Question of cooling system design theory,I-5 engine

[Scott Phillips]

Tony, 

 

I understand the problem, and while I don't have any data to support an
answer, why not just extend you're original thought a bit and create a
simple valve-d bypass of the heater core using three valves:  

 

HC-i                                  HC-o

  |                                        |

Valve                             valve

|                                         |

  ______Valve______

|                                          |

Connection                    Connection

 

This way you retain the coolant flow, just are bypassing the "hot" into
the cabin..                   

 

 

Good Luck!

 

Scott

 

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com]
On Behalf Of Tony Hoffman
Sent: Tuesday, April 12, 2011 1:02 PM
To: quattro at audifans.com
Subject: Question of cooling system design theory,I-5 engine

 

Fellow Q-heads,

 

I have a question of theory as I'm working on the A/C system of my '86
4000 Quattro.

 

Firts, a little background. I live in Houston, where we already are
seeing

90 degree highs :( So, since my A/C compressor dies at the end of last
summer, I've decided to upgrade while I'm in there. I have installed the
rotary compressor from a 90Q, which also requires the lines, brackets,
and Oil filter adapter. All said and done, the system is putting out 44
degrees from the vents at 80 degree outside temps. Pretty good, for what
I've seen so far. I've never been able to get it below 40 with the old
setup. If I had the old setup just as it is now(I'll go over those
details in a minute) it would be putting out somewhere around 52-55
degrees. So, I'm pretty pleased.

 

However, in every 4000Q I've owned or driven recently, even with the
heater all the way off (verified under the hood against the stop) the
heater never quits giving out slightly heated air. I've replaced the
heater valve on several of them as well. This current one will be
replaced, as I have a new one here, but hasn't yet.

 

Looking at the coolant routing, it appears that the heater core runs are
sort of a "bypass" of sorts for the thremostat. So, if that's the case,
maybe it isn't designed to ever shut off completely?

 

So, here's the question, if I completely shut off that coolant flow,
does that create hot spots in the cooling system or engine. I really
can't see how it could, but I want to make sure.

 

With the old system, I did have a set of pinch pliers designed to stop
flow through rubber lines when you are working on them. Examples would
be when you take a fuel hose off the pump, but don't want to drain the
tank. I did that all last year, as that was the only way to get the temp
from the vents below about 55degrees on hot days. I did not experience
any sort of overheating, nor was anything damaged that I know of. But,
I've got a valve setup that I'll be adding to permenantly shut off the
heat during the summers, and I just want to make sure I'm not going to
stop the flow that may be engineered into the cooling system.

 

As always, TIA,

Tony Hoffman

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