| Author |
Message |
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
 Posted: Sat Jul 22, 2017 6:34 am Post subject: Delta T standard for A/C? |
 |
|
I know in home HVAC you measure the delta t of the system to see if it's working up to it's potential.
delta T is the temp of the air going in minus the temp if the air coming out.
is there one for the van?
I know people say ~40° at the vents, but what is the tested ambient temp and conditions?
Im trying to figure out if my completely new system is running up to par.
it was only "comfortable" in the van yesterday in my real-world trial on high but then
I realized it was a very humid, 99°, full sun, and in traffic.
driving home last night it was 88°, still humid, but open road and it frosted me out on low.
I feel a delta T standard would be more valuable. but what do I know.
thoughts?
ps. on a side note, I found that in my early-style westy AC,
if you remove the whole AC vent cover it's like a whole new world of air flow up front.
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
 |
Abscate
Samba Member
Joined: October 05, 2014
Posts: 22665
Location: NYC/Upstate/ROW
|
| Posted: Sat Jul 22, 2017 7:02 am Post subject: Re: Delta T standard for AC? |
|
|
Delta T is good because it measures heat carrying capacity, which is independent of temperature, to a good approximation. . Until you hit freezing of pipes , you will get the same temp delta in the NE and the desert, watching for sun load of course.
Humans suck at evaluating performance by comfort level. An 80 degree F car in 105F ambient will feel great!
I don't know Bay specifics but a rough guide on my fleet is
30F service required
35F ok
40F good
45F don't touch anything!!
I'm a complete wimp in the heat, im guessing most can live with a 30F delta
Pet peeve.. "topping up every year." Fix your damn Freon leak so
You don't torch the planet, or live without AC.
_________________
.ssS! |
|
| Back to top |
|
|
skills@eurocarsplus
Samba Peckerhead
Joined: January 01, 2007
Posts: 16878
Location: sticksville, ct.
|
| Posted: Sat Jul 22, 2017 11:03 am Post subject: Re: Delta T standard for AC? |
|
|
if your evaporator froze up you have pressure problems. well usually....you could have a low charge, poor flow thru the evap or the system is over filled with oil, and flooding the evaporator.
another thing I have seen cause evap freeze up is poor drainage. you need to get the sweat off of the evaporator.
also, HIGH fan speed reduce efficiency....this is why for maximum cooling all a/c is set at mid speed and measured at the center vent @2K rpm's
_________________
| gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
| Jake Raby wrote: |
| Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
| Brian wrote: |
| Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
|
|
| Back to top |
|
|
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
| Posted: Sat Jul 22, 2017 7:59 pm Post subject: Re: Delta T standard for AC? |
|
|
thanks guys for the replies.
she's definitely NOT freezing up. 
doing more testing today and am getting some odd readings.
at 1500rpm Im 40 low side and 220 high side.
vent temps have never been below 60 that Ive seen.
I starting to think I may have a bad expansion valve.
Unfortunately I used a cheapy I had bought a while back before I decided to redo the whole system from scratch.
ordered a good one today…
we will see. 
Why do it once when you can do it twice!™
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
|
Farf
Samba Member
Joined: July 12, 2009
Posts: 463
Location: Colorado
|
| Posted: Sat Jul 22, 2017 8:59 pm Post subject: Re: Delta T standard for AC? |
|
|
| slackin' at work wrote: |
| ...driving home last night it was 88°, still humid, but open road and it frosted me out on low. |
| slackin' at work wrote: |
| ...vent temps have never been below 60 that Ive seen. |
A little bit confused by your statements above. Are you having problems only when testing in the driveway? Condenser fan is running? Have you provided additional cooling (box fan or water mist) to the condenser? What refrigerant are you using? |
|
| Back to top |
|
|
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
| Posted: Sat Jul 22, 2017 9:35 pm Post subject: Re: Delta T standard for AC? |
|
|
yeah I know. a little confusing.
I didn't have my thermometer up there on that said evening drive.
so I have no idea how chilly it was. I do know it was cooler then during the day.
I took the reading this morning before the radiator/condenser would have
gotten heat-sink. the rad fan does run as supposed to when the ac is on.
Im running red tek (3cans). I had great luck in the old system when running my wbx.
but now Im running a subaru so finally got to all hooked up. compressor is a new refurb.
new 16x22 cross flow condenser. new everything actually, aside from the evaporator.
I feel this baby should be down right cold out the vents. the weakest link, to me, would be the expansion valve but willing to hear other ideas.
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
|
djkeev
Samba Moderator
Joined: September 30, 2007
Posts: 32625
Location: Reading Pennsylvania
|
| Posted: Sun Jul 23, 2017 5:10 am Post subject: Re: Delta T standard for AC? |
|
|
I rebuilt my A/C system completely.
I ignored the experienced warnings from TerryK about new expansion valves often not working in these large systems and put in a new one.
BIG MISTAKE!!!
I took off for Oregon in late August and had only marginal A/C then had essentially zero cooling by Ohio.
We suffered through 97* in North Dakota stopping in Fargo to buy a HF vacuum pump.
I had my house sitter locate and mail my original old expansion Valve to my daughter in Great Falls Montana. (I had brought my gauges and extra RedTek "just in case" )
I drained the system, put in the old Valve and Viola' !!!! We froze our butts off to Oregon!
I Just used the system last weekend in severe three H weather..... my Wife put on a sweat shirt while I and Grover (an always hot Golden) enjoyed the cold air!!
I talked to Terry about the new valves not working. He thinks it is the preset adjustment of them. There is an internal adjustment screw but because of the work involved to experiment with one, I haven't done any tinkering.
If my system didn't work and my old valve was dead, I'd for sure try adjusting one.
Dave
_________________
Stop Dead Photo Links how to post photos
Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473
Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537
Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert |
|
| Back to top |
|
|
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
| Posted: Sun Jul 23, 2017 5:51 am Post subject: Re: Delta T standard for AC? |
|
|
Dave, I remember you having issues with your valve. I didn't remember
the story of you putting on your old one… or the cross-country fiasco to
get it out to you.
I just ordered a german Behr unit from BD. so hoping for some
appropriate settings.
oddly the valve I did get (Global part# 3411265) also lists compatible
with a 80s honda. red flag #1 perhaps.
I may actually still have my original one somewhere in the workshop. hmm.
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
|
JudoJeff
Samba Member
Joined: May 24, 2013
Posts: 1179
Location: Near Springfield, MA
|
| Posted: Sun Jul 23, 2017 6:09 am Post subject: Re: Delta T standard for AC? |
|
|
I expect a Delta T of 40-50 degrees. However, with a blended refrigerant, your glide affects how the system works. A single refrigerant will perform exactly to it's printed T/P chart. Blends evaporate the high boiler first, then the lower, etc. So the system performs at different ranges. If your TXV is setup for the single, supercool and superhot may not occur. So tweaking of the controls is necessary.
_________________
________________________________________
1989 Vanagon GL Westfalia Camper, Burned up on 7/31/16.
1987 Vanagon GL Westfalia Camper, Bostig & Rebuilt, sold
1986 Vanagon GL Westfalia Camper, Bostig Sold May 10, 2021
1999 Ford GTRV Westfalia camper (30% bigger Westy layout) |
|
| Back to top |
|
|
djkeev
Samba Moderator
Joined: September 30, 2007
Posts: 32625
Location: Reading Pennsylvania
|
|
| Back to top |
|
|
Butcher
Samba Member
Joined: December 05, 2015
Posts: 1285
Location: Right Here
|
| Posted: Sun Jul 23, 2017 7:55 am Post subject: Re: Delta T standard for AC? |
|
|
Tweaking the valve is just adjusting the low pressure side. In a nut shell, anything less than 32psi will be too low and the evaporator will freeze up. If you look inside the valve, you will see some type of screw to move. When I went to school about this years ago, the low side pressure should be close to the temperature out of the vent.
The issue with adjusting the pressure is that you really do not know what it is unless the system is working. So hook it up, fill the system, check the pressures, evacuate, remove, adjust, etc. It can be expensive if you cannot recover the refrigerant. I would not adjust it lower than 34psi.
Each refrigerant it slightly different with the low pressure, but they are all close. |
|
| Back to top |
|
|
skills@eurocarsplus
Samba Peckerhead
Joined: January 01, 2007
Posts: 16878
Location: sticksville, ct.
|
| Posted: Sun Jul 23, 2017 9:03 am Post subject: Re: Delta T standard for AC? |
|
|
| Butcher wrote: |
I would not adjust it lower than 34psi.
|
agreed, but typically anything lower than 25psi on the low side will result in evaporator freeze up.
I just rebuilt the a/c in my 82 rabbit...every last bit of it is new...everything. I see about 39* out of the center vent at highway speeds, and about 43* around town. I wish I squeaked a bit bigger condenser in there, but whatever...cold air pours out of the vents.
