Do we have any A/C experts here?

[willie59]

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.

 

[bobin35]

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.

 

[2stickbill]

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 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.

 

[Willis Bushogin]

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

 

[willie59]

Willie I'm n expert but any time I break open the system I replace dryer and expansion valve are orifice tube.

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.

Is the line going to the expansion valve, cold on each side of the valve? If not change the valve,

Now that's an interesting tid bit of info. Thanks.

 

[2stickbill]

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.

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.

 

[cb75]

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.

 

[nextdoor]

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.

 

[CM1995]

Slightly off topic but does anyone use BBQ gas otherwise known as High chill?

Interesting, BBQ gas like propane?

 

[Komatsu 150]

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.

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.

 

[willie59]

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

 

[Komatsu 150]

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.

 

[willie59]

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.

 

[Dualie]

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.

 

[FSERVICE]

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

 

[willie59]

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.

 

[PROBIKE101]

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.

 

[willie59]

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.

 

[nextdoor]

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.

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.

 

[nextdoor]

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 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.