evaluating an AC compressor when system is currently discharged - Page 2 - PeachParts Mercedes-Benz Forum

vstech · #16 04-28-2018, 12:09 PM

The vacuum pump should not be connected to a system until after it is leak free.

BillGrissom · #17 04-28-2018, 12:34 PM

When I have had a compressor on the bench, I verify it at least tries to pump by turning the shaft by hand and verifying I feel suction on my thumb at the inlet port and it builds pressure when blocking the outlet port. You could do the same on the car, and even let the engine turn the compressor - just jumper the AC clutch by removing the relay (driver's side inner fender) and jumpering terminals 30 to 87 on the base.

The hose rubber can be replaced by you. Cut off the factory crimps and secure new hoses w/ Oeticker stepless ear clamps, or new ferrules if you have a MasterCool crimper like I do. All can be bought on ebay. Only use newer "barrier hose" for less leakage. I preferred the "reduced" sizes.

I use hydrocarbon refrigerant in all my vehicles (even 2002 minivan). It works slightly better than R-12 and costs much less. R-134A is being discontinued and the PAG oil absorbs moisture to cause corrosion. PAO 68 is the best oil for all refrigerants.

97 SL320 · #18 04-28-2018, 06:23 PM

Quote:

Originally Posted by BillGrissom

The hose rubber can be replaced by you. Cut off the factory crimps and secure new hoses w/ Oeticker stepless ear clamps,

Not always. Some AC fitting tubes are smooth / near smooth for easy hose assembly and the ferrule is locked / crimped to the fitting with the shape of the crimp mimicking a " barb " or " rings " , this prevents hose blow off.

Hydraulic hoses fittings are built this way as well.

Old style field install hose fittings have barbs to prevent hose blow off when used with a screw clamp. " AC " spec hose clamps have a leg that gives proper spacing so pressure is applied to a smooth area just past the barb. Standard non leg clamps are fine if the spacing is properly set.

When replacing factory ferrules with crimped on ones, be sure that the ferrule is crimped to the notch on the fitting.

Quote:

Originally Posted by BillGrissom

I use hydrocarbon refrigerant

RE: R290 = " propane "

From Lindie a major industrial gas supplier.

R290 (CARE 40) Propane | Linde Gas

Quote:

It is a flammable refrigerant and therefore not suitable for retrofitting existing fluorocarbon refrigerant systems.

MSDS / SDS sheet.

http://www.refrigerants.com/pdf/SDS%20R290%20Propane.pdf

Quote:

2. HAZARDS IDENTIFICATION

CLASSIFICATION:
Flammable Gas, Gas under pressure, Compressed Gas

SIGNAL WORD:
DANGER

HAZARD STATEMENT(S):
Extremely flammable gas, Contains gas under pressure, may explode if heated

SYMBOL(S):
Flames, Gas Cylinde

I would not use R290 in a mobile application, propane would be hazardous in a crash that punctures the system. It would be fine in a household fridge, the chances for a sudden leak are low and the system volume small compared to a car.

ROLLGUY · #19 04-28-2018, 08:01 PM

Quote:

Originally Posted by 97 SL320

Not always. Some AC fitting tubes are smooth / near smooth for easy hose assembly and the ferrule is locked / crimped to the fitting with the shape of the crimp mimicking a " barb " or " rings " , this prevents hose blow off.

Hydraulic hoses fittings are built this way as well.

Old style field install hose fittings have barbs to prevent hose blow off when used with a screw clamp. " AC " spec hose clamps have a leg that gives proper spacing so pressure is applied to a smooth area just past the barb. Standard non leg clamps are fine if the spacing is properly set.

When replacing factory ferrules with crimped on ones, be sure that the ferrule is crimped to the notch on the fitting.

Agreed. Removing the old rubber and ferules and then clamping on new hose (must be metric) with any kind of clamp will allow the hose to blow off. This is especially true when using 134a, as the pressures are higher than R12 or Hydrocarbon refrigerants. I use new steel beadlock fittings in all the hoses I make. If I am using a factory metal manifold or pipe, I have a barb welded (brazed) on, and crimp my own hoses on.

kuene · #20 04-30-2018, 12:00 PM

Getting deep and heavy - I like it. I feel confident that I can't get better advice and quality knowhow on AC anywhere else.

