A/C overcharge?

[Roadking]

Hi All!
I just had the A/C repaired on my 97 Explorer, after not working for a year what a treat. They replaced the leaking accumulator and refilled the system. It seems to be working just O.K. the air is cool, but not cold. I was looking over my bill and I was charged for 36oz. of r134a and under the hood the sticker specifies 30oz. of refrigerant. The mechanic said anything between 30oz. and 40oz. is fine, 36oz. should be perfect. Would a system that was over charged not cool as well? What do you think?

 

[budwich]

Interesting.... you get alot of A/C guys saying that the "only way" to go is to have the system evaced and the "exact" amount put in (repaired components of course). From this "take", it would appear that the "exact amount" is almost anything that an A/C guy wants to put in and charge you for... I too am intersted in more discussion and opinion on this as I have been wrestling with the "Walmart kit" and seeing the "A/C suicide" comments in most discussions. I guess I have the "What gives???"

 

[Glacier991]

In a stock system, there is an amount of refrigerant which is sufficient to handle most all variations of the system needs adequately. Neither starving the evaporator in the worst case, nor flooding it either. That is the factory recommended charge. On conversions this was an issue because on a conversion from R-12 to R-134 you actually need LESS 134 than you used to use R-12. On a factory 134 system, you go by the sticker. I disagree with your AC guy that 30 to 40 is fine. An overcharge WILL affect cooling performance, enough of an overcharge can try and make it's way back to the compressor not as a compressible gas, but as a non-compressible liquid. Compressor damage can result. A flooded evaporator is not cooling optimally as it is not allowing the change of state from a liquid to a gas to be fully realized (the so-called "latent heat of vaporization"). I'd guess this could cause a loss of cooling of between 5 to 12 degrees at the vent.

Is the extra 6 oz the cause of your poor cooling performance ? I cannot say with any certainty, but your optimal refrigerant load is what the sticker says, not upwards of 33% MORE. I suspect your mechanic is not real well versed in AC issues, and just knows the basics of how to remove and replace components and refrigerant.

 

[Roadking]

Thanks for the advice.
I’ve got access to a set of 134 gauges that I used for filling my leaky system in the past. Is there an r134a chart that calculates what pressures I should have a set temperatures? If so, would it be possible to check the system myself and see if I’m in the ballpark?