A/C Condenser Questions
 

Here I go again poking my stick into the A/C hornet's nest.

I am in Tucson, 350 days with sunshine a year. An effective A/C system is essential if you want to drive year round. Systems from Griffiths and Rennaire are at the top of my list. I am dealing with an '88 Carrera. Each vendor replaces the front condenser with a "desert duty" unit. Makes sense to me. Would it contribute to the system's effectiveness if the old front condenser was mounted in the air blast in series with the new unit. A couple of possible ways to do this. Is the contribution to the system's effectiveness sufficient to be worth the effort?

I get the impression from reading all the A/C threads that having as much condenser area as possible is a good thing. What about puller fans on the engine deck lid condenser? I found a couple from Spal that are only 2" thick so probably not a space problem. Or would the dollars be better spent putting Herr Kuehl's condenser mit fan in the left rear fender cavity?

The fans on the deck will help a little when you are stopped but not much. The fan on the engine sucks a LOT of air. The fans just add the heat to the engine.

I did the Griffith's full dual condenser add on and kept my original front condenser and original rear condenser. I replaced all the hoses and the system flat works. I drove to Monterey, CA and back this summer. As I drove through Needles, CA it was 108. I was comfortable inside. I have been to Savannah, GA in August and my wife asked me to turn the temp up because she was cold.

One thing I noticed was with the two fender condensers the engine runs cooler. A lot of the heat from the AC system is dumped in the fenders not on the engine.

Call Charlie Griffith and he can quote you a full system or whatever will fit your needs. It is the best quality parts and the clearest instructions on the planet. If flat out works as advertised. It is not cheap but your car will be drivable year around.

There is NO aftermarket front lip condenser that will improve, overall, the front lip condenser efficiency. They are all structured to mostly BLOCK the front to back "at speed" airflow. They will have more efficiency from the downward flow but there better solutions. The fender well condenser/fan being the best of those should all else fail.

Your car has cabin heating control module that has a somewhat unique aspect. It will automatically turn on the cabin heat blower in the engine compartment should the engine oil temperature rise to the thermostatic switch setpoint and the engine RPM is consistently in the lower ranges.

Trinary pressure switches are priced pretty much equal to the binary pressure switches that are virtually a requirement when converting to R-134a, so I would suggest you have a trinary switch installed and use the third switch element to control the cabin heater blower in the same manner.

Glen already mentioned it above, but to reiterate, the two component changes that made the biggest difference for me were the addition of a fender condenser (with fan) and a serpinetine evaporator.

Also important is to achieve the perfect refrigerant charge (all moisture evacuated from the system - takes a lot of time to do this with a 911 system - and a charging technique that focuses on lowest achievable vent temperatures within acceptable pressure ranges). I can elaborate on my charging method (learned with help from others and successfully repeated time and again) if you would like me to, but the thread will then likely take on some stink when West chimes in to say my method is "foolish" (no matter to him that he hasn't tried it or that I've demonstrated excellent results with it). That's part of the "hornet's nest" effect you mentioned! :D

"..The fans just add the heat to the engine..."

How can that be? Any HEAT produced by the rear lid condenser will ALWAYS flow through the engine. The only difference is that the SPAL fans will serve to even out the flow and continue to cool the rear lid condenser in that low RPM operation range.

Have your car sit in the sun for a few minutes with A/C on and the engine idling... What happens the pressure/heat in the rear lid condenser during that idle period?

It rises...

Now raise the engine RPM and "wick" away that HEAT previously stored in the rear in the rear lid condenser volume.

If you can fit even one SPAL fan onto the condenser to move more cooling airflow downward through the condenser, all to the good.

Most owners who have that SPAL fan DIY run the fans only with the compressor clutch engaged. Since the PRESSURE and HEAT does not magically disappear with compressor off it would be better to use that trinary pressure switch I Mentioned before to run the fans ONLY when the high side pressure warrants.

Yes, you can charge the system somewhat under the optimum, and get vent temperatures under the freeze point. But as owners who have done this admit, you MUST be sure and raise the thermostatic switch setting in order to prevent evaporator freeze up.

How is that done, what guideline?

Your guess is as good as mine...

Note the decrease in system airflow as the evaporator freezes?

^^^ The OP will not have to worry for a second about evaporator freezing since he lives in Arizona - just as I do not living in North Texas - if his system is sound and is charged with a goal of high system performance.

And speak for yourself regarding "guess" - I'm long past a/c guesswork.

Glen---
Good point about transferring the condenser's heat rejection location to outside the air stream that cools the engine. Particularly important for hot climate operation. I had not previously considered that. Thanks.

I did the full Griff's on my 88 cab with four new condensers (front, rear, 2x LR Wheel well), new compressor, r/d, hoses, hurricane fan, and evaporator. My existing system was shot with little useful left. My heating system was shot as well. After the mod I have driven it in Texas, Florida, southern Virginia, and Hawaii with great results with outside temps in high 90s and low 100s. Typical settings after about 10 minutes of full cold/full fan (have the Griff's variable fan) were to back off to about 2/3 full cold and 2/3 full fan. Wife asks for me to turn it down as I like it very cold. I've had my back rear plastic window on my cab fog up due to the cold. Used it briefly in Germany this summer and I think I will need to add a bit of freon this coming summer as my vent temps were in the high 30s and I'm used to high 20s/low 30s. Installed it in 2008. Had a problem with my evap freezing up all the time but it turned out to be an incorrectly placed temp sensor. Once I moved that, I haven't had an issue since. Great customer service...even called on a weekend when the compressor clutch didn't work on a Sunday after picking my car up after an engine re-build. Griff talked me through troubleshooting leading me to find the shop had not reconnected the the hi/lo pressure switch. Plugged it in and ice cold air. Expensive, but worth it.

One thing to do for sure is even if you don't replace the evaporator (I recommend that you do) is to pull the old evaporator. Mine was gross and there was no real option but to replace it with a new serpentine unit.

http://forums.pelicanparts.com/uploa...1418827932.jpg

I am sure it had never been out of there since the car was new.

I'm your neighbor to the north (Phoenix area) so I see similiar, if not a bit hotter temps than you. I went with RetroAir kit that replaces the stock heavy and less efficient rear copper tube and fin condenser with an aluminum parallel flow channel condenser. I daily drive my car, including summers, so that should be testamonial enough.

I addapted it to fit in a fiberglass ducktail decklid as well.
http://i906.photobucket.com/albums/a...asyover/c2.jpg

Use of the cabin heater blower as I described will also redirect rear lid condenser HEAT around , bypassing the engine, removing exhaust manifold radiant heating effects on the cylinder jugs at the same time.

While I am somewhat of an advocate for a (single) wheelwell blower/fan I should point out that the rear lid condenser inlet area is, and will forever remain, the HOTTEST point in the refrigerant condensing cycle. So the A/C heat load on the engine will not be lowered as much as one might first think.

On the other hand the peak high side pressures will be significantly lowered, lowering the temperature at the rear lid condenser inlet.

hoss,

I'm in Tucson also, if you're interested I can tell you from personal experience what worked for me. Shoot me a PM and I can give you the details sans the noise.

IMHO the best installation of a front condenser is the one that Beck's European in Scottsdale does. They use a 964 front condenser. You can not do this as easily on a long hood, but for an 88 it is great.
I have a pic, but it is to large to load

maybe this timehttp://forums.pelicanparts.com/uploa...1418935150.jpg