Experts, please read. How to recharge A/C more...

[rnln]

First I have to say that I did a lot of search and play with recharging many times but I never feel comfortable because I never understand for sure/clear. Below I will have some questions and also picture of my gauge.

How:
1- hook up the middle line to 134 tank.
2- pop the 2 connectoers to the car.
3- start the car and jam the pedal to have it run at 2k rpm
4- open blue knob to charge low side. I see fluid run through the clear glass window for probably several seconds then close the blue knob
5- open the red knob to release the high side. I also see fluid run through the clear class, for several seconds. Then close red knob.
Repeat (4) and (5) untill the gauges reach the points.

What is the points:
After a lot of reading and searching, I found that I should be running around 18-20 on low side and between 250-300 on the high side.

Problem:
1- I don't know how to read my gauge. At some points, I thought I did but then think about it again, I think I don't. There are total 3 different layers of number on the gauge, most inner, middle, and most outer layers of number. Which one I should be reading at?
2- The picture below is my gauges set without anything connected to them and knobs are opened. Is it correct? Why are the gauge have some reading? Isn't it suppose to be all zero when not connected, and knobs are opened?
If my gauges are ok, what are they reading now? The narrower tips, ot the end with the fat arrow?

In the past, more than once, I did made my A/C very cold but everytime doing it, I got very scared. Today, while while charging it for the first couple second, my compressor make lound noise plus the normal scary feeling, I took everything off and make a big coffee cup

[DRACO A5OG]

Here you go RnLN http://autorefrigerants.com/Envirotechnical.htm

[mthomas58]

STOP. If you don't have an A/C servicing book, I would recommend you pick one up a read through the charging procedures and safety warnings. The high-side RED valve should NEVER be opened during charging.

From the Snap On Manual:

"CAUTION. DO NOT open the high side hand valve while the air conditioning system is in operation. If the high side hand valve is opened while the system is operating, high pressure refrigerant will be forced through the high side gauge and to the refrigerant can if it is attached. This high pressure could rupture the can or posssibly burst the fitting at the safety can value resulting in damage and physical injury"

Link to Snap On A/C Traning Manual: http://buy1.snapon.com/catalog/searchLN.asp?partno=ACT279&searchTrnsfr=true&search_type=Part&store=snapon-store

[Tigerrat]

You can get manuals/info from this site and their forum. http://www.ackits.com/

Yep. You should be charging a working system from the low side only, gas not liquid. Dangerous to do otherwise. Suggest a little more research/planning. Ken

[bazar01]

Originally Posted by rnln

First I have to say that I did a lot of search and play with recharging many times but I never feel comfortable because I never understand for sure/clear. Below I will have some questions and also picture of my gauge.

How:
1- hook up the middle line to 134 tank.
2- pop the 2 connectoers to the car.
Purge the trapped air from the low(blue) and high (red) side and yellow charging hoses by slowly opening the fitting on the manifold end until refrigerant comes out. Then close.
3- start the car and jam the pedal to have it run at 2k rpm
4- open blue knob to charge low side. I see fluid run through the clear glass window for probably several seconds then close the blue knob
5- open the red knob to release the high side. I also see fluid run through the clear class, for several seconds. Then close red knob.
Repeat (4) and (5) untill the gauges reach the points.
The points mentioned are the correct operating pressures.
What is the points:
After a lot of reading and searching, I found that I should be running around 18-20 on low side and between 250-300 on the high side.

Problem:
1- I don't know how to read my gauge. At some points, I thought I did but then think about it again, I think I don't. There are total 3 different layers of number on the gauge, most inner, middle, and most outer layers of number. Which one I should be reading at?
The pressure scale is the outermost scale in black.
2- The picture below is my gauges set without anything connected to them and knobs are opened. Is it correct? Why are the gauge have some reading? Isn't it suppose to be all zero when not connected, and knobs are opened?
If my gauges are ok, what are they reading now? The narrower tips, ot the end with the fat arrow?
There must be some residual refrigerant from a previous hook up. Just open the hose fitting on the manifold end to zero the gauges before hooking up to your system. If you know it's the same refrigerant, just hook it up to the system.

In the past, more than once, I did made my A/C very cold but everytime doing it, I got very scared. Today, while while charging it for the first couple second, my compressor make lound noise plus the normal scary feeling, I took everything off and make a big coffee cup

Charge only on the low side when topping off with the refrigerant cylinder upright.
Work safe. Safety glasses.

[JFairman]

if you opened the red high pressure line manifold valve while the compressor is running you've probably teaked the low side gauge out of calibration by hitting the low side 120psi gauge with over 200psi and it's not reading accurately now anyway.
does the low side gauge needle return to zero after disconnecting the hoses?

there are alot lof things to know about different types of AC refrigerant charging, and some specific to air cooled 911's.

after evacuating for around 3 hours or longer on a hot day you can hook up the yellow line to the refrigerant bottle and unscrew the brass hose fitting at the manifold gauge slowly to let all the air in the hose purge out. then tighten it.
at this point there is no air in the hoses, manifold gauges and your AC system so you can start charging.

the initial charge with a fully evacuated system and engine OFF can be charged slowly with liqued refrigerant (bottle upside down) through the high side fitting on the compressor until the pressure has equalized and no more refrigerant flows in.

open the high side valve SLOWLY so liqued flows in gradually. it's still alot faster than charging with gas from the start.
and, in a way it can be better than initially charging through the low side fitting because incoming refrigerant won't be forcing the oil in the compressor out into the low pressure suction hose.
then once pressure has equalized close the valves on the manifold gauge.

now turn the refrigerant bottle right side up so only gas will come out.

start the car with the rear lid down so air is being drawn in over the condensor.
turn on the AC and slowly open the low side valve so gas will start to be sucked in.
Do Not open the high side valve while charging with the engine running, and do not charge with liqued into the low side with engine running because the compressor can't compress liqued and the seals will be damaged.
and don't charge into the low side with liqued with the engine off either because that will force the oil in the compressor out of it and into the high side line. there are check valves in the compressor...

to get the pressures right you'll have to study the ambient temperature/pressure tables and do a little math.
http://www.ackits.com/aacf/ptchart.cfm


R12 is much more forgiving, while the pressures with R134 run a little higher and have to be very close to right on to blow cold air.

**************************************************
This is written by someone else and it may help you too...

"To find a better P&T working relationship with R134a there is a rather good "rule of thumb" stated by the manufacturers of R134a and the auto industry in general and that is "with R134a pressures tend to be 10% greater". However this rule of thumb is specific to an ambient temperature range. What I mean by specific range is that starting near 80F ambient R134a tends to run at a higher pressure than R12, and that difference is is more like an upward curve moving away from the R12 diagonal line. Once you start moving toward 95F ambients the curve shoots upward and the higher you go the straighter it climbs. So "we" have new factors or multipliers which we can safely apply to R134a or given "normal ranges of operation", say anywhere from 85F to 110F (desert people don't use refrigeration systems anyway, they use swap coolers). So this is how you estimate to a better finite target with R134a:
you recall the relationship with R12 was "2.4" (2.4 times the ambient should be the mean target for the high side pressure). The ranges for R134a "we" work with look something like this:

80-85F = ambient times 2.4 X 1.05 or the + 5% rule
86-90F = (ambient times 2.4) X 1.1 or the +10% rule
91-95F = ambient times 2.4 X 1.13 or the +13% rule
96-100F = ambient times 2.4 X 1.15 or the +15% rule
101-105 = ambient times 2.4 X 1.17 or the +17% rule
106-110 = ambient times 2.4 X 1.20 or the + 20% rule

Here is how you apply the rules:
Say you have charged the system with a known quantity of R134a refrigerant (grams or ounces or whatever) and the ambient temperature is 95F. Take 95 and multiply it by 2.4 = 228 psi and then multiply that by 1.13 = 258 psi. Now consider if you really had this pressure well that would be in a perfect world. Depending upon whether you parked on black asphalt or if the expansion valve was opening or closing this mean target of 258 might swing up to 270 or so and frankly that is pretty good in a 911 with R134a at 95F. Or, if you are testing with the deck lid down and your services hoses are holding the deck lid up an inch or two that would reduce the effective air flow across the deck lid condenser and drive pressures upward. Other things that can drive up the high side might be the sun beating down on the deck lid or maybe you just completed a few 0-120 mph test runs up and down your driveway (like I do).

And then you ponder your low side psi. Is it within a typical norm of 20-40 psi? : however knowing low sides usually move upward with the high side. The low side pressure does not mean a thing unless you have some vent temperature readings, and vent temperature readings, although low ones are your goal, don't really tell the true story unless you thermostat probe in the evaporator core and check the core temperatures."

[LynnsABCs]

I didn't see it mentioned, go to Harbor Freight and buy the vacumn pump that hooks up to your air compressor. About $15.

Hook up low side hose to low side, high side hose to high side and center hose to the vacumn pump. Run a vacumn for a couple of hours (helps remove moisture). Car is not running while doing this.

Let it sit overnight and see if you loose pressure. Avoids leaks after you recharge. Might want to consider changing the receiver/dryer for long-lasting cooling results.

If charging with small cans, put in a pan of warm water and it will fill quicker. Don't turn can upside down and risk straining the condensor.

Consider going to thesamba.com and reading the long thread about working on A/C systems. Also, for safety, add a pair of work gloves with safety goggles.

[JFairman]

those low cost air compressor > venturi type vacuum pumps are sort of ok to almost adequate for small domestic car AC systems that have all the components packed into a small area around the engine, dashboard, and firewall while using around 8 feet of hoses... but they won't ever do a good job of evacuating the air and boiling out all the moisture in a 911 which has over 40 feet of hose and heat exchangers and hardware mounted in each end of the car and in the middle.

on top of that running the average shop air compressor nonstop for 2-3 hours with one of those venturi vacuum pumps will overheat and kill it, or wear it out quickly.

to do a good deep evacuation you need a good 2 stage dedicated electric motor vacuum pump with fresh oil in it.
good ones are around $250 on up, and it's best to do the evacuation on the hottest day possible.

[LynnsABCs]

The vacumn pump seems to work OK for guys with Vanagon A/C systems (now that's some long hoses). Don't think I'm going to worry about wearing out a $15 pump for my personal use on 2 cars maybe using it every 2 yrs or so. I would agree it wouldn't work/last in a production shop.

Also, running my Sear air compressor for 2 hours every year or so is not going to be a problem. I think this alternative is superior to having a commercial shop do their normal 30 minute evac before charging. Would be nice to find out if you have a leaking hose, o-ring or fitting.

[JFairman]

"Don't think I'm going to worry about wearing out a $15 pump"
i wasn't talking about the venturi vacuum pump. it's not even a pump, but i don't know what else to call it.
when i worked in a shop 20 years ago and we did 10 minute quickie evacuations and charged with R12, thats what we had to use. there's not one moving part in it so it will never wear out.

running an air compressor on one of those is the same as hooking up an open hose to a compressor and letting it run continuosly... that will overheat the compressor during a 3 hour evacuation on a 911 and cause alot of wear on the air compressor.
and those venturi vacuum pumps for auto AC will not suck down as low a vacuum as a good motorized 2 stage vacuum pump.

[CBRacerX]

About to evac and charge my updated system, this is very helpful!

[rnln]

Thanks guys,

Bajar01,
So if I open it up and it's still not zero out, should get air compressor to blow into the gauge's ports?

JFairman,
The picture above shows the gauge alone, disconnected and away from tank and car. Both blue/red knobs are opened. Is my gauges bad now? oh no... I have been putting thet ank up side down, opening low and high side valve (red/blue knobs) alternatively. So my compressor can be bad too?

Let see if I get the idea correct. Since my system is already there, I can ignore the high side and:
1- hook up everything together as above
2- start the car
3- open low side (blue) to charge the low side.
4- ignore high side. PSI on both sides, low and high, will increase even those only charging the low side?

Thank you.

[rnln]

I hope you expert on gauges set don't mind I switch my questions a little off direction.
Look like my gauges set is bad, above pic. I only used it several times. Called MAC Tools, cost for 2 gauges are $60 + tax or fee etc. If I get HF set brand new is only $50.
I don't care miscellaneous features. All I care is to recharge my 911 once, or twice max, a year. Is it worth to get the brand name? Or can I get other cheaper brand gauges and stick them into my MAC Tools manifold?

[JFairman]

The gauges on your Mac tools manifold are Mastercool gauges. Thats what the MC on them stands for.
I have the same MC gauges, just they are on a MC brass manifold instead.

If you tweaked the low side gauge so it doesn't return to zero try insering a small flat balde screwdriver into the hole in the lense face and turn the zero adjustment screw that is on the bezel.
I think you may be able to rezero the needle if thats the problem.

Ususally there is a little plastic plug in the screwdriver access hole in the lense to keep dust or whatever from getting in there but it is missing on your low side gauge.

[rnln]

I tried that on both gauges but the adjust ment is so much of a little, can't go back to 0. I set it at 70 and that is "my 0" to work on. On the high side, I have 100 as "my 0". Now I am having a different problem when charging and I don't know if it the gauge set problem, or the car's problem.

After vaccumned everything for an hour or so. We started to charge, low side only. At first several seconds, the low side increased around 30-40 PSI, then it jump quick to the high side in a blink of an eye. High pressure gauge increased and low pressure gauge decreased.

We then stopped charging and starting to run the AC to monitor how it acts. In couple minutes reving rpm at 2k, low side is showing 10 psi while high side keep increasing slowly up to 300+ PSI. Remember we were not charging, just running car and turning AC.

Then we released some pressure from the high side and start the car, turned on AC again. Now he high side is lowering down to around 200 PSI, low side was still showing 10 PSI.

Then we charged it a little more from the low side. The strange thing is that whatever I put in there, it go directly to the high side; which means the low side always ended up at 10 PSI and high side increased up to 300+ PSI.

Here is how it acted in detail:
I opened low valve for a second or two. While low valve was opened, low side increased to around 35 PSI. High side stayed.
After low side valve closed, low side back to 10 PSI, and high side increased. I stopped and called it the day when high side increased up to 300+ PSI.

Driving the car in the evening, I get around low 50 degrees. The max I ever got on this car before was below 35 degrees.

Question, does low side suppose to go and stay up at around 20-30 PSI? The first thing we could explain this is bad gauges set???

[JFairman]

Hard to say whats going on with your gauges without actually seeing what you are doing.
The high side gauge reads high pressure if the hose is connected to the high side shrader fitting even when the knob is closed, it's just not connected internally to the yellow charge line and the low side if the low side knob is open at the same time.. It's hard to explain.

With the 300psi high side reading it makes me ask, are you closing the rear lid as far as you can so air is being drawn in over the rear condensor by the engine fan to cool it? If you don't have air going over the condensors the high side pressure will go way too high.. possibly blowing a seal or hose.

I always charge with liqued into the high side slowly with the engine off till no more goes in.
Then close the valves on the gauges and start the car and turn the AC on and charge at idle speed into the low side only while giving the bottle of refrigerant a quick tip to the side every now and then to throw a splash of liqued in with the gas to speed up the gas charging.. but i guess there's more than one way to do it.

[rnln]

Regarding the below. This is exactly what I did. Close the high valve on the gaguse manifold (always closed), open the low gauge manifold valve to give the low side some PSI, but whenever this knob is closed/done, low side turn back to 10 psi and high side increased. Look like whatever I put into the system, it flows right into the high side after I am done.

"Then close the valves on the gauges and start the car and turn the AC on and charge at idle speed into the low side only while giving the bottle of refrigerant a quick tip to the side every now and then to throw a splash of liqued in with the gas to speed up the gas charging.. but i guess there's more than one way to do it."

