[DeTomaso] A/C test results

[Mikael]

I second that. Crusing, stop and go and racing in France in summer, A/C
worked fine, with (I think) orig condenser and fan, rotary compressor, full
of R134. I guess the easy answer to your problem is that when it gets
hotter, your (for some unknown reason) less efficient system has to work
harder, has to be turned on more by the thermostat, raising pressure?

First, make sure you have the right amount of R12 in there, too little is
bad, too much is bad.

Mikael

-----Oprindelig meddelelse-----
Fra: SG [mailto:sdlgibson at sbcglobal.net] 
Sendt: 15. maj 2013 18:25
Til: detomaso at poca.com; Tom Shinrock
Emne: Re: [DeTomaso] A/C test results

Tom,
          Here in Ok. where the temps hit 100-105 regularly during the
summer, my system stays in the 40-42 deg. range when on the interstate at
75-80 mph.  I usually have to turn the blower down to be comfortable.  I
have the stock fan and shroud, but I did replace the condenser with after
market, and I have one of the mini compressors.  I also sealed the bottom
edge of the shroud to the rear valance to enhance airflow through the cond. 
My system is also on R134.
 
 Shaun G. 

--- On Tue, 5/14/13, Tom Shinrock <tmshinro at aol.com> wrote:


From: Tom Shinrock <tmshinro at aol.com>
Subject: [DeTomaso] A/C test results
To: detomaso at poca.com
Date: Tuesday, May 14, 2013, 9:17 PM



Here are the results of my A/C test after I had switched back to my stock
condenser fan.  As you recall my A/C basically didn't work during my drive
to Phoenix where we were cruising any where from 75 to 95, but it did go
from 90 deg to 60 deg air in the casino parking lot when it was close to 90
deg (with the aftermarket fan).

Last night we set a record low temperature of 34 degrees.  Today we are
pushing hard to beat the record high of 96....crazy!  I tested my car at 3pm
when the temp was 93.   Backing out of the garage, the temp probe in the
left vent read 80 degrees.  I turned on the A/C and after less than 2
minutes was seeing 36 degrees on the probe.  After about a mile I turned
onto the highway.   At 55mph the air temp went up to 40-42 deg.  After about
30 minutes it was at 50 deg.  I increased my speed to about 65 and saw the
air temp go up to 55 deg.  At the 45 minute mark I turned onto the
interstate and raised my speed to 70 - 75 mph.  The air temp went up to 60 -
62 degrees and basically stayed there for the 15 minute drive back to my
house.  I could hear the relay clicking on and off, so I assume that I was
bouncing against the high pressure cut off switch.  I backed my speed down
to 65 and saw a small drop in air temp, maybe 58 deg.  I got off  the
interstate and in the mile drive to m y house at 35 mph saw the air temp go
down to 55 deg.   I let the car idle for about 10 minutes when I got home
and saw the air temp drop to 45 degrees.  

What this tells me is that my A/C works well if the fan can pull enough air
through the condenser.  The fan performance goes down at high temps and as
the speed goes up because the air gets turbulent at the rear of the car. 
This aligns with what I've heard others say about the A/C going south after
75 mph.  I was told by an A/C shop when I converted my Porsche 944T to 134
that an A/C system is operating as good as it can if it can put out air that
is 40 deg cooler than ambient temperature.  So getting 62 degree air on a 93
degree day made me feel kind of good.  Unfortunately with only 2 vents (with
the left one misaligned by about 30% from the opening in the heater box) and
only 2 fan speeds there isn't much air movement so 60 degree air is just
marginally comfortable.

About an hour later I drove the car to a car show that was a 90 minute drive
down the interstate at 5pm where the ambient temperature was still 93 deg. 
The air temp started out at 50 deg and within 15 minutes was at 60 deg at 70
mph.  Within another 20 minutes the air temp rose to 80.  Not long after
that the A/C quit working.  Bummer.   The sun was beating right through the
windshield and the temp probe showed 110 deg air coming out of the vent. 
Suffered for another 15 minutes waiting to see if anything would happen and
then pulled the plug and opened the windows.  I noticed at some point, for a
very short time, the A/C came on and dropped the vent air to 85 deg but it
didn't last long. 

The ambient temperature had come down to 85 and the setting sun went behind
some clouds on the trip home (so no sun beating through the windshield).
Turned the A/C on when I left and saw 42 to 48 deg air all the way home at
70+ mph.  So it looks like I've got an A/C that works fairly well as long as
the temperature doesn't get into the 90s.  

So, I'm curious to know if this performance is similar to other's A/C at
similar temperatures.  

I assume I could get more cooling if I went to one of those parallel flow
condensers with the two fans sucking in air.  I'll see how the A/C works
this summer to determine if I want to make the change.

Tom
#5186

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