adding R134a to a 2002 Sienna

I went over to Wal-Mart, and I noticed the cans with a pressure gauge have a nice table printed on the can as to what the pressure should be, depending on the ambient temperature. I also noticed they sold cans without a pressure gauge (which were half the price as the ones with a gauge). How on earth would you know when to stop, without a gauge?!

I was about to buy a can with a gauge, then decided to do a little more research before committing to a can. I have to go back there to get a Father's Day gift anyway. =3D)

It might be, or it might not be. You will need to measure the pressures in the rear system and see what is going on. If you dont achieve the specified pressures, then you have either a lack of refrigerant OR you have a mechanical problem with the compressor, valves, etc.

If you know how to do it, you can buy a can of refrigerant with a pressure gauge, and you can attach it to the vacuum side of the compressor. Add refrigerant very slowly until your pressure measurement reaches the value mandated. (You can find this on your can of refrigerant or you can find it from the data for your particular application)

If you have adequate cooling, then you guessed correctly.

The more certain way is to take this beast to a competent refrigeration mechanic and avoid the mystery.

There are two ports, a High Side and a Low Side. The ports are different sizes. You cannot connect to the wrong port.

Buy a can of R134a and follow the directions for NORMAL user service of the system. For system repairs, this not gonna work, but to refresh the system, it is fine.

I went over to Wal-Mart, and I noticed the cans with a pressure gauge have a nice table printed on the can as to what the pressure should be, depending on the ambient temperature. I also noticed they sold cans without a pressure gauge (which were half the price as the ones with a gauge). How on earth would you know when to stop, without a gauge?!

+++++++++++++++++++++++++++++++ You would not know unless you already owned a pressure gauge. Buy the can with the gauge, then move the gauge to a new can next year. Honestly, you should not need a new can every year, but the point is to save the gauge and use it the next time you need another can.

Haynes sucks. Chilton's sucks. AutoZone.com sucks but is free, so try the= m. PDFtown.com has some Toyota factory manuals.

A website dedicated to car A/C:

Don't R-134A systems use different size fittings for the low and high sides= , meaning you don't have to worry about this? But to confirm, run the engi= ne at about 1500-2500 RPM with the A/C on high, and feel around the chargin= g ports. The low-side port is cold, the high-side port is hot.

You really should get an R-134A guage set and a couple of A/C or food therm= ometers and charge when the outdoor temperature is around 70F - 80F. Some = car A/C systems are really touchy about the right amount of refrigerant, so= shops will often pump out all the old gas and weigh the amount of gas they= put in.=20

DO NOT OVERCHARGE THE SYSTEM!

This is my half-arsed way of charging:

Check the accuracy of the 2 thermometers by putting them in a glass of well=

-stirred ice water while their tips touch, to verify that they read identic= ally. Tape the tip of one thermometer to the inlet pipe going to the evapo= rator coil, the other to the outlet pipe. This should be near the firewall= . Make sure the thermometer tips make good contact. Run the A/C on high a= nd idle the engine at about 1500-2000 RPM, and the temperature readings sho= uld drop. The outlet temp will be higher than the inlet if the system is u= ndercharged. Open the R-134A can's valve slightly to SLOWLY charge the sys= tem until the outlet temp is almost as cold as the inlet temp, or the press= ure readings are right, whichever comes first. Try to charge while the out= door temp. is around 70F - 80F because in hotter weather you need to underc= harge the system to prevent excessive pressure. Before connecting the hose= to the low-side charging port, open the R-134A can's valve slightly, to pu= rge the air out of the system, and don't close the valve until hose fitting= is attached.

Temperature difference between evaporator inlet and outlet pipes, emphasis = on DIFFERENCE. If you rely on pressure alone you stand a good chance of ov= ercharging the system, especially in warm weather (not that going by evapor= ator inlet/outlet temperature difference alone will spare you from that), a= nd apparently it takes only a few PSI of overcharge to hurt the cooling per= formance noticeably.

The directions probably mention always keeping the R-134A bottle upright so= that only gas gets into the A/C, not liquid, and placing the bottom half o= f the bottle in a pot of warm water (about 90F - 110F) to keep the pressure= up (bottle will otherwise get cold enough to form frost on the outside). = Make sure you have room in the engine compartment to keep the water pot up= right, even while the engine is running and shaking.

BTW buy plain R-134A, nothing containing leak detection dye or compressor o= il.

