi and the low was 42 psi. I was just going through some photos and saw that the system initially equalized while compressor wasn't running - there are photos with the high and low side exactly the same at approximately 90-95 psi. My daughter had her car at work all weekend, so I didn't get a chance to check the pressures this weekend. She's off today, so I'll check it when I get off work.

[JohnHere]

I evacuated the system before I recharged it, and the part I purchased claimed to have the R/D already in it. I did measure the refrigerant by weight.
Regarding the amount of PAG oil I put in, I don't recall the exact amount, but it was in the neighborhood of 1.25-1.5 ounces. I did get it from the manual.

You recharged the system correctly and added PAG oil appropriately.

When the condenser and R/D are integral, the claim is correct in that it will contain a new desiccant element. But it never hurts to double-check that it's actually there. Trust but verify, as the saying goes.

When it was 82 degrees outside, the high side was 155 psi and the low was 42 psi. I was just going through some photos and saw that the system initially equalized while compressor wasn't running - there are photos with the high and low side exactly the same at approximately 90-95 psi. My daughter had her car at work all weekend, so I didn't get a chance to check the pressures this weekend. She's off today, so I'll check it when I get off work.

At that ambient, the high side seems low, and the low side seems high. The equalization pressures seem high as well. Does it cool sufficiently at those pressures?

Presuming you recharged with the correct amount of pure refrigerant (containing no stop-leak or other additives) and released any refrigerant remaining in the hoses into the low side, the pressures should be checked under the following conditions:
A/C set to Max or Recirc, compressor engaged, airflow set to Dash Vents, doors and windows open (to maximize the heat load), and engine RPM set to about 1,800.
If not, recheck the pressures and center vent temperature when you get home and re-post same.

At an ambient of ~82°F, look for a center vent temperature of ~40°F or a bit lower.

Not something that's often thought about, but to be aware of:
Every time you connect a Manifold Gauge Set (MGS) to check pressures, you lose a little refrigerant to the MGS depending on hose length. Done often enough, the amount of refrigerant could drop below the minimum level, resulting in a noticeable reduction of cooling performance.