Ok, I've been a wrench for years, but A/C is something I know little about and have only been working into it for the last few years, never had any formal training with it, just a bit of education from others. I have a couple of troubleshooting questions that I hope someone with experience can help me with. First machine, actually several this has happened to. The system would work flawless at start up. High and low side pressures are good, within the proper ranges. System has a full charge of R134A, no bubbles in sight glass. Evaporator not clogged externally, blowing hard stream of air, air is good and cold. But after running for 10 - 15 minutes, low side goes into a dead vacuum, high side stays up. It was my theory that system had moisture in it and the moisture froze in the expansion valve effectively blocking it. Perform a recovery of the system, fit a new filter/drier, and do a two hour evacuation. Re-charge system, all things now work proper. My question; in this case, was diagnosis correct, was moisture in the system the likely culprit? The latest one I'm working on is a Bobcat 442 excavator. Full charge of R134A, no bubbles in sight glass, compressor remains on, not cycling. High and low side pressure is in normal ranges, low around 30 - 40, high around 250 - 275, doesn't really fluctuate. Air blows good through evaporator. But it's not blowing good cold air, just cool at best. I plan on doing a recovery on the system and fit a new filter/drier, but should I remove the expansion valve and check it out? This one I'm really not sure what to do with.
willie im in the same boat as you and learning as i go thats what i would check does it have an orfice tube?also i am on a website http://www.acsource.net/acforum/index.php?sid=6913bdd4781d3c0be1b7b80b32f7ca1c it may not have the particular machine you are working on but i would think the troubleshooting would apply.
Willie I'm n expert but any time I break open the system I replace dryer and expansion valve are orifice tube.I see you checked the evaporator.I had an operator argue with me about that said the compressor was bad.I cleaned the evaporator and it worked fine.I taught myself.Baught a book and praticed.Learned never to patch a unit that had a good many hours on it.If the compresser comes apart you have to flush the system real good.
I am still in training for A/C work, Ive been going to the school of hard knocks, for 8 years on A/C. I have never heard or seen the first problem What I do have to say on the second issue is, put a fan in front of the condenser, I usually use a shop fan and see if that helps Does it have a thermostat switch in the system, they are usually around the expansion valve Is the line going to the expansion valve, cold on each side of the valve? If not change the valve, or at least tap on it and see if that helps Im not familiar with the Bobcat, but does it have a filter (like a house filter) I had a Cat that had a washable air filter and it stopped up and it wouldnt cool correctly. Good Luck
I plan on digging into the air box first of the week and take a look around in there, not sure what components are in there at this point. Most Bobcat stuff I've worked on uses an expansion valve. I would consider replacing the expansion valve, but, this is the unit that has a simple little receiver/drier that Bobcat wants 540 bucks for, I could only imagine what they want for an expansion valve. Now that's an interesting tid bit of info. Thanks.
Hey it's only money.Man needs to stay cool.Funny no one thinks a mechanic needs to stay cool.They usually break down in the hottest part of the day.Need it going now and park it in the open no shade tree.
Willie, on your first problem I'd say your diagnosis was correct. I recently had the exact same problem on a 973 Cat track loader, replaced the dryer and re-charged system and all worked as it should.
Slightly off topic but does anyone use BBQ gas otherwise known as High chill? I have swapped a few bits of gear over to it and seems to outperform R134a hands down. Also happens to be a lot cheaper too.
Interesting, BBQ gas like propane?
A hugely controversial idea with lots of propaganda about safety issues on both sides. I did it just once, more out of curiosity than anything. I wouldn't use anything but actual refrigerant today and it's what the the systems were designed for. I did it on an old pickup truck right out of a propane torch bottle and it actually worked very well.
I'm just glad that ammonia as a refrigerant is no longer the norm. I busted into the cooling lines of an old refrigerator once, stuff sent me on the run in jackrabbit mode. :tong
I asked an air conditioning tech one time why the old refrigerators lasted so long. I mean my mom's old basement fridge is from 1954, is still very cold and has never been charged. He said one reason besides the build quality was the ammonia refrigerant, the molecules are so large the gas doesn't get out so easy.
