[DeTomaso] A/C test results

Wed May 15 09:01:46 EDT 2013

 Fan is pulling air into condenser.  Several have questioned whether I have too much R-12 in the system which is causing too much pressure at high compressor rpms.   There may be something to that thought but I'm trying to reconcile how that stacks up with the fact that I was seeing 42 to 48 degree air at 70+ mph for the whole return trip at slightly cooler ambient temps and no direct sun.  At those same speeds on my trip to the car show with the sun shining through the windshield and temps almost 10 degrees hotter the system shut down.

I think I'll have the R-12 level as the next step.
Tom
#5186

-----Original Message-----
From: Rob Dumoulin <rob at dumoulins.net>
To: Tom Shinrock <tmshinro at aol.com>
Cc: DeTomaso Mail List <detomaso at poca.com>
Sent: Wed, May 15, 2013 7:35 am
Subject: Re: [DeTomaso] A/C test results

Could the reduced cooling be also affected by engine speed rather than strictly airflow?  Could you have too much Freon in the system and the increased speed raises the pressure to the point that the shutoff valve kicks in?  Just a thought.

Also - sanity check. The fan is pulling air into the engine compartment, not pushing it out, right? 

I know it has been discussed that at speed there is low pressure behind the car. Has anybody done test to see if there are any conditions that create a similar high pressure in the rear hatch space around the condenser fan?  A severe high pressure area there would have the same effect.  

Rob 

On Tue, May 14, 2013 at 10:17 PM, Tom Shinrock <tmshinro at aol.com> wrote:

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

_______________________________________________

Detomaso Forum Managed by POCA

DeTomaso mailing list
DeTomaso at poca.com
http://poca.com/mailman/listinfo/detomaso