Question - I know there must be a good answer to this but I'm curious - why can't one pressure test with just plain air instead of nitrogen? I understand you don't want to introduce moisture - but if the system is empty/open and you are going to replace the receiver drier and vacuum soon after - is there some really clear reason one can't use compressed air? I've seen youtube videos of this - but of course the comments are just a bunch of people screaming at each other.

Where does one regular joe like me get nitrogen, is it expensive?

marco5 · #21 04-30-2018, 04:30 PM

Go to a A/C shop dude, they will have all of the tools to test, pressurize the system and such. If you're gonna do the work yourself, do this.

1) Vacuum the system for 30 min.
2) Charge it with a few A/C cans (make sure it has OIL and DYE, do not charge it with JUST freon) run the A/C until for a while.
3) Drive with it on and etc.
4) Then check for leaks after a few hours with UV glasses, determine where the leak is (probably the compressor)
5) vacuum the system once again and fix leak for an hour (most likely involves replacing compressor) also replace your drier, expansion valve (very important). This is where you do the conversion to r134a
6) vacuum again, see if it holds vacuum for an hour if it holds, charge A/C

Rooster300SD · #22 04-30-2018, 04:52 PM

Getting ready to do this.
When you pressurize with the nitrogen does it matter which port
you hook it up to? Won't the pressure fall overnight do to the cold?

Thanks,
Jeff

kuene · #23 04-30-2018, 05:48 PM

OK "Dude" I'll just follow this authoritative and comprehensive 6-step process and I'm sure I'll be in business!

Quote:

Originally Posted by marco5

Go to a A/C shop dude, they will have all of the tools to test, pressurize the system and such. If you're gonna do the work yourself, do this.

1) Vacuum the system for 30 min.
2) Charge it with a few A/C cans (make sure it has OIL and DYE, do not charge it with JUST freon) run the A/C until for a while.
3) Drive with it on and etc.
4) Then check for leaks after a few hours with UV glasses, determine where the leak is (probably the compressor)
5) vacuum the system once again and fix leak for an hour (most likely involves replacing compressor) also replace your drier, expansion valve (very important). This is where you do the conversion to r134a
6) vacuum again, see if it holds vacuum for an hour if it holds, charge A/C

97 SL320 · #24 04-30-2018, 07:55 PM

Quote:

Originally Posted by kuene

Getting deep and heavy - I like it. I feel confident that I can't get better advice and quality knowhow on AC anywhere else.

Question - I know there must be a good answer to this but I'm curious - why can't one pressure test with just plain air instead of nitrogen?

Compressed air would be fine in a pinch if it was completely dry, getting completely dry air is the difficult part. Compressed bottled nitrogen is dry making it convenient. For the DIY guy, use R132 since it is convenient and won't harm R12 system. A nitrogen bottle ( of various sizes ) can be rented from a welding supply place but that gets to be more $ than a can of R132.

Pulling a vacuum on a system is a valid first test for leaks. If it can't hold a vac for a few minutes, there is a large leak.

97 SL320 · #25 04-30-2018, 08:01 PM

Quote:

Originally Posted by Rooster300SD

Getting ready to do this.
When you pressurize with the nitrogen does it matter which port
you hook it up to? Won't the pressure fall overnight do to the cold?

Thanks,
Jeff

As a matter of good practice, always introduce any gasses into the low side. If the compressor is running, trying to charge from the high side can result in a tank / can failure.

It is OK to vacuum the system from the high and low however.

The pressure will drop slightly as temps drop, but it will go back up as temps rise. Think about how tire pressures change due to temp and expect the same variation on the AC system.

kuene · #26 04-30-2018, 08:22 PM

Ok. I’ll leak test with r134.

Going to next search for exactly how I’m supposed to reclaim the 134 that I’ve put in system for leak test...

Also, I might as well just replace the expansion valve and also put new seals on the compressor (assuming it works). Right?

ROLLGUY · #27 04-30-2018, 09:11 PM

Quote:

Originally Posted by marco5

Go to a A/C shop dude, they will have all of the tools to test, pressurize the system and such. If you're gonna do the work yourself, do this.