Yep, NH3 Ammonia is a very good refrigerant, still used in many applications like ice making companies, it's just not very "user friendly". If you ever get a whiff of NH3, it will take your breath away. Just take care working around old refrigerators and don't knock a hole in the system, that stuff will cause immediate evacuation of the house or area.
I would say your diagnosis is spot on. It could also be a chunk of crud from a previous compressor replacement that plugs the orifice. If I have to replace a compressor i flush the whole system.
willie59 i have many years on ac work! i think you was right on on your first problem. the 442 i need a little more info. there could/should? be a filter for the evap coil. Is the line on the evap side of the expansion valve cold? if yes the expansion valve is letting freon through it. if its warm replace it. also ck the condenser if it cant get dissipate the heat it wont cool
I will be working on the unit tomorrow (hopefully), will dig into the air box and check expansion valve operation. The condenser is one of those installations that sits maybe 1 1/2" from radiator, I did block side openings around condenser and monitored high pressure, it didn't drop any which indicates condenser is working sufficiently. Maybe this thread will become an A/C troubleshooting thread, would be good with me, it would be good to have a shop thread about different problems and remedies associated with A/C systems.
head pressure seems kind of high for 134 coul be slightly over charged ,remember head goes down- -suction goes down = colder evap.also make sure evap compartment is sealed good warm air infiltration will ruin suction and raise head pressure. when in doubt check super heat that will tell you if you have an obstruction in orifice or cappillary restrictive device.
Thanks for the info PROBIKE101. On this unit, I charged the R134A only until there were no bubbles in the sight glass of receiver/drier, that's when I cut if off and said "hmm". Not likely this one is suffering from overcharge.
We have a lot of trouble with AC systems that have long runs of rubber hose running R134a and the High Chill is much better in this environment I presume to a larger molecular structure. Any of the systems that have mostly metal plumbing seems to retain its gas a lot better.
I think a lot of the propaganda on the against side might be dupont not wanting to let market share go on their patented gas. I havent found it bad on anything as it runs at a lower pressure (only have to use a third of the amount compared to R134a ) and as far as being dangerous well no one seems to worry about the fuel tank or lpg tank under their car too much.. Anyhow Ill bugger off now and let people get back to the topic at hand. Cheers.
Oh I agree with you, I think the safety issue was way overblown. Really Freon and a flame makes a poison gas and nobody worried about that much. The commercially prepared propane blends would be better than just straight propane, I think they add a few percent of butane and other bits.
Reminds me of when I was just out of high school working as a motorcycle mechanic. I wanted a compressor and busted an old fridge open behind the shop which happened to be sitting directly under the large building fan to keep the shop cool. I didn't know about the ammonia thing back then and it sure emptied the building out in a hurry.
LMAO! I bet ur eyes popped out like a stomped on bullfrog. :lmao
didyou fix it?
Supposed to get a new receiver/drier tomorrow morn so I can continue on with repairs. But I didn't order the $540 unit from Bobcat, local parts store getting a replacement for about 20 bucks.
does original bobcat reciever have a sight glass?
Yep, sight glass and binary pressure switch
binary? is that brand name?
A two pole pressure switch, sorry.
bouble pole single throw?
willie is the sticker still there that has the total charge amount in #s or kg? if so get a set of electronic scales and weigh the charge. more accurate than the sight glass. and some systems are that sensitive!
It annoys me how they use stickers on gear that they should know gets pressure washed ect. Why cant they engrave or stamp it or at least use a decal that wont come off. Makes it hard when you have to work out for yourself how much gas should go in.
Hmm, didn't know that. But then, there's a heckuva lot I don't know about A/C. Nope, no sticker on it to indicate required charge. I did get started on it today, then had to leave to work on a rental unit. I fitted a new receiver/drier, did a 2 hr evac, fired it up and gave it a charge until the sight glass was clear. High pressure was around 250 when I had to leave. Unit was blowing slightly cooler than it was previously. I did check the line at expansion valve, line was warm prior to expansion valve, got cold after passing through valve. I did weigh my tank before starting to know how much it used, but day was over before I could get back to it, hope to finish up tomorrow.
The service manual is another place that should tell you the charge weight. It really is the most accurate way to do it. In some systems you can still get bubbles in the glass even with a full charge.
