Re: [MBZ] 1982 300SD AC Question

[Mitch Haley via Mercedes]

> On August 15, 2016 at 11:25 PM Jim Cathey via Mercedes 
> wrote:
 
> Fill it, and rejoice.

Agreed. At least with R12 you can fill until the bubbles go away in the sight
window. 
120 psig is about 102 degrees F. If you were moving much heat to the condenser,
it would be higher I'm sure. 

7 psig is about -4F. You want to see close to 35psig. I thought the low pressure
switch killed the compressor at something like 20 or 30 psi.

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Re: [MBZ] 1982 300SD AC Question

[Jim Cathey via Mercedes]

>
> went to 120 high side and 7 low side.  So my R12 is quite low


Yes.  Ignore the pressures for the moment, and look at the _temperature_
scale on the gauges.  Your high-side temperature would be what?  Just how
much heat do you think you're able to take out of the 'hot' side at that
temperature
differential (with the air)?  If you can't suck the heat out there, then
there's
no place for it to move heat out of the cabin into, and the whole thing
nearly
flatlines.

On the low side, the thing is damned near sucking a vacuum.  How much
flow do you think you'll be getting then?  You are dangerously near the
point
where lubricating oil is not flowing.  (Presumably your low-pressure cutoff
would kick in before that point, though.)

AC systems are deceptively simple, but there's a lot of basic physics going
on,
in a system that is designed and optimized for one operating point.  Miss
that
point, and it all goes to hell.

Fill it, and rejoice.

-- Jim
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Re: [MBZ] 1982 300SD AC Question

[Kaleb C. Striplin via Mercedes]

You have a low charge

Sent from my iPhone

> On Aug 15, 2016, at 9:42 PM, Scott Ritchey via Mercedes 
>  wrote:
> 
> I put gauges on it today.  Pressures were 72 hot side and 79 cold side
> before engine start.  I attribute the difference to my cheap, old gauges
> (pre Harbor Freight gauges from JC Whitney).  After engine start pressures
> went to 120 high side and 7 low side.  So my R12 is quite low but would that
> account for the apparent lack of flow?  After engine shutdown, pressure
> blead to 105/75 within about 30 sec but was still 90/78 after about 5
> minutes.
> 
> The big difference (120 high side 7 low side) and slow bleed-down make me
> think the compressor is doing its job but refrigerant is low and not getting
> past the dryer or expansion valve.  Maybe that's normal for such low R12
> levels.  I need to research that expansion valve to see if this (no flow) is
> normal for such conditions.
> 
> Thanks for insights.  Scott
> 
>> -Original Message-
>> From: Mitch Haley via Mercedes
>> Sent: Sunday, August 14, 2016 12:37 PM
>> 
>> If you have gauges you can at least find out if it's very  low on charge
> or if
>> there's something mechanically wrong.
>> 
>> Or you can throw in 12oz of R12 and see what happens. It's common for old
>> cars to leak.
>> 
>> Mitch.
> 
> 
> 
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Re: [MBZ] 1982 300SD AC Question

[Scott Ritchey via Mercedes]

I put gauges on it today.  Pressures were 72 hot side and 79 cold side
before engine start.  I attribute the difference to my cheap, old gauges
(pre Harbor Freight gauges from JC Whitney).  After engine start pressures
went to 120 high side and 7 low side.  So my R12 is quite low but would that
account for the apparent lack of flow?  After engine shutdown, pressure
blead to 105/75 within about 30 sec but was still 90/78 after about 5
minutes.

The big difference (120 high side 7 low side) and slow bleed-down make me
think the compressor is doing its job but refrigerant is low and not getting
past the dryer or expansion valve.  Maybe that's normal for such low R12
levels.  I need to research that expansion valve to see if this (no flow) is
normal for such conditions.

Thanks for insights.  Scott

> -Original Message-
> From: Mitch Haley via Mercedes
> Sent: Sunday, August 14, 2016 12:37 PM
> 
> If you have gauges you can at least find out if it's very  low on charge
or if
> there's something mechanically wrong.
> 
> Or you can throw in 12oz of R12 and see what happens. It's common for old
> cars to leak.
> 
> Mitch.



