Warm Temps Highway/Cool Weather and Flooding: SOLVED

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Year: 1992
Make: Chevrolet
Model: Caprice
Engine Size: 5.7
Refrigerant Type: R12
Ambient Temp: 85
Pressure Low: 38
Country of Origin: United States

A little background first. I live in South Florida, just north of Fort Lauderdale. We have some of the worst conditions for the performance of AC, as we not only get blistering temps, but that is constantly backed up by humidity that is generally a minimum of 80%, and routinely hits 95%+.

The problem I have been having is that when temps are at their hottest, I get solid 42-45 degree vent temps, and then as it gets cooler outside, or rains, my vent temps climb to 60 degrees. Not that I'm complaining that when it's 99 outside, with humidity over 90%, I am sitting in my wagon feeling like I need to grab a wool coat and mittens. It just rankles me that if I get on the highway, if the temps are cool, or if it rains, the AC gets warmer. It's still cold enough that I want to point the vent away from my knuckles, but still.

So, today, with temps hovering between 85-88 degrees, with humidity of 85%, I decided to test my system in a few ways. Here's the details:

Ambient: 87 (average)
Temp Entering Condenser: 89
Temp Behind Condenser: 124
Cold Line Temp: 44
High Line Temp: 160
Vent Temp: 49-50
Low Side PSI (@ Idle): 38 psi

Obviously, the high temp was quite ridiculous, looking at the R12 chart. So I decided to experiment. First thing I did was idle the engine up to 1500 rpm. Low Side pressure dropped to 22 psi. OK, so maybe bad compressor? Maybe. But I have been deeply suspicious of my OEM fan for some time. Besides the fact that the fan appears to be a pure centrifuge, sending exactly no air in backwards flow, but flinging it outward instead (which is nice, since a good percentage of that flinging air remains in the fan shroud), I also discovered under smoke test that air actually flows forward to the engine fan. So, I decided to do the mist test to see what would happen. I barely cracked open the spigot, and let a fine mist travel toward the condenser. Results? Low side dropped to 21 psi, hovering just above cutoff. Next, I idled up the engine to 1500 rpm. Never made it. AT 1100 rpm, low side pressure sank to 18 psi and the compressor cut off.

No big shock here, because early this morning, when the air was kind of cool, I heard the compressor cycling.

So, next step was the paper test. I took a small piece of paper and set it close to the condenser to see how easily it would take. It didn't take the paper real fast, and didn't stick real hard, either. My Ram and Charger would take that paper right out of my hand. Clutch fan roars like a lion when the heat hits it, so it's not that. This steamboat paddle wheel of a fan just sucks, or doesn't suck, rather.

So, the long story made short here, is that any time the condenser is actually getting decent airflow, the true state of being undercharged is revealed, and the compressor just cycles it's butt off, causing temps to rise. Rain, cool ambient, highway, whatever. Warm, warm, warm.

Well, fortunately, I already have a set of truly high flow electric fans ready to go in, and then I can get this system charged up the right way.

Now, while all of this was going on, I started looking at my drain tube, wondering where in the heck the big puddle of water was that I should be seeing under it. Well, I found it under the mid-section of my wagon, leaking down from the rear seat area. WHAT THE ____?! Well, that little drain tube was letting all of the water dribble down it's bottom, back through my firewall, under the carpet, under the seat, and down through the rear seat footwell body plug. Good thing my wagon averages 110 degrees during the daytime. It's going to need drying out big time.

I put a section of hose on the end of it, angled it down, and made a P-pipe drain, like are installed on the big residential and commercial units. Runs like a faucet, and now directly to the ground.

Sheesh. What a day.

OK, today, I took the electric fan set that I am about to install in my car, and set it loosely in front of the condenser to see what would happen. Low and behold, low side pressure immediately dropped 10 psi. With them set up in their most efficient state, behind the radiator, they should be kicking butt and put this problem to bed for good.

Solution confirmed. Poor airflow through condenser due to inferior engine fan.

i have seen a fan for a V pulley, on a serpentine water pump,.

the rotation is wrong on a V pulley,.

I've spent plenty of time observing this fan, wondering how it is that it has angled blades, and yet, produces apparently no backward pressure of air. I can only conclude that this fan was engineered as a purely paper design, and received zero aerodynamic research or development. I checked just now again, and yes, it rotates in the correct direction.