I'd be thinking there isnt enough gas in there, remember when the bubbles arent visable (on a traditional system) the receiver dryer isnt full of liquid, you need to get enough gas in there to ensure the unit is 2/3rds full in operation doing it only by measuring the gas on the way in isnt to best way to get the most out of your a/con with high ambient temps as for LPG in a/con systems it should be banned IMO there has been afew incidents over the years with people being burnt from using this in a/con systems, most of the drive into this type of gas is from the companies selling it, afew states of Australia have banned its use in automotive a/con systems
Yep, I charged it until there were no bubbles, used 20 oz. Then after reading these posts, I called Bobcat, service man said it took 2.2 lbs, which means I needed to add an additional 12 oz.
so when you added the extra did it make it work?
Had a machine that wouldn't cool. Had low pressure on high side and HOT! discharge line. Changed compressor and sure enough found gray sludge in system. Flushed out lines and condensor. Tried to flush evap core, but couldn't get flush to go in. I am assuming the expansion valve was closed and wouldn't let it through. Added some oil and dye after vacuuming for 1.5 hours. When I started, the high side was low (100) and low side was high (80) with only one can in it and compressor turning. After awhile all of a sudden high side went up and low side went down and I finished charging (three cans). Cooled great. After running for an hour the high side kept creeping up (ended up at 450) so I took some out and it seemed ok. Sent to customer and after a day of running high side had spiked again. let more freon out and it worked again. My question is, why is it when you start it up in the A.M. and the pressures are almost too low, but it does cool, but as the machine heats up the pressures go up and it took such little amount of freon? This is on a 140 size excavator.
ambient temperature caused head to go up, sounds like exspantin valve is stuck in 1 spot you are adjusting charge to it not it adjusting to your charge
Lots of oil and more of the gray sludge was most likely in the evaporator as the evaporator is a major collection point. The only way to properly flush a system is at the component level, but yes, it can be a pain in the arse. If the gray sludge is from a bad compressor your new one might take a dump also. You missed a good opportunity for troubleshooting by not weighing in the charge.
Yep, gotta take the expansion valve out of the flush process, it won't let you flush the system proper. You have to disconnect the lines going to and out of the expansion valve.
134 a sucks....................plugs every thing up i believe it happens when the oil over heats along with moisture and non condensibbles.
Hey, Willie59 I forgot-- I'm an A/C expert. I don't know what all the fuss is about regarding parts prices--especially all the fussing about Bobcat parts. I worked out in the 95 degree heat today, was thinking about y'all who work in the heat. My Bobcat 773's A/C cost $9.95 at Walmart or Autozone, and only takes about 30 seconds to replace the entire system if it quits. I don't have a good picture of it but it works sorta like this: :shf lol
lol
Sight glasses are not accurate with R 134A and should not be used for charging.
we had a really switched on guy who took us through our a/con course, he had spent 20 years in and around it, some sort of engineer he can't advise enough at how dangerous it is he showed us a video (for the life of me i cant find it on the net) but it was produced by a major propane manfacturer and conducted by a university which they were to basically show how safe the gas was, the first half was them conducting small tests and showing figures on the chalk bourd how you could leak out the contents of the system in a cars cabin and it wouldnt ignite to lobby the NSW and other governments in Australia to let the gas be available for use in a/con systems then they did a full scale "test" where the guy let off two cans of gas into a cars cabin with the windows closed (i think it was around 250g) and then proceded to light a match while sitting in the passengers seat while the camera's were rolling!! blew all the windows out of the car covered the film crew in glass, there was a guy on the outside of the passenger side front window who got his face cut pretty bad and the guy inside the car (who was the "brains" of the production) was left without much hair on his face and burns to his hands
Case CX210 excavator, A/C is working, but not quite right, rip the inside of the cab apart. Well well, now that's a problem. So much dust build up on the face of the evaporator it's turned into a 1/4" layer of mud.
Looks like it turned into cement from freezing up all the time the fan blade cant be much better............lol
LoL, not quite cement yet, I stuck my finger in there, felt just like sticking your finger in mud.
