Perth-WRX.com  

Go Back   Perth-WRX.com > Technical > Mechanicals
Register Diddy Kart ArticlesAll AlbumsBlogs FAQ Members List Calendar Search Today's Posts Mark Forums Read


Welcome to Perth-WRX, click here to register!

Reply
 
LinkBack Thread Tools Display Modes
  #11  
Old 06-02-2010, 01:26 AM
Rossco's Avatar
Perth WRX Old Skool Cool Dude
Member
 
Join Date: Apr 2007
Location: Perf, NOR
Posts: 5,467
Blog Entries: 11
Thanks: 54
Thanked 100 Times in 79 Posts
Rossco is a guruRossco is a guru
Send a message via MSN to Rossco
Default

No offense taken, a house is a completely different scenario though.

Houses generally don't exceed 60+ degrees inside unless they're on fire.

Let's compare some interesting numbers..... (sorry op)

Average automotive Hvac system:

20,000 Btu/hr (average)
Outside (fresh) air, Panel Vents
30 deg c Ambient + radiant heat absorbtion
50% relative humidity
= outlet temp 2-3 deg C

Note that the 20,000 BTU/hr works out to just less than 8 hp delivered (do the math), and assuming a reasonable compressor efficiency, this puts you back to the 10-15 kw region for draw from the compressor, not including the additional electrical (alternator) load added by the evap fan (100w), condenser fans (175w each) and the a/c clutch itself (50w).

Compared to a house a/c where a 12000-Btu/hr air conditioner is usually sufficient for approximately 550 to 650 sq. ft.

This is not too surprising really if you think about it for a second, it doesn't take long to pull down a 60 deg C car interior to something more reasonable.

/Infomercial

back on topic

If the comp is failing the belt will start to scream/slip as the load goes through the roof.

check the tensioner pulley bearing also, it's only under real load when the a/c clutch is engaged.

Look around the engine bay for belt dust near the a/c belt's path.
__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]

Last edited by Rossco; 06-02-2010 at 01:29 AM.
Reply With Quote
  #12  
Old 08-02-2010, 09:51 AM
DCCD Donut Driver
Member
 
Join Date: Feb 2010
Location: perth
Posts: 79
Thanks: 0
Thanked 0 Times in 0 Posts
blurex at standard level
Default

your calculations do make a some sense but i honestly dont know exactly many Kw's you would need to cool the volume of air inside a standard house (over a given period of time), but isnt it safe to assume you need considerably lower Kw's to cool the volume in a car?.. however you may be right about the bearing, the vibration/ rattle "feels" like its coming from a moving/or rotating component, I'll check for belt dust as you suggested, and post what i find ...please any more suggestions on what could be wrong.. Cheers guys
__________________
Aint no stupid like right-wing stupid.....
Reply With Quote
  #13  
Old 08-02-2010, 10:08 AM
Rossco's Avatar
Perth WRX Old Skool Cool Dude
Member
 
Join Date: Apr 2007
Location: Perf, NOR
Posts: 5,467
Blog Entries: 11
Thanks: 54
Thanked 100 Times in 79 Posts
Rossco is a guruRossco is a guru
Send a message via MSN to Rossco
Default

It's all to do with heat absorbtion of the cars structure / interior materials.

Trying to cool an uninsulated tin shed the size of your house would take 3-4 times more cooling than a modern double brick, insulated house needs.

[a/c 101]

Is your car performing any better in the current milder weather?
__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]
Reply With Quote
  #14  
Old 08-02-2010, 10:36 AM
DCCD Donut Driver
Member
 
Join Date: Feb 2010
Location: perth
Posts: 79
Thanks: 0
Thanked 0 Times in 0 Posts
blurex at standard level
Default

The car's performance DOES vary with changes in weather as would be expected, even when the a/c if off ( which supports your earlier assumption of the Pod aiding in sucking in more hot/ cool under bonnet air)...Am struggling to come to terms with the fact that the vibration can only be caused by a worn out component or loose fitting (due to wear), and from what you guys say its either a 1. worn clutch, 2. loose/worn belt, 3. Worn bearing..am hoping the problem ends there as fixing an a/c can be quite costly.. I'll check for any other fault signs and let you know...do you know of any good a/c specialists (not necessarily subaru ones)... cheers
__________________
Aint no stupid like right-wing stupid.....
Reply With Quote
  #15  
Old 08-02-2010, 07:14 PM
WhiteRX's Avatar
Subaru Tech Division
Member
 
Join Date: Jul 2005
Location: Perth
Posts: 1,252
Thanks: 2
Thanked 3 Times in 3 Posts
WhiteRX at standard level
Send a message via MSN to WhiteRX
Default

Temperature is irrelivent, as the compressor doesnt use any more power if the air it is cooling is hotter.