On May 26, 5:02=A0pm, snipped-for-privacy@my-deja.com wrote: ...

rmometers and charge when the outdoor temperature is around 70F - 80F. =A0S= ome car A/C systems are really touchy about the right amount of refrigerant= , so shops will often pump out all the old gas and weigh the amount of gas = they put in.

ll-stirred ice water while their tips touch, to verify that they read ident= ically. =A0Tape the tip of one thermometer to the inlet pipe going to the e= vaporator coil, the other to the outlet pipe. =A0This should be near the fi= rewall. =A0Make sure the thermometer tips make good contact. =A0Run the A/C= on high and idle the engine at about 1500-2000 RPM, and the temperature re= adings should drop. =A0The outlet temp will be higher than the inlet if the= system is undercharged. =A0Open the R-134A can's valve slightly to SLOWLY = charge the system until the outlet temp is almost as cold as the inlet temp= , or the pressure readings are right, whichever comes first. =A0Try to char= ge while the outdoor temp. is around 70F - 80F because in hotter weather yo= u need to undercharge the system to prevent excessive pressure. =A0Before c= onnecting the hose to the low-side charging port, open the R-134A can's val= ve slightly, to purge the air out of the system, and don't close the valve = until hose fitting is attached.

.....

Thanks to everyone for the advice. This is embarrassing, but I think the A/C is working properly. I didn't realize that for the REAR AC to work, the FRONT AC button has to be on. I thought that if the rear knob was pointing at the blue AC button, that should activate the rear AC. But I didn't realize the rear AC shares refrigerant with the front AC until I started researching the "problem".

When the front AC is on, the rear blows noticeably colder. I'll do a temperature check with my thermocouple next time I get a chance, but, yeah.

Thanks!

Michael

.....

Thanks to everyone for the advice. This is embarrassing, but I think the A/C is working properly. I didn't realize that for the REAR AC to work, the FRONT AC button has to be on. I thought that if the rear knob was pointing at the blue AC button, that should activate the rear AC. But I didn't realize the rear AC shares refrigerant with the front AC until I started researching the "problem".

When the front AC is on, the rear blows noticeably colder. I'll do a temperature check with my thermocouple next time I get a chance, but, yeah.

Thanks!

Michael

+++++++++++++++++++++++++++++ Yes, for the rear to work, the front has to be on.

As mentioned, a refrigerant's temperature and pressure are directly related. Pure propane (R-290) is always 0 PSIG at -44° F, R-134a is always 0 PSIG at -15° F

R-134a is always 28 PSIG at 32° F, hence you want the low side pressure as close to 28 PSI without going under.

The cheap gauge that the cans have tell you nothing, cars are charged by weight of refrigerant from a vacuum. Attempting to "top off" a partially charged system is always a guessing game.

This is especially true on vehicles like mine which have a variable displacement compressor, these regulate the low side pressure without cycling so it will always be at the set point all the way from having less than an ounce of liquid refrigerant up to being slightly overcharged, making that gauge meaningless.

Barring a weight/mass charge spec then a fixed orifice system is charged by suction superheat, this is what "larrymoencurly" is measuring with the 2 thermometers, but it is more accurate to use the temp scale on a good pressure gauge along with the thermometer on the evap outlet. IE if the gauge says the refrigerant is boiling at 32° F in the evaporator and the thermometer on the suction line reads 42° you have 10° of superheat. Some positive superheat is required to know for sure that no liquid is making it back to the compressor inlet, but too much superheat means that only part of the evaporator is evaporating refrigerant, and you want as much of it in use as possible for the coldest vent temperatures and best dehumidifying. Suction accumulators help to keep liquid from getting to the compressor.

Expansion valve (TXV/TEV) systems are charged by liquid subcooling because the valve controls the suction superheat automatically, this requires a high side gauge with a temp scale and a thermometer on the liquid line. Once again if the gauge says that the refrigerant is condensing at 100° but the liquid line is only 80° you have 20° Positive subcooling is required because vapor bubbles in the liquid to the expansion valve impair its function, but once again too much subcooling means that the liquid is backing up into the condenser and reducing its effective size. Liquid receivers help to keep a solid column of liquid (no vapor) to the expansion valves. This is also the reason for the sight glass, to let you know if there are bubbles in the liquid.

Luckily with cars subcooling and superheat will be correct if you charge an empty functioning stock system by weight to spec.

I am impressed with your knowledge. Is variable displacement fairly common in cars today. I own Toyotas. Is that what they use. I have noticed no cycling. I have noticed also that A/C systems seem to last the life of the cars. The old GM systems from the 70-80's used to crap out or burn up a clutch seemingly all the time.

...

And, yeah, I finally got my thermocouple out and the rear is working quite well.

I measured bet. 80 and 85 degrees with just the blower on, then when the AC started, it dropped to around 60 or so... then as we drove some more, I gave the thermocouple to the kids, who said the lowest temperature they got was 30 degrees (?!!) I still can't believe that, but it sure feels cold so it's good enough for me.

Thanks everyone!

Michael

Some of the GM compressors had well known shaft seal problems. They started leaking early in life. There were, I believe, aftermarket or redesigned, seals that would stop this problem.

I never had any problems with clutches. Compressors beat them to the punch.