1) Vacuum the system for 30 min.
2) Charge it with a few A/C cans (make sure it has OIL and DYE, do not charge it with JUST freon) run the A/C until for a while.
3) Drive with it on and etc.
4) Then check for leaks after a few hours with UV glasses, determine where the leak is (probably the compressor)
5) vacuum the system once again and fix leak for an hour (most likely involves replacing compressor) also replace your drier, expansion valve (very important). This is where you do the conversion to r134a
6) vacuum again, see if it holds vacuum for an hour if it holds, charge A/C

kuene:

Quote:

"Go to a A/C shop dude, they will have all of the tools to test, pressurize the system and such."

This is good advice.

The rest (below the above quote) is WRONG in so many ways. Please do NOT follow marco's advice. There is so much good A/C information on this forum, and most of it comes from seasoned professionals. First: NEVER use vacuum to check for leaks!!!!!! This has been said so many times, and so many ways. Second: It is illegal to vent refrigerant! If you know you have a leak, why would you WASTE refrigerant by using it to check for a leak??? Yes you can use compressed air for finding a leak in a system that will be opened up soon anyway. After that, you SHOULD flush the evaporator and condenser before replacing any parts. Please follow the advice of members like Leathermang, Vstech, etc. Also read their A/C threads, you will learn the proper way to service your system. Thanks, Rich

marco5 · #28 04-30-2018, 10:02 PM

Agreed, I'm a noob with A/C systems lol. Sorry for the wrong/incorrect advice.

Go to a AC shop

Quote:

Originally Posted by ROLLGUY

kuene: This is good advice.

The rest (below the above quote) is WRONG in so many ways. Please do NOT follow marco's advice. There is so much good A/C information on this forum, and most of it comes from seasoned professionals. First: NEVER use vacuum to check for leaks!!!!!! This has been said so many times, and so many ways. Second: It is illegal to vent refrigerant! If you know you have a leak, why would you WASTE refrigerant by using it to check for a leak??? Yes you can use compressed air for finding a leak in a system that will be opened up soon anyway. After that, you SHOULD flush the evaporator and condenser before replacing any parts. Please follow the advice of members like Leathermang, Vstech, etc. Also read their A/C threads, you will learn the proper way to service your system. Thanks, Rich

vstech · #29 04-30-2018, 10:13 PM

Ac work is very easy if you follow a few rules.

#1. Do everything you can to prevent moisture from entering the system. (Air has a LOT of moisture in it)

#2. Pressure testing is the best way to check for leaks. Vacuum testing without a digital micron gauge is just wasting time. Vacuum changes the direction seals are designed to function, rendering the test invalid, plus, if it leaks enough to show a leak, you just broke rule #1...

#3. A leaked mobile system has lost an unknown amount of oil... it is best to flush all components, and add the correct amount of oil to the system spread around to the components as the manual advises... replace all o-rings, and pressure test for leaks, then replace the dryer and evacuate.

#4. Charge from a tank of refrigerant as a liquid into the high side of a non running system by weight, then charge with gas to get the charge precise. (Using cans to charge from a vacuum gets a lot of air and moisture ingested into the system ...Rule1)

BillGrissom · #30 04-30-2018, 10:13 PM

For those interested in repairing their hoses, read my post Fixed AC Hoses 1985 300D . I since replaced all hoses in my 1984 300D too (exc. small liquid hose in both). The suction fittings had no barbs (see photos). The H.P. hose has smooth ripples, as I recall, but might be confusing w/ the oil cooler hoses which I similarly fixed. I tried to align the crimps in the ferrules w/ the dips in the fittings.

Oeticker clamps work fine. I used one on the H.P. hose at the R4 compressor when I thought my ferrule clamp was leaking, so cut it off on the car and used the Oeticker since I didn't want to remove the whole hose (can only use crimper on bench repair). Turns out the fitting wasn't leaking, rather the tube had a tiny leak from bending it w/ wrench to fit the Sanden compressor I installed (w/ Rollguy's bracket kit).

Re HC refrigerants, no need to roll-your-own. I have used Duracool for decades. Another is Enviro-Safe. Many crazy stories of "might explode", yet no fires in millions of cars that have used it for years. I may be the only one who ever tested, pouring some liquid on the ground and lighting it - just a very weak flame like a candle. R-134A produces deadly phosgene gas when it burns, if you want to worry about something. All refrigerant leaks can ignite - if not the refrigerant the fine oil spray burns. Amazing, that is how a diesel works.