Front AC condensor issue

88911coupe · 08-28-2006, 08:51 AM

I did a search and can't seem to find an answer. Anyway, I was testing to see how much air flows over the front condensor on my otherwise stock 88 Carrera's ac system. I used a piece of burning incense (please, no comments) to see where the air was flowing and how fast. Here's the odd part...the air was being drawn "into" the vent on one side and "out" of the vent on the other. I assumed all the air across it flowed the same direction...is mine working as normal? It all appears to be hooked up correctly inside the trunk with no missing or damaged parts that I can see.
TIA

cmonref · 08-28-2006, 04:20 PM

With the fan running, the air is normally directed directly downward a few inches behind the front bumper. Look under the car for a metal grill that protects the condenser from road hazards like rocks. You should be able to feel the air coming out.

If no air comes out and the fan is running, take the fan off of the mount. Run the fan and see if the air comes out of the scroll housing. If you have air flowing at this point, look down into the shroud and see if there is a rag or other blockage that is preventing air from going thru the condenser.

curiousone940 · curiousone940's Garage

Ditto on what Brian said.

88911coupe · 08-29-2006, 09:31 AM

What is odd is that I get air flowing down (towards the ground) on the left/driver section of the evaporator but on the right/driver's side the flow is back into the evaporator. I'll just remove the fan housing and see if there is some sort of blockage.
Thanks

cmonref · 08-29-2006, 10:08 AM

Your initial post mentioned the front condenser. Now you mention the evaporator. The front condenser is down by the spare tire. The evaporator is behind the gas tank under the carpet and under the door at the aft end of the front trunk area.

Which one are you talking about?

88911coupe · 08-29-2006, 10:49 AM

I'm sorry...it's been a long day. I am referring to the front condensor, the one behind the front bumper, not the evaporator in the smuggler's box.
Thanks

cmonref · 08-29-2006, 11:11 AM

Heat and long days fog the mind. Let us know what you find.

Mysterytrain · 08-29-2006, 12:07 PM

I think its normal. That front blower assembly is an odd design. I would guess that all the blow is directly under the squirel cage. The long funneled housing was an attempt to spread the flow but I would bet the closer you get to the spare tire the more in sucks air up from the bottom.

Barrpete · 08-29-2006, 02:24 PM

If the '88 is the same as my '86 the hole beneath the blower is not as long as the condensor, in fact it's only about 1/2 the length. And since the fan is mounted on the drivers side, it could cause some quirks with how the air circulates.

Although I would expect you would get pretty even flow front to back as the condensor is only about 5" or so front to back. Left to right I can see having a pretty wide variation in flow. Although the 88 could be different.

Wil Ferch · 01:13 PM

Also oddly...the "inlet" is part of the car's front bulkhead that is completely hidden and covered by the front bumper ( bellows-style bumper). Having a "forward-facing" hole in the bumper with a flex hose attached to the "normal" bulkhead inlet, would....IMHO....be a great improvement.

- Wil

88911coupe · 08-30-2006, 11:46 AM

Wil,
I noticed that as well...really doesn't seem very well designed. I can' help but think a more robust airflow over the condensor would help. It would probably help also if I had one of those aftermarket versions which are parrallel flow or whatever they call it. We've had a cold front here in Dallas (highs in the LOW 90's...break out the sweaters!) so my ac is actually doing an adequate job. Hopefully we aren't going to see too many more +100 degree days. I think though my first improvement will be a procooler to see what that does.

Mysterytrain · 08-31-2006, 07:25 AM

My half assed attempt at drawing what I think is happening to the airflow over the front condenser.

88911coupe · 08-31-2006, 07:43 AM

Ron, Your diagram demonstrates EXACTLY what I am seeing. In addition, it seems to me that the air that comes INTO the condensor is going to end up transferring some portion of the heat it's drawn away right back into the condensor. Maybe some of the fluid engineers could chime in. Do we have some room for improvement here? I'd hate to add and expensive aftermarket condensor and then have its effectiveness crippled by Porsche's design limitations.

hcoles · 09-04-2006, 09:19 AM

great thread....maybe some smartly placed baffles can be installed to get the flow to be evenly distributed across the heat exchanger...again we run into wonderful German engineering for the AC

not long ago I took the fan out and sprayed cold water over the hex to see if the air got colder inside...my recall is that it didn't do much... but I need to do again. I'm also thinking of putting thermalcouples on the incoming and outgoing pipes to that hex and see what the delta T is while driving down the road and sitting still with that fan running.

I did see some company sells a "bigger" hex for the front...that should help as well but the reverse air flow, if it happens and it looks like it does, is a block to getting good performance I think

kuehl · kuehl's Garage

Quote:

Originally Posted by Mysterytrain

My half assed attempt at drawing what I think is happening to the airflow over the front condenser.

Yes Ron. What you sketched is pretty close to what is happening.

We ran several smoke tests and a did a grid array of anemometer readings and the flow is almost close to what you suggested.

You might consider there are a few problems with the front condenser air plenum below the fan, such as the unequal distribution of air or the recirculation; actually there is recirculation on the LH side too. And you may consider that a simple "baffle" or deflector could overcome some of these issues however certain baffling designs or placements create eddies which further reduce performance (you can verify this with smoke and an amp meter connected on the fan motor).

The current blower design is what it is for a few reasons: (i) the size limitations or foot print in the front trunk area (adjacent spare tire, battery, etc.), and
(ii) the performance of the squirrel cage fan vs. other fan types.

Small DC axial fans (such as what you find on a computer power supply or in a computer case) do not come near the cubic feet per minute of the present design. A faster spinning motor might help a bit, but there is the "cost vs. benefit" scenario, assume you want to double the cfm you may need turn up the rpms a bit more than you would expect. You can get a better idea of the the current design cfm with the SAA Fan Test Code or AS2936:1987.

We did a lot of testing with the stock fan and motor when we designed the Kuehl front condenser; one of the obvious observations noted was that a thicker condenser was not better nor was a plate and fin as compared to our serpentine: more important was the number of passes and the fin spacing (too dense of design and you do not get adequate air flow through the coil).

khamul02 · khamul02's Garage

As stated in the other thread there has to be a better way to get more air to the front condenser. Hopefully, in the next couple months I'll have some time to create a 3D model of the available space in that area along with the largest hole possible to the condenser (may need a single back in the center of the hole). I can then pass that on to a fluids phD who's a friend of mine to see if there is a way to fit a small spa fan in that area with adequate intake and flow to the condenser. This of course will require a brand new enclosure probably fabbed out of fiberglass.

But before all that is done we may want to drop the condenser and put a high power (200 to 300 cfm) fan on it to see if it will make that much of a difference.

Do you happen to know what the output in CFMs is for the stock fan?