Leave well enough alone or charge AC system? Older Hondas

[GJHANS]

I've read through a number of the posts in the Auto Air Conditioning Procedures forum.

I would like to be proactive and help keep the AC in good working by maintaining the recommended amount refrigerant in the following two vehicles.

2005 Honda CR-V
Compressor, condenser and condenser fan and R134a replaced 8 years ago. R134a recharged 3 years ago. AC blows cold. This generation CR-V is known to have problematic AC system. The compressor has already been replaced at least twice over the years. The AC system rehabs are expensive, so I'd rather evacuate and recharge or recharge the system every 3 years or so if it will help defer expensive replacement of components.

2001 Honda Civic
Compressor, drier, AC blower motor, condenser and condenser fan and R134a replaced 6 years ago. No refrigerant has been added in 6 years. AC is cold but used to be 44 degrees coming out of the central vents last year and now seems a bit higher, maybe 46 degrees.

My concern is that each year the system loses R134 and my understanding is that when the refrigerant gets low the AC system components' life expectancy is reduced.

Some options for me might be:

1. As long as the AC blows cold and the compressor doesn't cycle on and off, just leave well enough alone and as is.

2. Buy or borrow an accurate set of manifold gauges and use the temperature/humidity/ low & high pressure charts to determine whether or not the system is within specification.

3. If low on refrigerant, add R134a until the low high pressure are within the correct range.

4. If low on refrigerant, properly evacuate the system to 29'' and hold the vacuum for an hour or so. Then, using an accurate scale to determine the amount of refrigerant used, add the recommended amount of ounces of R134a.

I would like to get your opinions on how to best proceed to get the maximum life out of the AC system.

Thank you very much appreciate your expertise.

[JohnHere]

Generally, seasonal refrigerant losses will occur over time, usually from seepage through the compressor-shaft seal. My main concern is operating an MVAC system with a lower-than-optimal refrigerant charge, which will cause the compressor to run with less oil, risking internal damage or even complete destruction.

That said, if the system is cooling as it should, I would indeed leave it alone per your Item #1. However, if you begin to notice warmer air emanating from the vents or the evaporator icing-up and blocking airflow through the vents, the system is most likely low on refrigerant. It doesn't take much for these troubles to occur—only an ounce or two loss will start to affect cooling performance, especially in cars with a small refrigerant capacity, like yours. Use an accurate thermometer (I prefer the digital type) placed into one of the center vents to measure the air temperature, which will fluctuate depending on vehicle settings and operating conditions.

A Manifold Gauge Set (MGS) used to monitor the high-side and low-side pressures can't tell you how much refrigerant is currently in a system, though. The ONLY WAY to determine that is to recover the refrigerant charge using an expensive Recover, Recycle, Recharge (RRR) machine that usually only professional A/C shops have. The machine will tell the operator how much refrigerant (net weight) comes out, along with any oil (fluid ounces) that is recovered. The RRR machine "gauges" how much of each it recovers so that you'll know whether the system was low on refrigerant, or conversely, overcharged.

Once the system is completely empty of refrigerant, then proceed to your Item #4, presuming that no system repairs and/or component replacements are needed beforehand.

[GJHANS]

I should also have mentioned the cabin air filter has been maintained.

I found the following on the internet, regarding a "rough test of the AC system would be to turn the fan on low, set the temp at minimum, set the vent to fresh air, run the engine rpm at around 2500. Measure the ambient temp and then measure the center vent temperature. You should see approx a 30-40 degree temperature difference between the ambient and vent temperatures."

Would the above be a reasonable way to test AC performance or is there a better way to get an idea if the AC is working properly in these old Hondas?

Thanks

[GJHANS]

The machine will tell the operator how much refrigerant (net weight) comes out, along with any oil (fluid ounces) that is recovered. The RRR machine "gauges" how much of each it recovers so that you'll know whether the system was low on refrigerant, or conversely, overcharged.

Thanks for your reply and the info re the oil. I had assumed that when the AC is evacuated, the oil would stay in the system and only the refrigerant is removed. I am curious as to how an AC shop with the RRR machine determines the correct amount of refrigerant to add. Also, when an AC system loses an ounce (or several) of refrigerant over time, doesn't some of the oil also escape?

Thanks again!

[JohnHere]

I should also have mentioned the cabin air filter has been maintained.

Excellent.

I found the following on the internet, regarding a "rough test of the AC system would be to turn the fan on low, set the temp at minimum, set the vent to fresh air, run the engine rpm at around 2500. Measure the ambient temp and then measure the center vent temperature. You should see approx a 30-40 degree temperature difference between the ambient and vent temperatures."
Would the above be a reasonable way to test AC performance or is there a better way to get an idea if the AC is working properly in these old Hondas?

I modified the statement you quoted as follows: "rough test of the AC system would be to turn the fan on low (high), set the temp at minimum (good), set the vent to fresh air (good), run the engine (and compressor at least 90 seconds to stabilize the system), rpm at around 2500 (~1,800). Measure the ambient temp (directly in front of the grille), and then measure the center vent temperature (good). You should see approx a 30-40 degree temperature difference between the ambient and vent temperatures (good, but not necessarily under normal operating conditions)." Also, doors/windows should be open to maximize heat load on the system.

[JohnHere]

I had assumed that when the AC is evacuated, the oil would stay in the system and only the refrigerant is removed.

The oil will stay in the system during evacuation prior to recharging. During recovery of the refrigerant using an RRR machine, some oil usually comes out. It accumulates in a graduated vessel attached to the machine so that the operator knows how much oil to add back in.

I am curious as to how an AC shop with the RRR machine determines the correct amount of refrigerant to add.

There is a database (updated regularly) that the manufacturer of the machine provides to the machine owner that specifies how much oil and refrigerant to install. The operator looks up the specs on the machine, and they appear on a screen attached to the machine. If you have an under-hood decal with specs that differ, the rule is to always go by the car manufacturer's decal.

The specs that I have for your cars indicate the following:
For the 2001 Civic: 23 ounces net weight of R-134a; 5.0 fluid ounces of PAG-46 oil.
For the 2005 CR-V: 18 ounces net weight of R-134a; 4.5 fluid ounces of PAG-46 oil.

Also, when an AC system loses an ounce (or several) of refrigerant over time, doesn't some of the oil also escape?

It usually does, but the amount is minimal with a minor leak or leaks.

[Cusser]

That said, if the system is cooling as it should, I would indeed leave it alone per your Item #1.

Exactly what I would do.

[GJHANS]

That said, if the system is cooling as it should, I would indeed leave it alone per your Item #1.

Exactly what I would do.

Thank you, that makes sense....my main concern was that when the refrigerant charge gets too low (and if I don't catch it in time) it might cause expensive damage. That's why I considered doing a preemptive evacuation and recharge. The consensus appears to be that it's better to wait until no longer cooling sufficiently and then have it recharged.

I appreciate the expertise on this forum. It's been a great help.

[JohnHere]

20210825_105437.jpg (247.91 KiB) Viewed 181 times

Place a thermometer in the center vent and keep it there so that you can monitor A/C performance as you drive. Should temperatures rise into the uncomfortable range, you'll know immediately that you have a problem, verified by the thermometer.