Dual parallel flow condenser '83 300SD - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 09-14-2017, 03:14 PM

I am working on a project for a friend- installing a dual
parallel flow condenser setup on his 300SD. He is getting the Sanden retrofit as well. A custom fitting is needed for connecting the two condensers in series. It has a #6 Oring fitting on one end, and a #8 hose barb on the other.

I am waiting for the 16X24 condensers to arrive. I will post my progress and photos.....Rich

greazzer · #2 09-14-2017, 04:05 PM

Pretty awesome ... so, it should blow ice crystals ?

ROLLGUY · #3 09-14-2017, 04:47 PM

Quote:

Originally Posted by greazzer

Pretty awesome ... so, it should blow ice crystals ?

Correct, so I hear. I hope to find out pretty soon........Rich

ROLLGUY · #4 09-25-2017, 08:39 PM

I started mocking up the condensers and fan/s today. There is plenty of room for both condensers, but the fan/s are a different story. I tried a dual fan unit from a 190E first, and there was no way it will work and still be able to close the hood. I then tried a second gen 126 fan, and I think it will work with a little modification to the grille. I got two of the three condenser hoses made. I need to finalize the mounting of the condensers before making the other hose. Thinking about the flow from one condenser to the other, I figured it best to plumb the discharge hose from the compressor to the second (rear) condenser first, and then to the first (front) one. That way the refrigerant gets mostly condensed before going to the front condenser that gets the coldest air. I think it will be less efficient the other way (front first).

DeliveryValve · #5 09-25-2017, 09:30 PM

Is the fan hub hitting the grill? If so, You'll need the flat hub Bosch 2nd Gen w126 fan if you don't want to modify the grill.

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BillGrissom · #6 09-25-2017, 11:35 PM

Quote:

Originally Posted by ROLLGUY

... I figured it best to plumb the discharge hose from the compressor to the second (rear) condenser first, and then to the first (front) one. That way the refrigerant gets mostly condensed before going to the front condenser that gets the coldest air. I think it will be less efficient the other way (front first).

Correct, from what I recall in engineering school. I was an ME, but overlapped w/ ChE's, and they have a standard class "Unit Operations" which covers this. Your approach is closer to a "reverse-flow" exchanger, which is more effective than a "parallel-flow" one. Wikipedia should have more.

As you know, stacking condensers in front of each other gives diminishing returns since the air flow is reduced. Probably there is a point where another condenser would give an adverse effect. But, 2 is probably better than one.

tjts1 · #7 09-26-2017, 01:53 AM

I would do a single large puller electric fan behind the radiator and ditch the aux fans all together. You want to expose as much frontal area to oncoming airflow as possible. Aux fans just block airflow once you have a powerful enough puller.

Turbo300Mercede · #8 09-26-2017, 08:56 AM

Quote:

Originally Posted by ROLLGUY

...Thinking about the flow from one condenser to the other, I figured it best to plumb the discharge hose from the compressor to the second (rear) condenser first, and then to the first (front) one. That way the refrigerant gets mostly condensed before going to the front condenser that gets the coldest air. I think it will be less efficient the other way (front first).

I agree with this thought. The hottest refrigerant will be coming out of the compressor, you will be using the heated air passing through the front condenser to reduce that refrigerant temp, while the now cooler refrigerant will be reduced in temperature by ambient air flowing across the front condenser.

This is the same principle as an opposing flow "tube in hose" heat exchanger.

I am following this thread with much interest. The A/C on my 87 300D with the original condenser is lack luster at best. I have toyed with the idea of installing a parallel flow condenser off a late model vehicle, to replace the original tube and fin condenser. You are taking this to the next extreme!

Thanks for the posts.

ROLLGUY · #9 09-26-2017, 11:07 AM

Quote:

Originally Posted by DeliveryValve

Is the fan hub hitting the grill? If so, You'll need the flat hub Bosch 2nd Gen w126 fan if you don't want to modify the grill.

.

I have a 2nd Gen 126 fan (in the photo). Is there one that is thinner yet?

ROLLGUY · #10 09-26-2017, 11:14 AM

Quote:

Originally Posted by tjts1

I would do a single large puller electric fan behind the radiator and ditch the aux fans all together. You want to expose as much frontal area to oncoming airflow as possible. Aux fans just block airflow once you have a powerful enough puller.

I thought about that too. I will talk to the owner and see if he is willing to spend the $ for a puller fan. It may be best to get one from a wrecking yard, rather than new. This may be better still, since I don't know how good the fan clutch is. If it needs to be replaced, that is money saved on the purchase of a puller fan.

Air&Road · #11 09-26-2017, 11:16 AM

Wow! Does this guy live at the equator?

I am putting a 300E back on the road that has dual fans, but was originally R12. It is a '92 model I think. All I know yet is that the system is tight. I am hoping that it was a model with some changes leading up to 134. Apparently the evap is okay, but it will be awhile before I know if it will need a podectomy.

I hope I don't ultimately have to do dual condenser mod, but I will watch this thread closely.

Air&Road · #12 09-26-2017, 11:22 AM

Quote:

Originally Posted by ROLLGUY

I started mocking up the condensers and fan/s today. There is plenty of room for both condensers, but the fan/s are a different story. I tried a dual fan unit from a 190E first, and there was no way it will work and still be able to close the hood. I then tried a second gen 126 fan, and I think it will work with a little modification to the grille. I got two of the three condenser hoses made. I need to finalize the mounting of the condensers before making the other hose. Thinking about the flow from one condenser to the other, I figured it best to plumb the discharge hose from the compressor to the second (rear) condenser first, and then to the first (front) one. That way the refrigerant gets mostly condensed before going to the front condenser that gets the coldest air. I think it will be less efficient the other way (front first).

Yes, flow through the rear condensor first. Also, make sure you seal around the edges with foam door stripping or something to force air through the second condensor. You may also have to weatherstrip between the rear condensor and radiator to force air through rather than it exiting around the edges starving the radiator of airflow.

DeliveryValve · #13 09-26-2017, 11:28 AM

Quote:

Originally Posted by ROLLGUY

I have a 2nd Gen 126 fan (in the photo). Is there one that is thinner yet?

Why yes, yes there is. Pic of my w123 with a 2nd gen w126 fan..

.

Air&Road · #14 09-26-2017, 11:49 AM

Looks good Delivery!

Diseasel300 · #15 09-26-2017, 11:57 AM

I'm curious why this kind of wheel reinvention is required? A GenII W126 with the small tube condenser running 134a is perfectly capable of keeping up with 95˚+ temps. With a single parallel flow condenser, I'd expect the performance to be nothing short of flawless.

By doubling the condenser surface, I'd be concerned about taking TOO MUCH heat out of the system, especially in low ambient conditions. There is a point where you can subcool the refrigerant to the point that overall system performance takes a nosedive. Modern central A/C systems compensate for this by using enormous indoor coils to give the refrigerant time to boil off.

I'd be concerned about flooding back to the compressor, especially in lower ambient conditions, but that's just me. The refrigerant actually does need a certain amount of heat in it to do work. If you pull too much heat out, it will actually reduce performance. A bit counterintuitive.