[DeTomaso] A/C condensor fan test results

[Tom Shinrock]

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