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Mighty Meatlocker Turbo
 
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Join Date: Apr 2016
Location: North TexASS
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Quote:
Originally Posted by tsuter View Post
. . .
RPMs need to be over 2000 when charging to get the R134a charge correct. Won't get it right at idle.
. . .
That is absolutely not correct.
Old 07-21-2018, 07:16 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #41 (permalink)
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1) Do inspect the bottom of the evaporator core through the RH air inlet plenum; mirror and flashlight. Ask Discseven to read you the riot act.
2) Do inspect the air outlet tube at the evaporator box as well as the air tube/shroud connected the primary AC vent above the radio.
3) A normally functioning system: the inlet refrigerant hose fitting to the expansion valve will be warm to hot. The outlet refrigerant hose fitting on the evaporator outlet will sweating to frosty; cold. If your refrigerant line from the drier outlet up to the TEV is cold, then gas is expanding in the line rather than out the bottom of the TEV.
The line from the drier to the TEV needs to be warm to hot.
4) On a properly evacuated and properly charged R134a system, a low side pressure of 30 psi suggests and evaporator outlet temperature of approximately 35F nominal.
5) You cannot "adjust" the super heat spring load on a typical 911/930 expansion valve while it is attached to the evaporator. The adjustment allen nut is located inside its outlet section which attached to the evaporator's inlet tube. Don't screw with it, there is nothing of any great significance in performance to achieve; if you think you did achieve something it usually relates to a better evacuation after you played with in and put it back on.
6) Observations you can make of a TEV are either its working normally, the valve is clogged with debris (compressor parts, hose parts, descant from the drier or ice that formed internally because of a poor evacuation, or the valve failed because the refrigerant in its sensing capillary tube (copper pipe with the pigtail clamped on the evaporator outlet pipe) leaked out. The valve is stuck open. On a properly evacuated and fully charged system a normally functioning TEV showing the low side is 30 suggests the valve is open, less than 10 then the valve is nearly closed, much higher than 40 then the valve is open. If the system is not properly evacuated or not properly charged it becomes difficult state for sure that a valve is suspect. You need a properly evacuated and properly charged (known amount of refrigerant, accurate gauge readings) system to start off with.
7) The 911/930 is not a small system.
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Kuehl
1987 911 cab, modified
https://griffiths.com/
Old 07-21-2018, 08:00 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #42 (permalink)
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Location: San Antonio, Texas
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Quote:
Originally Posted by Rawknees'Turbo View Post
That is absolutely not correct.

It is ABSOLUTELY correct. Bold added for emphasis. Hahahaha!
At idle your compressor won't be spinning fast enough to achieve the necessary pressures for charging properly. Even with a nice Sanden rotary SD507 or even nicer SD5H14!
Unless you're charging by weight! Which most peeps are not.
Muhahahhahaha!
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tsuter
78 911SC Turbo Targa
Thaaaats Right!!
Old 07-21-2018, 10:44 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #43 (permalink)
Mighty Meatlocker Turbo
 
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Join Date: Apr 2016
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Quote:
Originally Posted by tsuter View Post
It is ABSOLUTELY correct. Bold added for emphasis. Hahahaha!
At idle your compressor won't be spinning fast enough to achieve the necessary pressures for charging properly. Even with a nice Sanden rotary SD507 or even nicer SD5H14!
Unless you're charging by weight! Which most peeps are not.
Muhahahhahaha!
It might be correct for you, but it is incorrect for me, pros such as Charlie Griffith (Kuehl), and countless other professionals and hobbyists that have been charging r134a by the vent temperature & pressures method for decades (whenever weight information is not available, a system has been customized, etc.). I have never once charged at any engine speed above idle, on any vehicle, and get ballfreezing results with perfect pressures for the given air temp in the garage, every time (baring some sort of problem, buttofcourse).

In other words, you are stating an opinion about, or preference for, a certain charging procedure, and presenting it as fact, when it clearly is not. And the whole "compressor not spinning fast enough at idle" is just plain wrong.

Last edited by Rawknees'Turbo; 07-21-2018 at 07:46 PM..
Old 07-21-2018, 07:41 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #44 (permalink)
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Not taking any sides of bets in the debate:

"RPMs need to be over 2000 when charging to get the R134a charge correct. Won't get it right at idle."