The way the blades splay out toward the tips is most curious. From what I know of aerodynamic design, you pretty much cannot come up for a better way to destroy the efficiency of the fan. This is why modern engine driven fans, like the one on the Trailblazer, have a hoop that encompasses the entire circumference of the fan disk. Major increase in flow and efficiency.

Maybe the fans in these Caprices are just 1950s/60s designs, flipped over for use as serpentine fans.

Trailblazer fan:


My piece of garbage:




Something of a difference there, no?

This is a good reason to put 93 FW electric fans on B-bodies.

Aren't the ends of those fan blades supposed to be flat? They should be tight inside the shroud, and if they're not, it would perform exactly as you are saying.

How about trying this one?

http://www.ebay.com/itm/New-Flexalite-Fan-Blade-SaVana-Full-Size-Truck-GMC-G2500-Van-G3500-5919-/370930746248?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1992|Model%3ACaprice&hash=item565d320388&vxp=mtr

They should be flat, but the fan in the pic, my fan, and every other Caprice fan I have ever seen has those tapered tips.

I'm done with mechanical fan. If I were going to play with mechanical, I'd get that Trailblazer one before I'd get another heavy steel finger chopper, but I have a REAL nice set of electric fans just waiting to go in.

Just have to get my axle sorted out first.

So that is a caprice lo5 fan?

thats odd,.

Yeah, that weirdo thing is the Caprice L05 fan. Go figure.

I've been doing some mental gymnastics trying to remember my 92 and other L05 engines. I believe that fan is the correct orientation, if the picture is of the fan as sitting in the driver's seat. The engine rotates CCW, as seen from the driver's seat. The fan pulley should be driven off the back (ungrooved) side of the belt if the belt is routed correctly, so the fan actually rotates CW. (NOTE to LT1 owners: the mechanical fan in the towpack cars is driven from the grooved side of the small belt and rotates the same direction as the engine: CCW). Flipping the fan will not change the direction of airflow or rotation, but will affect the efficiency (especially with a curved blade!)

But, all that said: the blades look like they are bent in the photo. The flare at the tips should be progressive and smooth and face forwards (towards the radiator). The flare functions, as I understand it, to smooth the airflow at the tips and reduce noise. I wonder if someone bent the tips to make a larger fan fit in the space, perhaps trying to replace a stock 5 blade fan with a larger 7 blade fan?

The AC drain should have had an elbow on it, for exactly the reason you describe. You should lift the PS carpet and underpad for two reasons: first, it's amazingly thick and absorbent and will take forever to dry. Second, you really need to inspect, dry and/or repair the floor under there now, before it's too late and you have nothing left but a rusty hole.

As for your low side pressures, they sound way too low. 10 psi? The cycling switch should be set closer to 28 - 30 psi for R-12. Much lower than that and you run the risk of freezing up the evaporator fins. The classic symptom of a frosted-over evaporator is the air flow through the fins slowly diminishes to almost nothing. Air flow will recover if the AC compressor is shut off for a while (ie: set climate control to "Vent") allowing the frost to melt and drain away out your new tube.

No, when I used the fans to apply forced air to the condenser, the pressure dropped by 10 psi. It dropped from 40 psi down to 30 psi.

I don't know what they had in mind when they designed the fan blade, but it sure does not work very well.

As for the carpet, I'm going to pull it this weekend anyway, so it will get plenty of time under the flaming sun to dry out top and bottom.

Viceroy454 wrote:

No, when I used the fans to apply forced air to the condenser, the pressure dropped by 10 psi. It dropped from 40 psi down to 30 psi.

Ooops, sorry, I misread that. Dropping the pressure from 40 to 30 pretty much confirms you have inadequate air flow.

However, earlier in the thread you mentioned that the compressor cut out at 18psi. If that is accurate, it's too low. If you are using a cheap gauge from a kit, the gauge may not be accurate of course, some of them are pretty terrible. The objective is to get things down to -just- about the freezing point on the low side and be able to maintain it there, but not so cold the evaporator frosts over and blocks the air flow.

I know it's too low. The lack of idle airflow is creating the appearance of being charged because of the jacked up pressure. I don't want to completely charge the system until that has been resolved, because then when airflow is insufficient, it will be over-pressure, and I've seen that do damage before.