Now your average 6pk drive belt tensioned correctly can achive about 14kw power transmission. a 3pk belt can achive up to about 3kw of power transmission. The subaru ac comp uses a 4pk drive belt, which can handle a max of 5kw power transmission before slipping.
Something that mechanics are taught at tafe. I take it that you arent a mechanic?

Now even more so. When i did my airconditioning training we set up a compressor on a test bench, with a cars evaporator, which was run by a 1.5hp motor. It achived normal gas pressures and cooled to the same standards as a car aircon, infact it was the same thing on a test bench.

The aircon compressor clutch is a magnetic clutch, which has too friction discs that are about 10mm wide, by 70mm dia. that drives a shaft which is about 8mm diameter. This shaft defiantly couldnt handle 15kw.

seriously how much power do you think a compressor can use?


Quote:
Originally Posted by Rossco View Post
No offense taken, a house is a completely different scenario though.

Houses generally don't exceed 60+ degrees inside unless they're on fire.

Let's compare some interesting numbers..... (sorry op)

Average automotive Hvac system:

20,000 Btu/hr (average)
Outside (fresh) air, Panel Vents
30 deg c Ambient + radiant heat absorbtion
50% relative humidity
= outlet temp 2-3 deg C

Note that the 20,000 BTU/hr works out to just less than 8 hp delivered (do the math), and assuming a reasonable compressor efficiency, this puts you back to the 10-15 kw region for draw from the compressor, not including the additional electrical (alternator) load added by the evap fan (100w), condenser fans (175w each) and the a/c clutch itself (50w).

Compared to a house a/c where a 12000-Btu/hr air conditioner is usually sufficient for approximately 550 to 650 sq. ft.

This is not too surprising really if you think about it for a second, it doesn't take long to pull down a 60 deg C car interior to something more reasonable.

/Infomercial

back on topic

If the comp is failing the belt will start to scream/slip as the load goes through the roof.

check the tensioner pulley bearing also, it's only under real load when the a/c clutch is engaged.

Look around the engine bay for belt dust near the a/c belt's path.
__________________
Version 6 STI
Reply With Quote
  #16  
Old 08-02-2010, 09:58 PM
Rossco's Avatar
Perth WRX Old Skool Cool Dude
Member
 
Join Date: Apr 2007
Location: Perf, NOR
Posts: 5,467
Blog Entries: 11
Thanks: 54
Thanked 100 Times in 79 Posts
Rossco is a guruRossco is a guru
Send a message via MSN to Rossco
Default

You are correct (and I never said) "the compressor uses more power to cool hotter air".......The system does how ever need to be sized to take into account it's working environment and performance expectations (pulling the cars interior down from 60+ degrees to around 20 deg or less and maintain it).

Ambient temperature absolutely plays a part in automotive a/c..... A condenser doesn't reject heat at a constant rate regardless of ambient temperature and / or airflow, does it?........It's basic physics.

Your trying to tell me that your bench demo a/c was a 20,000 btu set up running on 1.5 hp?.......Sorry, but I don't think so.

Do you honestly think a 1.5 hp system will cool your car on a 35 degree day?

The rated belt loadings you mention are interesting, seeing as the commode super charger / auxiliary drive belt (8pk) on the supercharged v6 delivers 30-40 kw to drive the factory eaton supercharger when it's producing only 8-9 psi (and up to 70kw when the supercharger is overdriven to produce 10 - 12 psi).........Plus the same single belt also drives the a/c, water pump, power steering & alternator.

Me a mechanic?......I can't even change oil.....

In regard to BTU = watts
20,000 BTU per hour = 5.858 Kw (7.855 Hp) @ an unrealistic 100% efficiency.
__________________
[CENTER][SIGPIC][/SIGPIC][/CENTER]
[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]
Reply With Quote
Reply

Tags
air, con, problems

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Many Problems mitcho Mechanicals 19 05-02-2010 10:39 AM
cpu problems HELP q2cmy00 Non-WRX Discussion 14 23-01-2009 06:36 PM
Need help on 2 problems! Elrico Mechanicals 7 02-07-2007 05:02 PM
PC Problems...For the IT Superheros MRWATO2U Non-WRX Discussion 8 30-01-2007 01:20 PM
AFM Problems VSP3CB Mechanicals 2 31-01-2006 09:02 PM



Welcome to Perth-WRX, click here to register!

All times are GMT +8. The time now is 08:54 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO