Automotive Air Conditioning Information Forum

"The higher "warm superheat" setting likely keeps evaporator pressure down to pretty low values enough to still give appreciable cooling at idle, even with such a tiny and basically not so strong at idle comp (an issue peculiar to rotary compressors). Once you get the car moving, the suction down due to a comp that is spinning way faster and the condenser cool due to a better airflow, the evaporator temp drops and the TXV drops the superheat down in order to prevent evaporation pressure from falling down too fast."

So, my AC is probably fine, it just can't compete with 97 degrees, 50% humidity, and slow traffic?

tbirdtbird wrote: Sat Jul 03, 2021 9:53 am Static pressures ( AC system off) should be equal not sure what is up with that.
Other pressures seem lower than they should be.
Maybe the charge capacity that John Here came up with is closer to being correct,
I agree it seems low on charge

Yes, the static pressure was concerning.
I agree on the low charge.
Should I try to add more refrigerant? Maybe an ounce at a time?

It should; and BTW superheat and subcooling are parameters used in residential and commercial but not in MVAC.
See my reply above and wait for the mods, they are the supertechs

Right now patience is a virtue, we don't want to harm the system....
Look at the list of mods, and wait for one of those names to show up, I have a lot of respect for those 4 guys

tbirdtbird wrote: Sat Jul 03, 2021 10:03 am It should; and BTW superheat and subcooling are parameters used in residential and commercial but not in MVAC.
See my reply above and wait for the mods, they are the supertechs

Right now patience is a virtue, we don't want to harm the system....
Look at the list of mods, and wait for one of those names to show up, I have a lot of respect for those 4 guys

Great. Thank you.

If you're just guessing at refrigerant levels by pressure, using the magic green dial. Go ahead and play all day with refrigerant levels.

The proper way is to reclaim the refrigerant and do a proper charge procedure (Real Guage Set) to OEM specs. Then if there is an issue, we can chat.

Tim wrote: Sat Jul 03, 2021 10:08 am If you're just guessing at refrigerant levels by pressure, using the magic green dial. Go ahead and play all day with refrigerant levels.

The proper way is to reclaim the refrigerant and do a proper charge procedure (Real Guage Set) to OEM specs. Then if there is an issue, we can chat.

It was originally charged by weight according to the hood sticker.

Well, it turns out my belt is slipping. It was making a hissing noise, rather than a squeal, so I didn't notice. I sprayed some belt dressing on it and it started hissing louder, then quieted back down. That might also explain my intermittent low alternator voltage. If that was the problem all along, I'm going to be happy and angry lol.

Honestly belt dressing should be avoided, it is not the answer.
A new belt is, and they are not that hard to install.

Be sure to check the tensioner pulley, which is spring loaded. The bearing will often gum up and make it hard to turn, in some cases locking the bearing totally. It must spin freely, else change that too

tbirdtbird wrote: Sat Jul 03, 2021 11:29 am Honestly belt dressing should be avoided, it is not the answer.
A new belt is, and they are not that hard to install.

Be sure to check the tensioner pulley, which is spring loaded. The bearing will often gum up and make it hard to turn, in some cases locking the bearing totally. It must spin freely, else change that too

Yes, I agree. It was just a diagnostic experiment. I'm going to get a new belt and tensioner/pully if need be soon.

Other than the unusual static pressures already called out, IMHO the running pressures are just about what they should be at an 80-degree ambient, except that the low pressures at idle are slightly elevated. But the idle speed should automatically bump up a couple hundred RPM whenever the A/C is turned on, lowering those pressures (and vent temps) a bit and helping with cooling when stopped at, say, a traffic light. Do you notice an increase in idle speed when turning the A/C system on? If not, that could be something else to investigate.

The low pressures of 22-25 PSI at 1,800 RPM translate to an evaporator temperature of about 25 to 29 degrees which, by the time the evaporator air reaches the dash, should result in vent temps of around 38 to 40 degrees. Are you sure there's no heated air mixing with the cooled air somehow?