Automotive Air Conditioning Information Forum (Archives)

amphicar770 on Mon June 20, 2011 7:56 PM

Year: 1995
Make: Alfa
Model: 164
Engine Size: V6
Refrigerant Type: R134
Country of Origin: United States

Hi All,

For my Alfa, I just received what the Alfa specialty shop advertises as their greatly improved condenser. Unlike the original, this one is a parallel flow unit. So far so good.

The problem (perhaps) is that the replacement condenser is a good bit smaller than the original unit. I do not know if the smaller size will offset any efficiency gain. More important, what does this mean for how much R134 should go into the system? Am I introducing an ink own variable that will cause all sorts of headaches?

Thanks,

Mike

bromodragonfly on Mon June 20, 2011 8:55 PM

Condensers are rated for a specified capacity of heat rejection, with a condensing temperature X degrees above ambient. You'd need to get in touch with someone at Alfa to see what exactly that rating is, and how it compares to the original to be absolutely sure. It is entirely possible to have a smaller parallel flow condenser with better usable surface area, and have it perform to the same standard as the other. I would hope that the Alfa specialty shop advertises and sells a product that works as it should.

Do you have a system with a liquid receiver and TXV? If so, you are not critically charged, and therefore have some play in the amount you put in.

On a direct expansion system that IS critically charged, under part-load conditions, the condenser's full capacity is not needed anymore, and it will begin to accumulate and store liquid. You will most likely need to reduce the charge, to avoid running out of condenser volume under low load conditions. If the condenser became too backed up, this would result in higher system pressure on both the high and low sides, and the system would eventually cut out on high pressure. I do not have enough experience with variable volume compressors to know how well they would compensate for the above circumstance at all, and if they would sense and adjust flow volume to the degree needed.

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There is no knowledge that is not power

amphicar770 on Mon June 20, 2011 10:05 PM

It has a poa valve and an expansion valve. The parallel flow condenser is an aftermarket unit.

bromodragonfly on Mon June 20, 2011 10:37 PM

Hopefully someone else can chip in. The POA valve limits compressor suction on the evaporator, therefore maintaining a set pressure, and above zero temperatures in the evap so it doesn't ice up. It is my understanding that they are used on systems where the compressor runs continuously, and doesn't rely on a low pressure switch for cycling. If this is the case, and the compressor is always running, I would still worry accidentally overcharging and backing up liquid within the condenser. However, if you have a high pressure cutout that works properly, it should account for this before any damage is done.

I am mostly used to TXV systems containing a liquid receiver, but I know there are TXV systems that are critically charged. I take it you don't have a receiver?

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There is no knowledge that is not power

TRB on Tue June 21, 2011 12:44 AM

Depending on the type of PF condenser. Lots claim they make a PF condenser. Simply by the way the refrigerant flow through the condenser.

With that said. Size to size a real PF condenser is about 1/3rd more efficient. When comparing it to a T & F condenser.

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amphicar770 on Sat June 25, 2011 1:19 PM

Thanks for all the replies. However, the question, which I probably did not state clearly is.

System call for a 42 oz charge. However, the new (aftermarket) pf. Condenser is about 2" x 2" smaller than the original unit. Should I thus adjust the charge amount and by how much?

Thanks.

bohica2xo on Sat June 25, 2011 7:36 PM

The charge level should not change drastically. Your receiver / dryer has a charge "window" of a ounce or three, depending on it's relative size.

Giving up 2 inches on each axis for a high efficiency condensor is not a big deal. It could in fact have more area, since the u-turns on a tube & fin unit waste a lot of space anyway.

The big thing to look out for is coupling. Make sure all of the heat exchangers in the stack are coupled to each other, and the fan assembly. If the airflow can bypass the condensor because of a gap at it's edge it will degrade performance, especially at low speeds or stopped.

With all of the work done on your system (some of it by butchers), you may have an excess of oil in the system. Not uncommon for this to happen with multiple mechanics each "adding an ounce" of oil "to be safe". Too much oil will produce the conditions you seem to have - high head pressures & poor cooling.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.