[BMWDr]

Seems to me this has become a lot more confusing than it needs to be! The freon is not "flowing" from a low side static location to a separate high side static location. Your freon flows continually. Your low side pressure goes up when you open your low side due to pressure from your freon tank. A few seconds is not going to add a lot of freon. The reason you see the high side start moving quickly is because the pressure is moving further past it's boiling point. As JFairman said it's important your engine cover is closed to keep air moving over the condenser. You can use a water hose to do the same thing by misting it over the condenser and simulating a more moving vehicle situation. With your engine running about 1500 rpm, water keeping the condenser cool, you should have 25 to 35 psi low. The key is that your high side needs to stop at around 250 psi with water over the condenser. Adjust it with the low side watching the high side pressure. Now, if your high side is about 250 psi and your low side is 10psi or below you need to replace your expansion valve. That is the pressure control that enables the gas to liquefy and keep us cool. 911's usually have a slightly lower low side due to the distance the freon travels. It's hard to pin down the high side due to condenser being located above an air-cooled motor, in back of the car, and a mile from the evaporator! Porsche never really intended to have AC on their rear engine race cars and asking it work at all was quite a lot to ask of any ac system. But, as is life, young race car drivers become old race car drivers and we demand a certain amount of comforts in our twilight years! Water is the key rnln, that and accurate gauges. Good luck!

[rnln]

ok, today I had access to an almost new, and accurate, set of gauge and try it right away since this thing is killing me with unknown cause.
Hooking up the new set of gauges, open up the manifold low valve, close the engine lid, turn on condensor fan ( I have a big/strong fan on my rear condensor), start the car, jam the pedal to have it's running between 1800-2k rpm. The below were what I was getting:

Outside ambien: 75 degree base on my probe thermostat.

Engine running within 3 mins:
Low side was around 16 PSI
High side was around 230 PSI

After 5 mins running, both sides increased slightly, low side to 18-19 PSI and highside to about 260-270 PSI.

At this point, my thermostat at the vent showed a little lower than 60 degrees. I stopped and cleaned up. What do you guys think?
Everything is stock except the after market rear condensor, not too much bigger than the stock rear condensor. I added a big/strong fan for this rear condensor but I don't think it helps while moving. At red light and slow city moving, maybe it helps a tiny bit. This is 134a.
------------------------------------------------
On the past several days, I have been taking the car out in the afternoon (around 5:30 to 6 pm) and test temp. Let's look at one of the days:
Inside car's cabin: 110 degree.
Outside ambien, thermostat on the grass, in the shade, next to the bush: 80 degree.
Drove around for 3 mins before got on freeway and turned on AC max.
After 3 mins, vent temp got down to 60 degrees.
15 mins later, 50 degrees.
1/2+ hour of driving, outside temp is around 70, vent temp was around 45 degrees.
So look like I am getting around 25-30 degrees below outside ambien temp.
-------------------------------------------------

[ruf-porsche]

Originally Posted by rnln

ok, today I had access to an almost new, and accurate, set of gauge and try it right away since this thing is killing me with unknown cause.
Hooking up the new set of gauges, open up the manifold low valve, close the engine lid, turn on condensor fan ( I have a big/strong fan on my rear condensor), start the car, jam the pedal to have it's running between 1800-2k rpm. The below were what I was getting:

Outside ambien: 75 degree base on my probe thermostat.

Engine running within 3 mins:
Low side was around 16 PSI
High side was around 230 PSI

After 5 mins running, both sides increased slightly, low side to 18-19 PSI and highside to about 260-270 PSI.

At this point, my thermostat at the vent showed a little lower than 60 degrees. I stopped and cleaned up. What do you guys think?
Everything is stock except the after market rear condensor, not too much bigger than the stock rear condensor. I added a big/strong fan for this rear condensor but I don't think it helps while moving. At red light and slow city moving, maybe it helps a tiny bit. This is 134a.
------------------------------------------------
On the past several days, I have been taking the car out in the afternoon (around 5:30 to 6 pm) and test temp. Let's look at one of the days:
Inside car's cabin: 110 degree.
Outside ambien, thermostat on the grass, in the shade, next to the bush: 80 degree.
Drove around for 3 mins before got on freeway and turned on AC max.
After 3 mins, vent temp got down to 60 degrees.
15 mins later, 50 degrees.
1/2+ hour of driving, outside temp is around 70, vent temp was around 45 degrees.
So look like I am getting around 25-30 degrees below outside ambien temp.
-------------------------------------------------

If you want the "LOWEST" vent temperatrure, set your blower fan to the lowest setting.