What's the problem here?....I still see a few open holes
no problem from what i can see............................lol, this customer has the best maintenance agreement known to man, bring it too a mechanic .................pay as you ******k it up agreement ,lol
No refrigerant is particularly safe. R134A is toxic if inhaled and this is from the MSDS of R134A: "R-134A is not flammable at ambient temperatures and atmospheric pressure. However, this material will become combustible when mixed with air under pressure and exposed to strong ignition sources. Contact with certain reactive metals may result in formation of explosive or exothermic reactions under specific conditions (e.g. very high temperatures and/or appropriate pressures)."
I disagree....R-134A is one of the few "pure fluid" refrigerants left on the market...like R-12, R-22, R-502 (not blended like most CFC replacement refrigerants are today) so it will not "separate and flash" the sight glass like blended refrigerants are rumored to do, and being its a pure fluid refrigerant, its one of the few left that can be charged as a vapor or liquid.
why does bottle say on the side to charge upside down that wood be a liquid charge.....................no
That would be a liquid charge....but liquid charging is only supposed to be done from the high side access port....you should never charge an AC system with pure liquid refrigerant. The compressors job is to "compress" refrigerant vapor coming from the Low side. The compressor is not designed to compress liquid (liquid slugging) and can be damaged or destroyed if too much liquid is put into the low side.
Another thing about 134A is that the oil used in automotive 134A is polyalkylene glycol (PAG)...The oil used in Commercial 134A is Polyol ester oil, (commonly called POE)....Both of these attract moisture like a prostitute attracts politicians....and hold it a LOT longer.....it is not like the old mineral oil R-12 used....so never leave the system open when not servicing...IT IS NOT FORGIVING!... It takes a lot longer to get the moisture out of these systems.
I take your point, its not 100% safe, neither is most chemicals in a workshop but I would suggest LPG would ignite alot easyier than R134A, MSDS's tend to dramatise to a "worst case" occurance I know which one i wouldnt want in my car, you have to look at the world wide automotive industry if it was safe, cheap and a better quality gas then why wouldnt manufacturers use LPG as a factory fill in their systems?
i have to disagree with a clear sight glass and 134. i have converted my 3 older chry. products and if one clears the sight glass they will NOT cool. used a digital thermo taped to the suction line. gassed it to the coldest point and then added until it started warming then discharged back to the coldest point and all 3 work good one of them really cools better than the 12 that was in it.
That's a neat trick jughead, I never thought of monitoring suction line temperature. I suppose you're referring to the suction line where it connects to compressor. I wonder if you could get the same results using a digital lazer temp gun, I suppose it would work as well.
called super heat
thank u willie i put it next to the evaporator. PROBIKE i have read and re-read super heat stuff and i still dont understand it. i am not a pro though just self taught old country boy. didnt want to leave any different impression
basically you are measuring tempchange at the end of evaporator and suction inlet at the compressor to cold ,to much flood back of refridgerant,to warm compressor over heats an dies.use your gauges and convert presure of your refrigerant to temp on blue gauge.hook temp probe to suction big line,on inlet of compressor and subtract both temps that will be super heat. about 12 degrees to 22 degrees is a good super heat .on adjustable exspantion valves adjust valve ,on non adjustable restrictors open orifice or lengthen or shorten cappilary tube or more or less charge,compressors are cooled by the return vapor from the evap,this is the best way to diagnose any air conditioning system or refridgeration system,no super heat no charge or bad compressor ,not enough suctionorn not enough discharge pressure,or lastly a restiction or partial restriction which will show as no super heat and verylow suction on blue gauge and low discharge on red gauge due to a restriction.
only adjust the expansion valve after u have MADE SURE it is charged correct & u have ruled out other causes. the expansion valve hardly ever goes bad, but gets blamed/changed to often as the problem, that is still there after it gets replaced!
its the best way to charge, if you use a temp probe on the outlet of the evap, charge the system with the fan speed on low you can get to a good charge when the your running about 4degreesC but the trick is to then open the cab window and put the fan speed on high and pop some more in to get the suction line down to the same temp, then pop in a safety charge to fill the dryer if its a coldish day (10-15% of total capacity) but keep and eye on the high side gauge when you bleed it in and stop if the needle starts to spike you can charge a system without knowing the weight required, its about reading when the system is full and knowing when to stop
very well explained :thumbsup
thanks..............ihave my moments