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Re: [MBZ] 1982 300SD AC Question

[Mitch Haley via Mercedes]

If you have gauges you can at least find out if it's very  low on charge or if
there's something mechanically wrong. 

Or you can throw in 12oz of R12 and see what happens. It's common for old cars
to leak. 

Mitch.

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Re: [MBZ] 1982 300SD AC Question

[Scott Ritchey via Mercedes]

I should have been more clear.  The line from the compressor to the AC
radiator was hot; hotter than I could touch continuously.  The top few tubes
in the radiator were warm.  Everything else was ambient.  I'm thinking about
pulling the under-dash panel and giving the TXV a few taps (in case it is
stuck).  The car is still 100% R12 and I don't have a recovery system so
I'll probably need to go to a pro for any repair that involves replacing
parts.

> -Original Message-
> From: Mercedes [mailto:mercedes-boun...@okiebenz.com] On Behalf Of Mitch
> Haley via Mercedes
> Sent: Sunday, August 14, 2016 9:28 AM
> To: Mercedes Discussion List <mercedes@okiebenz.com>
> Cc: Mitch Haley <mi...@mitchellhaley.com>
> Subject: Re: [MBZ] 1982 300SD AC Question
> 
> Ambient could mean no or little flow,
> cold (refrigerated) means pressure drop and boiling refrigerant.
> 
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Re: [MBZ] 1982 300SD AC Question

[Mitch Haley via Mercedes]

Ambient could mean no or little flow, 
cold (refrigerated) means pressure drop and boiling refrigerant.

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Re: [MBZ] 1982 300SD AC Question

[Scott Ritchey via Mercedes]

Thanks.  I'll try the gauges (it was getting dark so I had to quit last 
evening).  I had the impression that there was no flow through the system.  
Maybe the dryer is plugged?  As I recall, the dryer was normally quite warm 
during normal operation nut it was cold (ambient).  For Mitch, I saw no damage 
to the radiator.

> -Original Message-
> From: Mercedes [mailto:mercedes-boun...@okiebenz.com] On Behalf Of Jon
> Agne via Mercedes
> Sent: Sunday, August 14, 2016 8:11 AM
> To: Mercedes Discussion List <mercedes@okiebenz.com>
> Cc: Jon Agne <jonag...@gwi.net>o
> Subject: Re: [MBZ] 1982 300SD AC Question
> 
> You really cannot tell by feel what’s going on in the AC system without
> hooking up the gauges.  Could be low refrigerant.
> 
> 
> > On Aug 14, 2016, at 12:04 AM, Scott Ritchey via Mercedes
> <mercedes@okiebenz.com> wrote:
> >
> > I noticed the AC on my 300SD wasn't cooling today.  This car had not
> > been run for months.  The line from the compressor to the radiator was
> > quite hot but the top of the AC radiator was barely warm.  The bottom
> > of the radiator was cold and the receiver-dryer (and everything
> downstream) was cold.
> >
> > For those with more hands-on experience:  Is this likely a stuck
> > expansion valve?  A plugged AC radiator?
> >
> > Scott
> >
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> 
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Re: [MBZ] 1982 300SD AC Question

[Mitch Haley via Mercedes]

Drops in temperature occur where there are drops in pressure. 

If it happens where there's no intended orifice/expansion valve, there's
probably something restricting flow at that point. Is this a serial flow
condenser, and did something hit the condenser pinching the tube flat where the
temperature drops?

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Re: [MBZ] 1982 300SD AC Question

[Jon Agne via Mercedes]

You really cannot tell by feel what’s going on in the AC system without hooking 
up the gauges.  Could be low refrigerant.


> On Aug 14, 2016, at 12:04 AM, Scott Ritchey via Mercedes 
>  wrote:
> 
> I noticed the AC on my 300SD wasn't cooling today.  This car had not been
> run for months.  The line from the compressor to the radiator was quite hot
> but the top of the AC radiator was barely warm.  The bottom of the radiator
> was cold and the receiver-dryer (and everything downstream) was cold.  
> 
> For those with more hands-on experience:  Is this likely a stuck expansion
> valve?  A plugged AC radiator?
> 
> Scott
> 
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