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Kenworth Did Not Hold All Vacuum Overnight Pages: 12

Shepherd777 on Wed November 09, 2011 10:41 AM User is offlineView users profile

Year: 2003
Make: Kenworth
Model: T2000
Engine Size: ISX
Refrigerant Type: 134a
Ambient Temp: 60
Pressure Low: n/a
Pressure High: n/a
Country of Origin: United States

Hello All -

When I left my shop last night, I had 28 inches of vacuum after evacuating for an hour or so.

I closed both gauge valves before I left the shop yesterday, and turned off the pump. When I returned today, vacuum was down to 10 inches or so.

I started my 6 CFM pump, opened both valves, and it is back up to 28 inches now while it is running.

Do I definitely have a slow leak, or was the vacuum just boiling off more moisture overnight in this relatively large system?


JACK ADAMS on Wed November 09, 2011 1:20 PM User is offline

This will all depend on what service was performed.. You don’t say why you had to pull a vacuum on it. Anything could be the cause, another leak, bad gauge connections or all of the above. More info please…

Shepherd777 on Wed November 09, 2011 2:26 PM User is offlineView users profile

Hi Jack -

New compressor, new refrigerant lines, new drier, new condenser.

No previous failure. Just a show truck with mostly new A/C parts.

It is definitely maintaining the vacuum for over the 10 minutes stated on the Auto A/C Evacuate and Charging Procedure as stated on this web site.


JACK ADAMS on Wed November 09, 2011 2:46 PM User is offline

Never really been a big fan of leaving gauges on over night for this reason. Can drive you nuts at times, we did this with a few cars/trucks just to find that the gauge couplers leaked but not all the time. Just depends on the manufacture of the service ports on the hoses of the vehicle. Allot of the stuff that sits on the shelves at the local parts store are made overseas and are suppose to be at OEM specifications.

We use the same parts we offer to our customers and this happens from time to time, we may not know how well it is built to the OE specs but we do let our suppliers know what works and what don’t every chance we get.

Good luck, and hope you find your leak if you have one.

Shepherd777 on Wed November 09, 2011 5:35 PM User is offlineView users profile

I have almost new MasterCool gauges (used twice before) that I bought from this forum's sponsor, ACKits.

There are two new Eaton Aeroquip charge ports are installed in-line in new Aeroquip refrigerant hoses.

So I may have a leak in the system, or I may not???

Per TRB's Evacuating and Charging Procedures in the Procedures, Tips, and FAQ section of the forum he states:

"When system has achieved a state of 29.9 hg’s of vacuum close both dials on the a/c gauge set. You may loose up to 1 hg for every 1000 feet above sea level depending on the capacity and quality of pump. At this point wait 5 to 10 minutes letting the vacuum boil off any moisture trapped in the refrigerant oil. This is also a good time to watch and see if vacuum has returned to a zero state. If so you need to check for leaks in the system. Assuming the system is holding a vacuum after letting the moisture boil off repeat the evacuation procedure again. This process may need to be done a few times before all moisture has been removed and you see no degradation in vacuum after closing both dials for 5 to 10 minutes."

So is 5-10 minutes, as stated above, sufficient to determine if there are no leaks?

Am I good to charge the system if it holds for 5-10 minutes, which it does?

Or would a perfect system with perfect gauges and ports hold a vacuum overnight or even possibly indefinitely?

Does a vacuum degrade over time, but pressure (refrigerant and oil) not diminish over time without a leak?

Any other opinions?

Edited: Wed November 09, 2011 at 5:44 PM by Shepherd777

JACK ADAMS on Thu November 10, 2011 10:53 AM User is offline

My suggestion would be to charge it to the OE specs and run for 15mins and then leak check it. If nothing is found then let sit for 20mins and leak check again. In the type of environment that you are in as well as the size, moisture may not be at its boiling point and may need a double vacuum prior to charge. Vacuum down for a good hour, shut down for half hour and then evac for another half hour. This will help boil out any moisture that may still be in the system.

Hope this helps and good luck..

Dougflas on Sat November 12, 2011 8:14 PM User is offline

If you don't have a micron guage hooked up, your vacuum time is a crap shoot. With POE oil, you probably have moisture trapped in the oil. Pull a vacuum for a few hours min and warm up the engine with compressor unplugged. Also, make sure you have a new drier installed. If possible, pull an overnight vacuum. If you were to use/see a micron guage on a system, you'd have a different opinion when someone says to vacuum for an hour or two. In oreder to evacuate and hold 500 microns, you will have to pull a vacuum for 8 to 12 hours.

NickD on Sun November 13, 2011 6:15 AM User is offline

Vacuum is a negative 15 psi pressure that can pull in service port valves and the compressor seal that only seal good with a positive pressure. One good reason why your AC system worked fine in the fall, but when sitting outside in -20*F temperature, the refrigerant pressure drops to nothing relieving that positive pressure so it can leak out. Hey, we didn't design this, just have to live with it.

Good get a reasonable seal with R-12 Scharder valve ports, can't blame the gauge manufacturers for these crazy quick coupler R-134a ports, they have to follow the law. But even the EPA is somewhat reasonable in this respect, let you waste a can of R-134a to check for leaks, or holding static pressure at the same given temperature overnight.

Proper way to charge is to run the pump, and have the ability to switch over to charging instantly without moving any hoses, and hope it holds pressure after doing a neat installation. O-rings are also a PITA.

Shepherd777 on Sun November 13, 2011 9:24 AM User is offlineView users profile

Thanks for all the replies.

Dougflas - I am using SP-15 oil, if that makes any difference. I pulled a vacuum for a few hours yesterday. I'll check how well it held when I return to my shop tomorrow morning, 44 hours after closing the valves and shutting off the pump. If the vacuum is low when I arrive in the morning, I'll run the pump overnight. I have a new compressor, new condenser, new drier, all new refrigerant lines forward of the firewall, new in-line service ports, and new o-rings forward of the firewall and at the rear evap. There are OEM hoses going from the front evap to the rear evap in the bunk, and OEM evaps.

NickD - "Vacuum is a negative 15 psi pressure that can pull in service port valves and the compressor seal that only seal good with a positive pressure." That is exactly what I argued to my buddy who visited my shop yesterday. Just because it's leaking a vacuum, doesn't necessarily mean it will leak under pressure. The system is designed not to leak under pressure, not a vacuum.

I was gonna hit the auto parts store this morning and buy a can of virgin R134a with dye, install it and look for leaks. I have a 75 watt, 110 volt black light. I figure that will work better at finding the dye, if there are any leaks.

Edited: Sun November 13, 2011 at 9:25 AM by Shepherd777

Shepherd777 on Sun November 13, 2011 11:10 AM User is offlineView users profile

Okay, the parts store did not have any R134a that had dye without sealer. So I scratched that idea.

I did buy a 1 ounce bottle of "Universal A/C UV Dye"

The directions say to add 1/4 ounce of dye before oil is added, but the oil is already in the system. Can I just pour 1/4 of the bottle into an open line, evac again, add 1 bottle of R134a, and then test for leaks?

And this is a very large 2 evap system. Should I add more than 1/4 ounce or will 1/4 be enough to find leaks, if any?

Thanks again.

Dougflas on Sun November 13, 2011 5:13 PM User is offline

You can pour the dye into the system but it will not indicate until the system has been run a while because the dye must mix with the oil. The oil will have to migrate thru the system with the refrigerant and that will take some time. New comprssor's seals can seep at first. That is the reason for turning the compressor by hand; you're trying to seat the shaft seal. If you open the system while it's under a vacuum, you will draw moisture into the system. You are at a catch 22 situation right now. If you open the system, moisture will enter. If you charge the system and have a leak, you will need a sniffer to find it. My advice is to add some R134 to give the system positive pressure. Then find a source for R134 with dye ONLY. Then charge the system to full capacity and then see how it does. If it leaks down, you'll have dye in it to hopefully find the leak. Be aware some leaks do not show up with dye.

Shepherd777 on Sun November 13, 2011 5:57 PM User is offlineView users profile

Thanks again Dougflas -

I'll just see where the gauges are in the morning and if low, I'll pop it open and pour in some dye. It's no biggie if I have to evac it again. I'll let the vacuum pump run overnight after I dump in the dye. I'll charge it up on Tuesday and hope the pressure stays. If not, I'll turn on the UV light.

Will 1/4 ounce be enough for a 4 pound, 2 evaporator system???

mk378 on Sun November 13, 2011 11:41 PM User is offline

Dye is carried by the oil, so the real question is how much oil is in the system. If it's 16 oz or more, go up to 1/2 oz of dye. The system must be fully charged and running for dye to work. When stopped, often only clear refrigerant gas will escape from leaks.

If you have time, put a small charge of refrigerant in without running the compressor; use enough to get a pressure of about 50 psi on both sides. Then disconnect the manifold and put the caps on the ports and walk away for a day or two. Come back and measure the pressure, if it hasn't dropped much there is no big leak and you can go ahead and charge the rest of the way. If it's leaked down to near zero, need to find the leak. An electronic leak detector is the best tool for that situation.

Edited: Sun November 13, 2011 at 11:46 PM by mk378

Shepherd777 on Mon November 14, 2011 10:43 AM User is offlineView users profile

Well, I think I might have found the culprit.

When I removed the gauge connector from the brand new Aeroquip EZ-Clip low side service port, I heard a leak.

I put my finger over the port and the air stopped leaking into the system. Never thought of tightening those damn schrader valves before installation, since the ports are brand new. The only problem now is I don't have a tool at my shop to tighten them. So it's back to the auto parts place to buy one.

mk378 on Mon November 14, 2011 1:48 PM User is offline

Like the others said, shrader valves aren't designed to hold against vacuum. To prevent air from leaking in, the manifold hoses must stay connected to the service ports for the entire time the system is under vacuum.

