Liquid 134a in AC

A year or two ago, my 2003 Montana AC was not cooling well, so I added some freon (actually 134a) and it seemed to help. This year's hot spell was mo re than it could handle, and I figured it was an old vehicle and could be l osing freon. I tipped the can upside down, and only later read that that w as a bad idea. Got a cheap gauge and also saw that it was overcharged -- 6

0 or so -- for a few days, and bled it back down to 40 psi. Ambient temp a t these times was around 95-100. Still pretty hot out, and the AC cuts off intermittently.

I'm curious as to why excess liquid wouldn't just eventually go to vapor as well. And what am I missing by not having a gauge for the high pressure s ide? BTW, I've cleaned the coils, radiator, fan, etc.

Questions:

1) Did I actually solve the overcharge condition by bleeding the system (lo w pressure) side down to 40? Or does the liquid freon, as I've been told, actually accumulate somewhere and need to be removed some other way?

2) Since the AC works and doesn't seem to have been actually leaking, what else might be causing the poor performance and intermittent cycling? Or is a combination of the high ambient temp and too much liquid causing the ove rpressure sensor to just cut off the compressor until I can remove the exce ss liquid?

Reply to
gmark
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me freon (actually 134a) and it seemed to help.  This year's hot spell wa s more than it could handle, and I figured it was an old vehicle and could be losing freon.  I tipped the can upside down, and only later read that that was a bad idea.  Got a cheap gauge and also saw that it was overchar ged -- 60 or so -- for a few days, and bled it back down to 40 psi.  Ambi ent temp at these times was around 95-100.  Still pretty hot out, and the AC cuts off intermittently.

as well.  And what am I missing by not having a gauge for the high pressu re side?  BTW, I've cleaned the coils, radiator, fan, etc.

low pressure) side down to 40?  Or does the liquid freon, as I've been to ld, actually accumulate somewhere and need to be removed some other way?

t else might be causing the poor performance and intermittent cycling?  O r is a combination of the high ambient temp and too much liquid causing the overpressure sensor to just cut off the compressor until I can remove the excess liquid?

tipping the can doesn't hurt anything. In fact I've cans that say keep can upright for gas freon, and turn over for liquid gas.

Over filling or under filling the system can cause it to keep cycling.. Maybe you have a bad clutch cycling switch? If it's only cutting out once in a while that is normal to keep it from freezing up. If it's constantly cycling then you have an issue.

The hotter it is outside the slower the freon will enter the system.

Reply to
m6onz5a

ed some freon (actually 134a) and it seemed to help.  This year's hot spell was more than it could handle, and I figured it was an old vehicle a nd could be losing freon.  I tipped the can upside down, and only later r ead that that was a bad idea.  Got a cheap gauge and also saw that it was overcharged -- 60 or so -- for a few days, and bled it back down to 40 psi .  Ambient temp at these times was around 95-100.  Still pretty hot out , and the AC cuts off intermittently.

go to vapor as well.  And what am I missing by not having a gauge for th e high pressure side?  BTW, I've cleaned the coils, radiator, fan, et c.

tem (low pressure) side down to 40?  Or does the liquid freon, as I'v e been told, actually accumulate somewhere and need to be removed some othe r way?

king, what else might be causing the poor performance and intermittent cycl ing?  Or is a combination of the high ambient temp and too much liquid ca using the overpressure sensor to just cut off the compressor until I can re move the excess liquid?

So that stuff about liquid freon saturating the dehydrator or something or other is bunk?

It was only 75 or so last night, and the AC was still sort of wimpy. Is th ere anything that having a gauge for the high-pressure side might tell me?

Also, I seem to recall one can of freon having guidelines for determining h ow much pressure should be in the low-pressure side based on ambient temper ature, which sounds reasonable to me. But other docs say low pressure shou ld never exceed 45 PSI. Of course, that's meant for the casual user, so is it just a really, really rough approximation? Maybe I should add a bit mo re freon, since it's currently around 40 psi when the engine is cold and ju st starting to warm up.

I'm open to all observations!

GMS

Reply to
gmark

gmark wrote in news: snipped-for-privacy@googlegroups.com:

You need to sit down with some one that can explain the AC system more thoughouly to you. you are not understanding what is going on. KB

Reply to
Kevin Bottorff

Try it and find out. I'll give you a hint, Liquids don't compress and the low side port you charge through is in the compressor intake line. Let the compressor get a slug of R-134A in it and you will be replacing the compressor, condenser core, and flushing the system to remove the leftover pieces that made it farther.

