[DeTomaso] A/C condensor fan test results

Sun May 5 09:01:17 EDT 2013

 Scott,

Thanks for your comments.   I don't think my evaporator is icing up because I never saw a reduction in air flow from the fan (which is what I assume you are referring to when you say "blower").  I find it hard to believe that the evaporator could ice up in the near 100 degree heat and ultra low humidity conditions in Phoenix.  I could only wish my system got that cold.  I will, however, do as you suggested the next time it stops working to see happens.  Just curious what is the solution to the evaporator icing up...dial in some heat from the heater?

Thanks,

Tom

-----Original Message-----
From: Scott Bell <scott at saccrestorations.net>
To: 'Tom Shinrock' <tmshinro at aol.com>; detomaso <detomaso at poca.com>
Sent: Sat, May 4, 2013 10:02 pm
Subject: RE: [DeTomaso] A/C condensor fan test results

Tom,

Something else to consider... If the AC works for some period of time and then 
stops working, the problem could be the evaporator
icing over. This is VERY common. To test, next time the AC stops working while 
driving, turn the AC compressor off with the
thermostat knob. Leave if off for 5 minutes or so. During this time the blower 
should still be running. Then turn the AC compressor
back on and see if the AC is again blowing cold. Also, when the evaporator is 
icing over, it is common to have a reduction in blower
pressure. As the evaporator defrosts, the blower air pressure will increase.

Also, the switch you added cuts the compressor off when the pressure gets too 
high or too low, as opposed to, too hot as you stated.
If the compressor is turning off do to this switch, something is indeed not 
right. As you guessed, not enough air flow through the
condenser on a hot day will cause the pressure to go to high and shutoff the 
compressor. This condition causes hoses to blow off on
systems without a pressure switch.  

Scott

-----Original Message-----
From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com] On Behalf Of 
Tom Shinrock
Sent: Saturday, May 04, 2013 7:38 PM
To: detomaso at poca.com
Subject: [DeTomaso] A/C condensor fan test results

Those I met at the fun rally probably got bored/annoyed with my stories of my 
air conditioner not being effective on my drive from
Iowa to Phoenix (believe me....I heard about it from Dena on the drive back).  I 
had the system filled will R-12 before I left Iowa.
I put in a new rotary compressor and drier last summer along with a high temp 
cut off switch. Before that I never tried to get my
A/C working.  I was pleased to find a number of people that claimed to have 
effective A/C with rear mounted condensers so I have
hope that I can get mine to work.

Gil Mares and Les Gray went out of their way to look at my system and put me in 
touch with some A/C experts in Phoenix.  To shorten
a long story, when Les looked at the system we found that the A/C worked in the 
parking lot blowing 60 degree air with ambient temps
around 100 in the car.   He didn't see any bubbles in the drier site glass.  He 
also noted that I had original hoses.  I called the
experts that Gil had referred me to and gave them the results of the parking lot 
test.  Their opinion was that no bubbles indicated
that the system was fully charged and the fact that  the A/C worked in the 
parking lot but not on the highway suggested that the
condenser was not being taking enough heat out of the system which was probably 
due to a underpowered fan and/or an ineffective
condenser.

On the way home I would periodically turn on the air and find that it would blow 
cool air for a very short time and then stop
working.  On my last day of driving I ran the A/C in the late morning before it 
got crazy hot and found that the air actually worked
for about an hour and a half before it quit working.  During that stretch I 
heard a sound I've rarely heard; the A/C relay clicking
on and off.  This experience pushed me further to the conclusion that my 
condenser wasn't pulling enough heat out of the system and
when it got hot enough my cut off switch was shutting down the compressor.

I replaced my stock condenser fan with a new fangled one last summer thinking it 
would be better.  Since then I've read many
opinions that the stock fan moved more air.  John Buckman described to me how he 
tested various aftermarket fans using increasing
amounts of cardboard at the condenser grill to determine which fan provided the 
most suction to hold the cardboard in place.  He
said he did not conduct that test for the stock fan however.

Feeling that my A/C would be more effective if I could move more air through the 
condenser, I decided to perform the cardboard test
to see how my aftermarket fan compared to the stock fan.  Here's what I found:

With my aftermarket fan installed I cut a piece of cardboard the size of the 
grill opening and turned the fan on via a battery
charger and saw that the fan sucked the cardboard and held it to the grill.   I 
then taped more and more cardboard to this first
piece of cardboard until the fan could no longer provide enough suction to hold 
the mass of cardboard against the grill.

I then removed the aftermarket fan and re-installed my stock fan (by the way 
both fans had dense foam stuffed into the sides of the
fan shroud to seal the gap between the shroud and car body to prevent the fan 
from sucking any air from inside the engine
compartment).  I found the stock fan could easily hold the mass of cardboard I 
ended up with when testing the aftermarket fan.  I
then proceeded to add more and more cardboard until the stock fan could not 
provide enough suction to hold the mass of cardboard to
the grill.  Both tests were performed with the tub out.

I don't have a scale small enough to weigh the different amounts of cardboard to 
quantify the difference in weight but I did
calculate the equivalent area of card board that each fan could hold.  The 
aftermarket fan held 677 square inches of cardboard and
the stock fan held 782 square inches (15.5% more).  So obviously I was not 
getting as much condenser cooling with the aftermarket
fan.

I then proceeded to test the A/C with the tub in.  I put a temperature probe in 
the dash vent which indicated 70 degrees ambient.  I
turned the A/C on saw that the vent air temperature was an indicated 25 degrees.  
I won't really know how good it performs until we
get some hot weather around here.

I heard a lot of people talk about parallel flow condensers.  I know I don't 
have a stock condenser but I don't really know what
kind came with the car.   When I was switching condenser fans, I took a closer 
look at it and I'm wondering if it is a parallel flow
design.   I took some pictures of it to see if someone can tell me what I have. 
http://poca.com/index.php/gallery/?g2_itemId=40199

Any and all comments are welcome.

Tom
#5186

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