Edited: Mon November 14, 2011 at 1:49 PM by mk378

Shepherd777 on Tue November 15, 2011 1:17 PM User is offlineView users profile

Thanks mk378.

I just evacuated it again. I'll add the refrigerant and just check the gauges and check for leaks now that I have the dye in the system.

Shepherd777 on Wed November 16, 2011 11:21 AM User is offlineView users profile

Okay I added one can of freon and the dye. It appears that the high side inlet into the compressor is leaking. It has a new O-Ring. I was going to clean up the mating seats with emery cloth and re-oil the O-Ring and re-install.

The lower leak is by that sensor. I don't even know what that does, but I do not need it in my application. It is a new Sanden compressor. I removed the little metal bracket that holds on the sensor and gently pulled the wires, but it does not budge.

Does anyone know how it is removed or how I can plug up that sensor port???

The compressor has not run yet. Would that port sensor port seal just expand and seal itself up once the compressor pumps refrigerant and oil through the system?


Edited: Tue November 22, 2011 at 12:03 PM by Shepherd777

JACK ADAMS on Wed November 16, 2011 12:42 PM User is offline

The switch is a heat switch that only picks up heat off the case and may not have an open port behind it. So spillage may be the cause there. As for the fitting ports, did the compressor have oil in it? May have popped oil out when you pulled the caps off the case of the compressor. Don’t know really what to say but fill the system with some Nitrogen and do a soapy bubble test at those points. Don’t run the system thou with the nitrogen. We use Big Blu in our shop. Hope this helps..

Shepherd777 on Wed November 16, 2011 5:29 PM User is offlineView users profile

Hi Jack -

Thanks for the reply.

The compressor has oil in it. I added about 1/3 ounce of dye to that high side line when I had it off. I originally thought some just spilled on the compressor case when I reinstalled that line. But yesterday before I went home, I cleaned that top high side port area, and the heat switch area. When I installed it, I had 60#of system pressure. After a few hours it was down to 30# remaining in the system from that one can. When I returned this morning, I had 10# of pressure and both compressor areas were marked with dye again. I don't want to try and find a small bottle of nitrogen at this time.

Won't 60# of pressure from a new can of freon do the same thing as the nitrogen?

mk378 on Wed November 16, 2011 6:45 PM User is offline

You can pressure test with refrigerant if that's all you have. You could also use argon, CO2, MIG welder gas, etc. anything that is clean dry and inert -- NOT oxygen or acetylene! Since it leaks at 10 psi you don't need more than that for the test.

It sounds like it might be the wrong o-ring to make the seal, too small a cross section.

ice-n-tropics on Fri November 18, 2011 2:49 PM User is offline

My 2 cents:
Freightliner did use a Visteon controlled capacity scroll comp for a short time, but that scroll comp looks similar to a little tiny Honda civic comp which turns CCW. Ask bohica about the Ford Visteon scroll
The TPS (Thermal Protector Switch) does not have open communication with the refrigerant. There is a 4 mm thick aluminum wall beneath the TPS that eliminates refrigerant leakage. The TPS is fixed in place by special thermal RTV.
This KW truck A/C engineer would save his face by replacing that scroll with a TRSA120 Chevy Trailblazer scroll or better yet, a SD7H15 piston model.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Fri November 18, 2011 at 3:00 PM by ice-n-tropics

JACK ADAMS on Fri November 18, 2011 3:39 PM User is offline

I did notice that the fittings have been Tig welded, is this factory hose or rebuilt? If rebuilt it could have warped the pad mounting surface area with the heat. Either way will have to do a bubble test to pin point the leak. Just another thought !

Shepherd777 on Tue November 22, 2011 12:02 PM User is offlineView users profile

Gentlemen thanks for the replies. I've been working on other aspects of the project. Now back to the A/C.

Jack your hypothesis was correct.

We TIG welded those fittings. The system is obviously leaking there, although not as much as the pic would indicate. After one 12oz. can, pressure was 50# low & high. Now, 24 hours later it is only down to 15#. I added one can of freon and ran the compressor for a minute or two. Everything else seems okay except for those compressor fittings.

How do I proceed? Would removing the fittings from the compressor and filing the pad mounting surface flat work?

Or, do you or anyone else sell a non-split manifold that would bolt to this compressor?

We used previously-used hoses, cut off the mounting pads and welded those tubes to them. I thought the O-Rings would seal inside the compressor port and not between the two surfaces.

Edited: Tue November 22, 2011 at 12:06 PM by Shepherd777

JACK ADAMS on Tue November 22, 2011 2:25 PM User is offline

Since this is an aftermarket set up for this Kenworth (Not Factory) you will need to either try thicker O-rings or build new hoses and weld then not so close to the pad surface. Filing the surface will only add to your problem, not fix it! Good luck and let us know.

Shepherd777 on Tue November 22, 2011 6:03 PM User is offlineView users profile

Thanks, again Jack. I'll take the hoses off tomorrow and check it out.

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