R134 pressure numbers, it's low??

[pjtoledo]

2000 Ranger, AC not cold enough. some cooling, but not enough to make wiffie happy.

ambient temp 86

clutch cycle on time 4-5 seconds

low side goes from 36 to 15 when clutch is on
hi side from 125 to 150


after waiting 5 minutes off, pressure slowly settled to 94 low and 105 hi..


tried to add gas from old can, not much pressure left in can, it (can) did cool down a little.


after gas and running 20 minutes low side is now 37-17, hi side is 135-175.

not much change registered by "hand thermometer" in cabin.


my guess is it needs more gas, what hi side press should I look for?


thanks, Perry

 

[Denisefwd93]

Note, If you are checking at Idle everything changes at highway speeds

You're almost there! (best way is to weigh it in)
Hi side is tricky because they don't read true

Also 134A is slow. 20 mins is just about how long it takes to get it "percolating"

Should be (@86 ambient) Hi around 170-180 (although you may never see it that high) Low around 40 +-

http://sporlanonline.com/literature/misc/Form1B.pdf

 

[adsm08]

I didn't have to read past 4-5 seconds to know it is low. Clutch should stay on at least 10-15 seconds at a time.

It is best to weigh it in on an R134 system. Second best is to have a temp/humidity/pressure chart and then charge it that way, but to do that correctly you need to have the chart, know the relative humidity at your location, and monitor the temp at the register as well.

 

[pjtoledo]

update, didn't screw it up too bad

short version:
added gas while timing clutch on time for changes.
as system came to operating temp "added gas" became "too much gas"

that happened real fast, went from clutch on time of 8 seconds to always on as the low wouldn't drop far enough.
at that point the high side was hitting 300 and low only dropped to 30 then rose to 33.

bleed some gas off in small increments until low dropped to cutoff at 17. that brought hi down to about 235.
at idle in neutral the clutch on time was 15-18 seconds.

its better now, not perfect, but good enough for a 2000 with 117,000 miles on it.

 

[adsm08]

And that is why you can't charge 134a by pressure.

Also because the oil doesn't mix into the refrigerant, it pushes the oil around, so if you are low all the oil collects in the accumulator, and then you are basically running the compressor dry.

 

[Denisefwd93]

Do we dare ask how many cans you used?

What was the outdoor temperature?

A better way to check 0peration , is raise and hold the idle 100- 1500 rpm.

 

[4x4junkie]

How I approach this is to feel how cold each fitting is at the evap housing (an infrared thermometer could be used here as well). If the refrigerant is low (but there is still some amount of cooling), you'll likely find the upper fitting a good 20-40° warmer than the lower fitting (this because the low level of refrigerant fully evaporates to a gas before it has a chance to exit the coil).

What I do in this case is fill with refrigerant until the upper fitting drops to within 5-10° of the lower fitting (you'll know right away too, as it'll drop pretty sudden when the boiling refrigerant reaches that level), indicating there is now liquid refrigerant flowing through the line, leaving a small surplus of liquid to collect in the accumulator (it's purpose).
I try to do this on a fairly warm day (90°F or so), as the amount of refrigerant that stays liquid tends to be lower when it's warm.

Depending on ambient temperature, it can be completely normal if the compressor doesn't cycle on/off (usually it'll run constant when it's very hot out and the fan is on max).

 

[Denisefwd93]

My oh my, All these "ways" of charging systems...

Refrigerants are a change of state compound that goes from liquid to gas, gas to liquid, depending on pressure and temperature,

Most people know water boils at 212 degrees sea level. Refrigerants boil the same way, but at much much much lower temperatures.

Refrigeration and air conditioning systems operate on a temperature split or temperature rise,

Compression of refrigerant gives Heat, evaporation (or expansion) of refrigerant absorbs heat

The temperature split / difference in air conditioning is 15 to 20 degrees rise on the condenser side, 15 to 20 degrees lower on the evaporator side. Those temperatures are found on the chart or
gauges and the corresponding pressure can be determined.

Basically, with refrigerant if you know which refrigerant you're using (134a, )
You will know the temperature or pressure by looking up either

Air conditioning temperatures should always be in range of the temperature split.

It's almost impossible to read the temperature on the Automotive condenser because there is a radiator right behind it.

Reading temperature at the evaporator is easier, but the temperature reading should be taken at the coil not at the ductwork in the dashboard.

Most Automotive Systems use a orifice tube which essentially does the same thing as a thermal expansion valve.

It is ALWAYS right to weigh in.
refrigerant. This must be true, if technicians are telling people that is the right way, but people without experience continuously try to read gauges and charge by guage.

To summarize, if you going to use or try to read gauges, at least know or try to understand what you're seeing. The dial / face of a gauge, is basically a circular TP chart ( temperature pressure)

If you see a pressure you can see a (corresponding) temperature.

Hope this helps a little!

 

[pjtoledo]

Do we dare ask how many cans you used?

What was the outdoor temperature?