_________________
| gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
| Jake Raby wrote: |
| Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
| Brian wrote: |
| Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
|
|
| Back to top |
|
|
Farf
Samba Member
Joined: July 12, 2009
Posts: 463
Location: Colorado
|
| Posted: Sun Jul 23, 2017 11:50 am Post subject: Re: Delta T standard for AC? |
|
|
Since you installed all new components in your van did you possibly pipe in your condenser (see attached photo link) with the liquid line on top? Doing this would give you the higher head and suction pressures that you have and better cooling at speed. Easy enough to take a look.
http://colorado4wheel.com/images/van/ac_install/IMG_6757.JPG |
|
| Back to top |
|
|
skills@eurocarsplus
Samba Peckerhead
Joined: January 01, 2007
Posts: 16878
Location: sticksville, ct.
|
| Posted: Sun Jul 23, 2017 12:40 pm Post subject: Re: Delta T standard for AC? |
|
|
just for clarification, that photo shows the wrong way to do it.
page 5 here shows a good layout
http://www.vintageair.com/AC%20Basics/AC%20Basics%204.23.15.pdf
_________________
| gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
| Jake Raby wrote: |
| Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
| Brian wrote: |
| Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
|
|
| Back to top |
|
|
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
| Posted: Sun Jul 23, 2017 2:02 pm Post subject: Re: Delta T standard for AC? |
|
|
an interesting thought. but I do have it run correctly.
I have an early van so the dryer is in the wheel wheel.
its run like the diagram on vintage air.
taped my thermometer in the vent this morning when driving
to the hardware store. thought for sure it would be low since it felt really nice.
nope… 58° 
I did test the thermometer in my daily driver and it seemed calibrated correctly.
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
|
Abscate
Samba Member
Joined: October 05, 2014
Posts: 22665
Location: NYC/Upstate/ROW
|
| Posted: Sun Jul 23, 2017 5:36 pm Post subject: Re: Delta T standard for AC? |
|
|
| slackin' at work wrote: |
an interesting thought. but I do have it run correctly.
I have an early van so the dryer is in the wheel wheel.
its run like the diagram on vintage air.
taped my thermometer in the vent this morning when driving
to the hardware store. thought for sure it would be low since it felt really nice.
nope… 58°
I did test the thermometer in my daily driver and it seemed calibrated correctly. |
If it was 90 out that's 32 degrees of delta, which isn't bad for a giant box
_________________
.ssS! |
|
| Back to top |
|
|
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
| Posted: Sun Jul 23, 2017 8:27 pm Post subject: Re: Delta T standard for AC? |
|
|
| Abscate wrote: |
| If it was 90 out that's 32 degrees of delta, which isn't bad for a giant box |
no. was 81 and overcast. 
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
|
JudoJeff
Samba Member
Joined: May 24, 2013
Posts: 1179
Location: Near Springfield, MA
|
| Posted: Mon Jul 24, 2017 6:30 am Post subject: Re: Delta T standard for A/C? |
|
|
Talking about blends again: where the bulb is placed in the evaporator fins makes a difference due to the glide. Under R12, it would have been closer to the expansion valve, using a blend, you have to move it farther away. Trial and error method to see what's best spot.
_________________
________________________________________
1989 Vanagon GL Westfalia Camper, Burned up on 7/31/16.
1987 Vanagon GL Westfalia Camper, Bostig & Rebuilt, sold
1986 Vanagon GL Westfalia Camper, Bostig Sold May 10, 2021
1999 Ford GTRV Westfalia camper (30% bigger Westy layout) |
|
| Back to top |
|
|
djkeev
Samba Moderator
Joined: September 30, 2007
Posts: 32625
Location: Reading Pennsylvania
|
|
| Back to top |
|
|
slackin' at work
Samba Member
Joined: May 07, 2003
Posts: 443
Location: Central Virginia
|
| Posted: Mon Jul 24, 2017 6:58 am Post subject: Re: Delta T standard for A/C? |
|
|
thanks again guys for keeping this thread going. it's given me plenty to think about.
the expansion valve bulb on mine is clipped onto the evaporator exit line.
right before it goes to rubber. then the whole thing is covered in cork tape.
which will be fun to take off again.
_________________
`20 SQ5
`06 Z4M coupe
`04 R32
`84 MK1 GTI
`76 Brasilia |
|
| Back to top |
|
|
|
