I apologize if this has been covered elsewhere, but my searching didn't find anything to help me.

I rebuilt a 2007 Saturn Aura XE (3.5L) which had a lot of front end damage. Among the damaged items were both A/C lines and the condenser. After acquiring all of the parts that I needed to rebuild the car, I vacuumed down the A/C system, made sure that there were no leaks (no loss of vacuum after three hours), and charged the system with the specified amount of refrigerant (based upon weight). However, there is a delay in when the cooling kicks in (the compressor runs from the time I switch on the A/C). In moderate temperatures, it takes about three minutes before I get cold air. The hotter the outside temperature gets, the longer it takes to start cooling (sometimes as long as ten (or more) minutes. Once it kicks in, my vent temperature gets down to 38-39 degrees (F).

I'm thinking that the compressor might be wearing out. Can anyone confirm this? Would adding PAG oil make a difference? Other things I'm not considering?

 

it is possible that the new condenser is not as efficient as the previous condenser was. Did you replace it with a new one or a junkyard one? You are counting on efficient removal of heat as the refrigerant goes through your condenser and transforms from a gas back to a liquid before it circles back through the system. Something as simple as rinsing all the fins off with a garden hose can make a huge difference in available surface area to dissipate heat. The new condenser may also simply not have the heat dissipation efficiency that the old one did. Basically the system is not operating as efficiently as it could or as designed. If it eventually reaches temperature, that would be my guess.

 

Don't blast it with a concentrated stream of water or a power washer. You will bend and destroy the fins and probably soak the auxiliary fan motor which is never good. They make spray cleaners for AC condensers for home units. I suppose they make them for automotive condensers. I would not use house stuff on the car condenser as the material may be different.

 

I decided to evacuate the system, vacuum it down (no leaks), and refill it with the specified amount of refrigerant (I also added 2 oz. of PAG Oil). Presuming that the condenser is OK (it is an OEM one). The cooling DOES start a bit sooner, but it sometimes does take up to 5 minutes before it starts to blow cool air through the vents (previously, it could take more than 10 minutes on a day with temp in the nineties). Once it starts cooling, the temperature at the center dash vent is between 38 degrees and 42 degrees, which is great.

I'm just curious as to whether this is normal operation, or not. I don't recall ever having this issue on any other car I've owned. Could the compressor be getting weak and in need of a replacement? If it is, I will probably tolerate the delay until the compressor goes out completely (or, at least, until next spring when I can better afford to replace it). Any other ideas (if the delay is not normal and indicates an issue in the system)?

 

Not picking at you.....

To what vacuum level did you pull, and how long did you let it sit to evaluate leaks?

Sometimes the compressor will leak internally, reducing the ability to efficiently compress the refrigerant.

With the AC running, what other high and low side readings on the system? You can hook up the gauge set before startup, I note the static readings, and have someone else start the vehicle and watch the high and low side pressures change as a function of time. It should be a very rapid change that stabilizes quickly. Monitoring of these pressures gives you a direct indication of the operation of the system as a whole.

Please let us know the results.

 

I don't feel as if you are picking at me - if you need information to make an informed recommendation, then I have no problem getting it to you. Unfortunately, I do not have, at the moment, any measurements since I last charged the system. And I don't have any of the previous readings. I will get them tomorrow (08/18/2025) and follow up in another message.

I pulled a vacuum down to -29. Gave it three hours to see if would lose any vacuum/had any leaks.

 

There is also the possibility that the thermal expansion valve (TXV), which regulates the flow of refrigerant to the evaporator, is not fully closing or is slow to close or is partially clogged with "debris". This would limit the rate at which refrigerant enters the evaporator, reducing the cooling efficiency.

We should be able to detect this by watching the high low pressure behaviors.

 

The THX was replaced with a new one, so I don't think there is a problem with it. And, IIRC, the last time I had the manifold gauges hooked up to it, there wasn't any indication that there was an issue with it.

Something that I just realized late last night is that the baffles which surround the condenser were damaged. I have replacements, but haven't put them on yet. However, from my understanding, this would cause the overall cooling efficiency to be reduced (i.e., instead of the max cooling temperature getting down to a normal value, it would remain several degrees higher than it should.

I think I'm just going to tolerate the delay until next spring (as long as it does eventually start cooling) and then (possibly) replace the compressor.

I do appreciate all of your input.