A better way to check 0peration , is raise and hold the idle 100- 1500 rpm.

less than a full can, about 85 degrees. and I was using leather gloves.
during the add gas phase I kept close watch on the hi side and clutch on time. can had a gauge on it, sure its real accurate
the hi pressure was slow to increase, the on time stayed the same for numerous squirts. I was letting it run to stabilize between squirts. after about 15 minutes of these small squirts the next one took the on time from 6 seconds to about 9 seconds. I figured it was close, one more should do it. that pushed it too far, the clutch stayed on and the hi side hit 300. put the low gauge back on and saw it was only dropping to 30 as the compressor kept running. then it played the same trick, only in reverse. as I bleed off pressure nothing changed for a while, then it started to drop. from there it bleed off consistently and it was easy to slowly approach the 17 psi cutout.


for the bleeding process I left the valve open in the line going to the low side gauge. every time I pulled the hose off it released the gas that was in the hose and gauge. that took some time, but did work and was controllable.


thanks for the input guys, and gal.

 

[Craig0320]

Just wondering. Did you have the fan speed set to high when you charging it?

 

[Denisefwd93]

I guess now would be a bad time to mention that "recovery of refrigerants" is the law, obviously does not apply to 134 or, does it? [emoji3]

 

[4x4junkie]

My oh my, All these "ways" of charging systems...

Refrigerants are a change of state compound that goes from liquid to gas, gas to liquid, depending on pressure and temperature,

Most people know water boils at 212 degrees sea level. Refrigerants boil the same way, but at much much much lower temperatures.

Refrigeration and air conditioning systems operate on a temperature split or temperature rise,

Compression of refrigerant gives Heat, evaporation (or expansion) of refrigerant absorbs heat

The temperature split / difference in air conditioning is 15 to 20 degrees rise on the condenser side, 15 to 20 degrees lower on the evaporator side. Those temperatures are found on the chart or
gauges and the corresponding pressure can be determined.

Basically, with refrigerant if you know which refrigerant you're using (134a, )
You will know the temperature or pressure by looking up either

Air conditioning temperatures should always be in range of the temperature split.

It's almost impossible to read the temperature on the Automotive condenser because there is a radiator right behind it.

Reading temperature at the evaporator is easier, but the temperature reading should be taken at the coil not at the ductwork in the dashboard.

Most Automotive Systems use a orifice tube which essentially does the same thing as a thermal expansion valve.

It is ALWAYS right to weigh in.
refrigerant. This must be true, if technicians are telling people that is the right way, but people without experience continuously try to read gauges and charge by guage.

To summarize, if you going to use or try to read gauges, at least know or try to understand what you're seeing. The dial / face of a gauge, is basically a circular TP chart ( temperature pressure)

If you see a pressure you can see a (corresponding) temperature.

Hope this helps a little!

lol

Or you can just simply fill until the upper line from the evap to the accumulator turns cold.

It's kindof the same thing as filling an expansion-valve system until there's no bubbles in the sight-glass.

In both cases it's not really necessary to know beforehand how much refrigerant is already present in the system... So while I would agree evacuating and then weighing in may be the ultimate best way to charge an A/C system, it is not the only way acceptable.

Lots of helpful info is available over at www.autoacforum.com.

Tip:
Placing the refrigerant can in a pot of hot water will force the refrigerant out of the can and into the system MUCH quicker (takes maybe a few minutes per can).

I guess now would be a bad time to mention that "recovery of refrigerants" is the law, obviously does not apply to 134 or, does it? [emoji3]

Yes it does (law prohibits discharging "R-134a" into the atmosphere).
Though quite oddly enough, sale & discharge into the atmosphere of so-called computer duster & freeze sprays (used to find electronic circuit faults) is completely unregulated AFAIK. Such sprays consist of 1,1,1,2-Tetrafluoroethane, which just so happens to be the exact same compound as R-134a. Go figure.

 

[JerryC]

short version:
added gas while timing clutch on time for changes.
as system came to operating temp "added gas" became "too much gas"

that happened real fast, went from clutch on time of 8 seconds to always on as the low wouldn't drop far enough.
at that point the high side was hitting 300 and low only dropped to 30 then rose to 33.

bleed some gas off in small increments until low dropped to cutoff at 17. that brought hi down to about 235.
at idle in neutral the clutch on time was 15-18 seconds.

its better now, not perfect, but good enough for a 2000 with 117,000 miles on it.

This might be of help.
http://rechargeac.com/how-to/ac-system-pressure-chart

my 2 cents, I'd guess you have more issues, clogged (airflow) condenser/radiator, bad fan, etc.. restricting airflow. I've been told to try hosing the condenser down and if the high side pressure falls dramatically you are looking at an airflow issue.

 

[Denisefwd93]

A wet condenser will always show a lower head pressure, when it's dry, it will go back up again, when fast charging through the low side, the head pressure will jump dramatically, that's why it's always good to add slowly. Usually the warmth from a person's hands is enough to move R12 or R134 into the system just by holding the container, hot water is a good choice also.

it's always good to wash the condenser fins

 

[JerryC]

Yes, just wetting the condenser will lower pressure. I "assumed" by the advice given that the better the condenser is being cooled by the fan the less effect wetting will have.

With idle speed pressures of 30/300 something seems pretty seriously wrong. There is a small chance the gauges are wrong, renting a different set as a check is probably a good idea.

What are the pressures at 2000 rpm? are they climbing steadily higher with rpm? If so at what point does the compressor cut out, wear out or give out?