A/C recharge from a can.

[jnever1]

Hello,

I recently used a DIY R134a (pure, no additives) on my 95 Q in order to address a long term weak A/C issue. Everything worked fine otherwise (occasionally the fan switch sticks on high only, but it generally remedies itself after a minute or two). While I feel like the end result has been positive (A/C blows quite cold now) the FSM has left me with some concerns.

Namely, the FSM indicates a full charge of refrigerant to be 400g (14.1 oz) (FSM pg HA-104).
Capacity is indicated @ 27.5-29 oz (0.800 +- 0.025 kg) (FSM pg HA-112).
Low Pressure is supposed to be (somewhere between) 28.0 - 33.3 psi between 85-90F @ 50-70% humidity (FSM pg HA-50).

My Q gulped down 12oz from the can.

I'm at roughly 32psi @ 91F amb, 50% humidity.

I'm concerned about overcharge due to the input of 12 oz of refrigerant and the lack of clarity regarding capacity vs. system pressure. Does everything look good?
I don't want to blow anything up!

Thanks

[qship96]

Pressure measurement is a lousy way to determine proper refrigerant levels, just too many variables like outside temp,humidity,compressor condition,condenser cleanliness,airflow,partial line blockage, etc etc...the list of variables that affect what number you read on a gauge is HUGE.

The only way to properly charge system to exact correct level is to evacuate and recharge by weight,period.Everything else is a crapshoot at best,and just a few ounces over/under both affect the performance of the system greatly,which is marginal at best on the 94-96Q compared to other cars.

[ImStricken06]

follow my instructions here:

how-to-recharge-ac-on-2008-rogue-t559692.html

[qship96]

follow my instructions here:

how-to-recharge-ac-on-2008-rogue-t559692.html

POOR advice,all the way,from the product used,to the procedure,to venting to the atmosphere.Exactly what you DONT want to do.Spend the $80-100 to have it done correctly, by a professional, using the eve/recharge machine if you want it done correctly.

[ImStricken06]

follow my instructions here:

how-to-recharge-ac-on-2008-rogue-t559692.html

POOR advice,all the way,from the product used,to the procedure,to venting to the atmosphere.Exactly what you DONT want to do.Spend the $80-100 to have it done correctly, by a professional, using the eve/recharge machine if you want it done correctly.

let me take a stab - you own a shop?

[jnever1]

My thanks for the replies but neither addressed my concern: Based upon data given, have I overfilled my system to a point where I should depressurize appreciably?

While I certainly agree that venting to the atmosphere is not PC now-a-days, I also feel that it is ridiculous to pay someone $80-100 to lift my hood, hook up two lines to my car using quick connects, push some buttons on a digital key pad and then enjoy a smoke or double flag time. I spent $25 on the kit I used and half of that was for the transfer tool.

I know from personal experience that the hardest part of the self-contained evac/recharge station process is looking up how much refrigerant to key in to the machine. This is the part I am having difficulty reconciling with respect to a less-than-clear FSM. Exactly how much refrigerant does my Q require? The manual is sending me mixed messages.

I know enough about phase-change thermodynamics to do my own calculations to enumerate how much R134a I have in my system, given a gauge reading of limited precision. PV=nRT is a good enough estimate for this application in my opinion.

With this in mind, it is worth noting that I haven't had my a/c serviced in over 7 years. This is plenty of time for a few ounces of 1,1,1,2-tetrafluorothane to sneak past a couple of rubber service port o-rings. Since I'm not seriously over the upper threshold of the FSM limits, given atmospheric conditions stated, I'm just going to assume that my Q was probably close to 10 oz low and that the can could not possibly transfer 100% of its contents.

Observations my assumption is based upon:

A/C worked before adding refrigerant (system holds at least some pressure)
A/C worked up to a chill eventually, it simply took a LONG time (mass of available phase-change medium probably low)

A/C improved after refrigerant added (probably added a small amount more than ideal)
LowPressure reading is < 35 psi @ 650RPM on a hot, wet day. (system at upper end of spec)

That said, yes, complete evac (so that the assumption of mass refrigerant = 0 can be reasonably made) followed by fill to spec by weight would have been the best option.

I did not choose that option.

Regardless, since improvement has occurred I will take my Q as improved and consider this issue resolved, if only by happenstance.

[maxnix]

Well, if you were that low, than the level of lubricant is suspect. Too much, the compressor works too hard and fails early. Too little, and the compressor generates too much heat and fails early. Basically why an automotive AC professional is the best recourse not to let refrigerants into the atmosphere and to get the correct amount of the proper oil in the system with nothing else. Good to replace the dryer while you are doing all of this too.

[ericthered]

Way back when I did work on cars.... the lesson was that evacuating the AC system often led the seals loosening and then not resealing.

So when my 94 Q45 A/C was getting unbearable after 15 years without a recharge, I wanted it topped off. I got talked into an evacuate and recharge. Worked perfect for a month, maybe, but after three months it was worse than before the recharge.

So now I went by adding refrigerant by pressure. I had a table to correct for ambient temperature, but that was not too accurate. I went up to 40+ psi or so, but the A/C was still pretty weak. I ended up just north of 50 psi with happier A/C. Not so sure it is holding, though. Haven't gone back and checked pressures, or driven the car much mid-day.

[GSUjinih]

The only way to properly charge system to exact correct level is to evacuate and recharge by weight,period.Everything else is a crapshoot at best,and just a few ounces over/under both affect the performance of the system greatly,which is marginal at best on the 94-96Q compared to other cars.

Marginal at best? Hmm I have been in other much newer Nissans and my Q seems better than them. It was around 96 today and I was very comfortable in my Q!

[hoov100]

The only way to properly charge system to exact correct level is to evacuate and recharge by weight,period.Everything else is a crapshoot at best,and just a few ounces over/under both affect the performance of the system greatly,which is marginal at best on the 94-96Q compared to other cars.

Marginal at best? Hmm I have been in other much newer Nissans and my Q seems better than them. It was around 96 today and I was very comfortable in my Q!

That isn't saying much, it's been 116* and I've been comfortable with nothing but the windows down.

The point is, just adding enough to make the pressures correct on a gauge isn't the same as having the correct amount of refrigerant in the system. It's like saying I have enough oil in my motor to produce the correct amount of oil pressure, but don't know if I have the actual required amount of oil.

[GSUjinih]

Well with less than 10% humidity I imagine you could be comfortable if the car is moving....however I am calling BS if you are comfortable in any traffic at that temperature. Try 50+ humidity and triple digits and that is saying something...

[hoov100]

Well with less than 10% humidity I imagine you could be comfortable if the car is moving....however I am calling BS if you are comfortable in any traffic at that temperature. Try 50+ humidity and triple digits and that is saying something...

Spent basic training in the ozarks wearing full body armor, 70 pound ruck sack at 102* with 90% humidity marching through the woods and mountains. I would GLADLY take your humidity over actual heat and sunshine. There is a reason car manufactures test cars in the southwest and it isn't for the beaches. Humidity sucks, but when it's 120* in a desert with 150* heat coming off the pavement out you are going to know if the cooling system is up to snuff.