Jump to content

Server Lease Renewal/Software Licenses

Our yearly server lease, software licenses, as well as hardware operating costs, ARE due Dec 6th, 2021. Our current donations have fallen far short of the funds we need to renew. Please remember the RennTech.org community is Member supported so please consider a donation to help...  THANK YOU!

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

Porsche early A/C design tutorial...or NOT.


wwest

Recommended Posts

In my opinion the early 911 A/C system design parallels the one in my MH, or even a typical window A/C.

The only control point is the temperature of the evaporator vane surfaces or the airflow through those surfaces. So what happens if that control point fails in a manner wherein the compressor runs continuously...?

In my MH or the typical window A/C the house circuit breaker might open, or is more typical the CB inside the compressor drive motor opens due to heating of the windings. Now the CB cycles every 5-7 minutes until the refrigerant pressure declines to the point that the motor will restart without tripping the CB.

So, what happens when the control system in these early Porsche A/C fail in the same manner, how did the Porsche factory design prevent subsequence damage to the compressor due to "slugging", liquid refrigerant reaching, entering the compressor inlet. Or did they just ignore the issue..?

Is the clutch designed to begin slipping with too much refrigerant pressure? Is the compressor itself of somehow a design that limits downstream pressure? A spring loaded relief valve, Pressure CB, that ports downstream pressure back into the inlet if pressure rises too high...? Or is the factory recommended refrigerant charge intentionally low enough that the compressor running continuously will not, will NEVER result in slugging?

My advice to anyone is that BEFORE you begin upgrading your factory A/C you should either find a positive answer to one of the above questions or add a hi/lo pressure switch downstream of the compressor so the (old/ new) compressor doesn't inadvertently destroy itself.

Link to comment
Share on other sites

The A/C compressor will turn off if the freon pressure is below a set point with an electrical switch located in the low pressure side of the system or through a mechanical switch that monitors if the evaporator freezes up. There is also a fuse for the clutch electrical circuit to prevent overloading and a mechanical pressure blow off valve on the high side circuit.

Link to comment
Share on other sites

The A/C compressor will turn off if the freon pressure is below a set point with an electrical switch located in the low pressure side of the system or through a mechanical switch that monitors if the evaporator freezes up. There is also a fuse for the clutch electrical circuit to prevent overloading and a mechanical pressure blow off valve on the high side circuit.

The only control point I can find, discern, on my '88 Carrera is the capillary thermostatic switch that is used to control the temperature setpoint of the evaporator/evaporator airflow. If the capillary tube/bulb is not installed correctly, buried, within the evaporator cooling vane area the evaporator could freeze up and that would result in a failed compressor due to slugging. Since the thermostatic switch seems to be so highly prone failure, failure in a way that results in the compressor running continuously, what provisions, if any, did Porsche make to prevent this type of escalating failure...?

Link to comment
Share on other sites

If the evaporator freezes up and the control switch is working/installed correctly it will interrupt current to the compressor clutch.

Or...

The evaporator will NOT freeze up if the control switch is working/installed correctly because it will interrupt the current to the compressor clutch before, ~35F, the evaporator cooling vanes reach a freezing temperature..

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.