The can is labeled because some NON automotive systems and units used to recover and recharge systems can be filled with liquid so they can pump it into the system.

Nothing except what is actually happening, a blockage past the compressor could cause a nice low side pressure and be spiking very high on the high side without the gauge you don't even know if the compressor is actually working.

Engine temperature make NO difference to the AC system, Ambient air temperatures do. NO the numbers are not meant for the "casual user" they are given because overcharged systems like to blow apart from the high pressures.

And until you have a clue you might want to stop playing, unless you really want to replace broken parts.

Reply to
Steve W.

For DIY'ers using 11 ounce - or whatever - cans. Keeping this real simple, for the GM A/C's I've worked on I've found the most useful tool is a simple accurate digital cooking thermometer. The kind with a wired probe to stick in a vent is the easiest to use. Though I haven't used one, a postal scale would be the second tool I'd have. That's for filling a empty system, but can content weights have always been close enough. The specs tell how many ounces the system need.

An empty system (evacuated of course) with good working parts just needs the correct weight added. A couple ounces at a time when you get near the spec weight.until the vent temp stops dropping. When you get close to spec weight, close the can valve. Look at the stabilized temp. Open the can valve for a few seconds. If you've got a 34 ounce spec, and you're on the new 4th 11 ounce can the freon will come out fast. Use you judgement. Don't rush. The thermometer won't run away, and it won't lie. Simple as that. No gages, no heavy thinking. It'll always blow coolest right near the spec weight. Stop.

For the OP, who has what he thinks is poor cooling, and doesn't know how much freon is in there. The thermometer tells you if the system is cooling right. Nothing else. Not your fingers or your face. Find the temp drop from ambient for your vehicle, and measure it. If it's bad, do this. Buy a can or 2 of UV dyed freon. No oil in it, and no stop-leak in it. Hook up a gage set. You want to know the high/low side specs. If either goes 50 psi past the max spec, stop. It's dangerous. Never happened to me, so I can't say what causes that. Ask somebody else, or take it to a shop, IME, loss of A/C cooling has always been a leak or a worn out compressor. Nothing else. I always use gages for the safety aspect. Both low and high side pressure might tell you something, but never helped me much. When I replaced a non-leaking bad compressor I didn't have gages, and I can't remember what the pressures mean. My leakers were always showing pressures within the specs. You can look up pressure specs. So to continue with what I know, start adding freon. If the compressor was already cycling normally, a single can or less might do. Look at the gages. That way you feel you know what the f*ck you're doing, and won't blow yourself up. Check the thermometer. If the temp doesn't start dropping after just a few ounces, I can't help you. A new compressor always worked for me, but some systems can have other issues. I won't speculate on that. If the temp drops to what it should be, stop. You have a leak. Probably slow, but you should be able to find it after a few hours of running the A/C, with a strong UV light and snooping around. Start looking at the easy to get to places first, compressor shaft seal, lines, then the condenser. Evap would be last if I couldn't find it elsewhere. Never had an evap leak, so no excuse to buy a sniffer. I wouldn't stop with the first leak I found, but would still go over everything except the evap. I had a shaft seal AND a very small hard-to-find condenser leak once. Had to do evac/recharge twice because I didn't find the condenser leak first go. Anyway, I hope you got my main point. Good digital thermometer. Measure the ingredients. Act like a good cook.

Reply to
Vic Smith

Thanks tremendously for all this information, Vic!!

Couple more questions. First "OP" - "ordinary person"? Or?

I've read that low pressure specs are 30-50psi and high are 150-200psi. So und right?

I've read that the temperature drop from ambient at the vent should be abou t 20-30 degrees. Sound right?

If there is a leak, it's plenty slow, since the refrig. I added was the fir st time in 200K miles. And I don't see any of the UV dye at all, unless it 's inside the air distributor at the evap.. But still, doesn't seem to be a significant concern at this point.

I guess the cutoff switch is on the high pressure line (?) near the firewal l, and I can put a meter on it to see when it's activating. I'd rather not deal with approximate readings, but the above is all I've been able to fin d on the web. So what would be a reasonable pressure for the switch to act ivate at?

Lastly, you may have guessed I'd like to learn as much about this as possib le, not just to solve the immediate problem, so... sources of documentatio n would be greatly appreciated.

And something I've wondered about -- years ago, I cobbled together an AC sy stem on my 68 chevy using after-market parts, custom brackets, copper pipe, miscellaneous hardware junk, and it was pretty obvious when the clutch wou ld engage, since the compressor was either on or off, period. I was under the impression that factory units were more or less different in that the c ompressor clutch was always on, and the internal pressure was controlled in some other way. I guessed there was some sort of high-to-low pressure byp ass mechanism regulating cooling efficiency. I also guessed that there was some sort of recovery system that would hold excess freon (all R12s at the time), some sort of dessicant somewhere. And that in an idle system, liqu id refrigerant and gas would eventually equalize, with the proportion of li quid to gas governed by the total amount in the system and the equalized pr essure at the particular temperature. I guess overfilling it beyond some c ritical limit would cause the non-compressible stuff to bunch up at the com pressor and wreak havoc.

Oh, and one more thing -- I was discussing this with a neighbor who service s home units and doesn't do cars at all, and he said that all he knew was t hat they were very different -- different tolerances, ranges, hardware, ref rig., etc.. True?

So was I right about any of that? And what am I missing?

Thanks in advance for any info., folks!

GMS

Reply to
gmark

"Original Poster."

Don't know. Depends on the system. I have shop manuals for mine. Get them used on eBay for anywhere from 10-50 bucks. But my son has access to Alldata, so that's another option. A friendly mech can look it up for you. Call around. Think I ended with 45 low 180 high last time I charged my '97 Lumina. Not sure. It was within spec range, but I used the digital thermometer to get there, not the gages.

20-30 degrees. Sound right?

Supposedly, Abe Lincoln was asked "How long should a man's legs be?" His answer was "Long enough to reach the ground." Different systems will vary. What matters is it does the job. And that when the lowest temp is attained, that's the right amount of freon. That was entire point about using the thermometer. As I recall my Lumina drops temp about 30, which always works for us. My GM vehicles all have had a "Max" setting, which recircs the inside air, and speeds the fan. I use it sometimes in Florida when getting into a sun-heated car. R-12 had a bigger temp drop. My wife was always complaining about cold arms in my '88 Celebrity. Turned all the vents toward me.

time in 200K miles. And I don't see any of the UV dye at all, unless it's inside the air distributor at the evap.. But still, doesn't seem to be a significant concern at this point.

A new leak cares squat about the 200k miles before its birth. You never mentioned dye in the system. Or your actual temps. Quit playing around, and post some facts that concern you. I can't say more than I have already without new facts. Then I'll just be guessing unless the facts match my experience. I'm not an A/C guru, and won't play one. All my A/C fixes have been topping up from slow leaks, and replacing bad compressors and condensers. Never flushed a system. In R-12 days I didn't even evacuate. Now I have a good evac pump, but before or since, I've never had a problem charging a system. 100% success rate, not counting when a charge reveals a worn out compressor. Never had an issue with pressure switches. I don't have your car, and don't know what I don't know.

and I can put a meter on it to see when it's activating. I'd rather not deal with approximate readings, but the above is all I've been able to find on the web. So what would be a reasonable pressure for the switch to activate at?

not just to solve the immediate problem, so... sources of documentation would be greatly appreciated.

There's plenty of good general stuff to be found on the net. All the real "documentation" for your vehicle is in the shop manual for your vehicle, or Alldata.

on my 68 chevy using after-market parts, custom brackets, copper pipe, miscellaneous hardware junk, and it was pretty obvious when the clutch would engage, since the compressor was either on or off, period. I was under the impression that factory units were more or less different in that the compressor clutch was always on, and the internal pressure was controlled in some other way. I guessed there was some sort of high-to-low pressure bypass mechanism regulating cooling efficiency. I also guessed that there was some sort of recovery system that would hold excess freon (all R12s at the time), some sort of dessicant somewhere. And that in an idle system, liquid refrigerant and gas would eventually equalize, with the proportion of liquid to gas governed by the total amount in the system and the equalized pressure at the particular temperature. I guess overfilling it beyond some critical limit would

Don't know anything beyond my '97 Lumina and '93 Grand Am. On them I can hear and see the compressor cycle. Can't even remember if they have V5 or HD6 compressors.

home units and doesn't do cars at all, and he said that all he knew was that they were very different -- different tolerances, ranges, hardware, refrig., etc.. True?

You're only missing what you need, but don't have. What's that?

>
Reply to
Vic Smith

It appears that the low side charging port is a sufficient distance from (they're sometimes on top of) the compressor making it likely that any liquid fed from a single consumer sized R134a can, with both small diameter restrictive hose and tapper, almost assuredly flashed before having done the slightest amount of harm.

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In addition to already stated responses, I'd also consider inspecting the orifice tube and clean or replace if necesssary.
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Reply to
Heron

Generally that's right. In most systems I've seen the low side runs down to anywhere from 24 to 32 psi and then cycles off until the pressure rises back to 40 to 44 psi and then cycles back on. The high side pressure will vary with the outside air temperature, generally, the hotter it is outside the higher the high side pressure will be. Some systems, perhaps all new ones, have a high side pressure limit switch that turns off the compressor if the high side gets above

300ish. The highest I've ever seen is around 300 on a very hot day (temps over 100) working on the AC in my garage. Spraying the condenser with water will quickly bring the high side pressure down.
20-30 degrees. Sound right?

Depends on whether you are talking about the drop when idling at a stop or while cruising on a highway. For HOME systems they say look for a 20 degree drop. But on a car system that's cruising on the highway you get a much higher drop, could be 105 outside air dropped to 50 or 60 degree inside air. Recall that the temperature of the evap core is usually very close to the pressure on the low side. So if it's running about 35 psi it will be about 35 degrees. It won't call the air to 35 because the air goes thru it too fast but it should cool it to at least down to 60 or it's not going to feel very cool. If you run it on MAX/Re circulate then it can cool better because it starts with much cooler intake air, usually a mix of inside air and outside air, perhaps averaging around 75 degrees.

time in 200K miles. And I don't see any of the UV dye at all, unless it's inside the air distributor at the evap.. But still, doesn't seem to be a significant concern at this point.

and I can put a meter on it to see when it's activating. I'd rather not deal with approximate readings, but the above is all I've been able to find on the web. So what would be a reasonable pressure for the switch to activate at?

not just to solve the immediate problem, so... sources of documentation would be greatly appreciated.

on my 68 chevy using after-market parts, custom brackets, copper pipe, miscellaneous hardware junk, and it was pretty obvious when the clutch would engage, since the compressor was either on or off, period. I was under the impression that factory units were more or less different in that the compressor clutch was always on, and the internal pressure was controlled in some other way. I guessed there was some sort of high-to-low pressure bypass mechanism regulating cooling efficiency. I also guessed that there was some sort of recovery system that would hold excess freon (all R12s at the time), some sort of dessicant somewhere. And that in an idle system, liquid refrigerant and gas would eventually equalize, with the proportion of liquid to gas governed by the total amount in the system and the equalized pressure at the particular temperature. I guess overfilling it beyond some critical limit would

There have been a lot of different methods for regulating the freon/cooling flow over the years. There have been systems that kept the compressor on all the time and used other means of keeping the freon flow controlled so that the evaporator maintained a steady 34 degrees. I know GM did it like that for years and it's why IMHO GM systems generally out cooled everyone else's. GM also developed a variable displacement compressor, I know my 93 Corsica had one and I think my 2000 Malibu used one. The compressor somehow senses what the system pressures are and adjusts it's piston stroke to maintain the desired pressures rather then turning the compressor on and off all the time like my ford systems do. The most common system seems to be the Controlled Cycling Clutch and Orifice tube system like Ford and many others use. It just has a switch measure low side pressure and cycle the compressor on and off the keep the pressure between 38 and

42 psi. Not as elegant as teh variable displacement compressor GM uses. There are also systems that used the same cycling clutch system based on pressure but that use an expansion valve instead of an orifice tube. Why one over the other? I don't know.

home units and doesn't do cars at all, and he said that all he knew was that they were very different -- different tolerances, ranges, hardware, refrig., etc.. True?

Reply to
Ashton Crusher

I use my trusty radio shack thermometer on long wire. Insert into vent, fan low.

I usually get over a hundred degrees starting out in the sun or warm engine, compressor off. If I can get 30 degrees under ambient, I'm close to good to go.

40 degrees F would be perfect. I had one car with gas input right next to compressor. Had to be careful. Heard about compressors locking up. I typically use the 10/2 rule. Up ten seconds, upside down two seconds. Some or most systems now turn compressor off if undercharged, or overcharged, or if sufficient evaporator temperature has been reached.

Greg

Reply to
gregz

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