Well, the statement above could mean that when you are charging by vapor (can up) at "idle" and the pressure in the vehicle's system starts climb (as refrigerant enters the system) and equals the pressure in the refrigerant can, it is very difficult for the system to pull in more refrigerant. This is commonly experienced by DIY's on their first charging experience. However, by increasing the pressure of the refrigerant can, such as by placing the small 12 or 16 oz can in warm water, or by attaching an electric heating blanket around a 30lb refrigerant can, you can move refrigerant into the system quicker.
Or, you can increase the rpms of the engine with reduces the vehicles low side pressure as well increases the pumping cycles of the compressor per minute which assists in moving the refrigerant from the refrigerant can into the vehicle is less time.
We typically charge by liquid (through the high side, engine off) to a predetermined weight simply because it is quicker and finalize the charge using vapor (through the low side engine running). DIY's.... stick with the vapor method so you don't liquid slug a compressor on your first experience and smash the reeds.

The "2,000" rpm check suggested in some manuals simply happens to be a number some person at the factory picked for 'checking' the system. It is not the gold standard by any means. For example, when a vehicle is moving in slow traffic or sitting at stop light or in dead traffic, the biggest complaint is the air temps are not cold enough. Naturally this is because the air flow on the engine deck lid is reduced and the volume of refrigerant flowing through the system is reduced.
Our preference is to charge and test the system charge pressures at idle. You can do this if you know what the Pressures and Temperatures should be at idle.
I'm sure you could come with P&T's at any given rpm but I have not concluded it is simply linear.

With respect the broad range of high side pressures noted:
Ambient 70-80F = 115-200psi
Ambient 80-90F = 140-235psi
Ambient 90-100F = 165-270psi
Ambient 100-110F = 210-310psi

They are as vague as the 964/993 pressure and temperature ranges in the 964 and 993 manuals; and there is obviously a reason why they made them broad, because the factory, during this time frame, was better with engine performance specs, not AC systems.
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1987 911 cab, modified
https://griffiths.com/

Last edited by kuehl; 07-21-2018 at 08:48 PM..
Old 07-21-2018, 08:45 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #45 (permalink)
Original Owner
 
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Join Date: Dec 2002
Location: San Antonio, Texas
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Quote:
Originally Posted by Rawknees'Turbo View Post
It might be correct for you, but it is incorrect for me, pros such as Charlie Griffith (Kuehl), and countless other professionals and hobbyists that have been charging r134a by the vent temperature & pressures method for decades (whenever weight information is not available, a system has been customized, etc.). I have never once charged at any engine speed above idle, on any vehicle, and get ballfreezing results with perfect pressures for the given air temp in the garage, every time (baring some sort of problem, buttofcourse).

In other words, you are stating an opinion about, or preference for, a certain charging procedure, and presenting it as fact, when it clearly is not. And the whole "compressor not spinning fast enough at idle" is just plain wrong.
Hahahaha. Jim Sims RIP is rolling over in his grave now. Even Sadie Carnot would be impressed.

The Sanden isn't the compressor on your Daddy's GM Duramax 6.6 Liter V8 truck that idles at 550 rpm and is maxed at 3000 rpm.

The "search" is your friend....my friend ..... you who joined the forum yesterday! Or maybe a couple Porsche bulletins????

When you have 20,000 hits on one of your HVAC threads get back to me.

Muhahhaha!

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tsuter
78 911SC Turbo Targa
Thaaaats Right!!
Old 07-22-2018, 04:22 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #46 (permalink)
 
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Wow, this sounds a lot like the problem I've been fighting for couple years now...high pressures with what appears to be an undercharged system. I'm about to try and do some tasing on my TEV to see if maybe that's where the problem lies. I don't think I fully understand the reason for checking how soon the high and low side equalize after shut down. I know they will go to about 110 but I have never bothered to see how long this process takes.
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Last edited by 88911coupe; 07-23-2018 at 07:02 AM..
Old 07-23-2018, 05:53 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #47 (permalink)
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3) A normally functioning system: the inlet refrigerant hose fitting to the expansion valve will be warm to hot. The outlet refrigerant hose fitting on the evaporator outlet will sweating to frosty; cold. If your refrigerant line from the drier outlet up to the TEV is cold, then gas is expanding in the line rather than out the bottom of the TEV.
The line from the drier to the TEV needs to be warm to hot.


It does not require a laser or probe, put your fingers on the evap outlet hose fitting or or TEV inlet fitting.
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1987 911 cab, modified
https://griffiths.com/
Old 07-23-2018, 05:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #48 (permalink)
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