strange cooling

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grumpy old man
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strange cooling

Postby grumpy old man » Fri Jun 22, 2018 4:49 pm

I have been working on a '63 Pontiac Catalina convertible. In that era a convertible with A/C was a rare thing. Being in So Cal with triple digit days A/C is not an option. I have adapted a unit from a late 90's vintage Ford Crown Victoria, it had all the outlets in a usable location and fit with minimal modification. The size of the radiator is such that I could not find a condenser with adequate capacity for the heat load so I stacked two, one behind the other. I am going from compressor to rear condenser, rear condenser to front condenser and front condenser to evaporator. I am driving all this with a sanborn compressor. the unit works fine in the garage, 40 degrees at the nozzle 200 psi on the high side and the low side cycling off around 12 psi and on around 30 on a 90 degree day.

Here is the issue. on the road above approximately 20 mph the nozzle temp goes from 40 to 60 degrees. I can not figure this out as I can not duplicate the condition in the garage. If I run the engine up to about 2000 rpm which is freeway speed it works fine in the garage, pressures don't vary much other than the high side pressure elevating slightly. The obvious variable is air flow but I have a 3000 cfm electric fan hard against the front condenser wired into the clutch circuit and a 7 blade engine driven flex fan behind the radiator. Everything is shrouded so the airflow should be going straight through the condensers and radiator so I am not sure that airflow is an issue.

The condenser layout is unconventional but I can see no reason why it should not work, the accumulator was replaced at time of installation as it was open and exposed to atmosphere for a considerable length of time. I have replaced the orifice with no discernable change. I am running R134 which was the original refrigerant and those crown vic's always cooled more than adequately on the hottest of days.

Frankly I am at a total loss as to what is going on. Obviously I am missing something but don't know what it might be. Ideas???
71403
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Re: strange cooling

Postby 71403 » Fri Jun 22, 2018 6:13 pm

What are the pressures when it stops working?

Pusher fan can impede airflow been there done that tho usually at highway speed not 20mph. From what you describe it's tied to the clutch so will be on whenever the clutch is on regardless of speed?
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bohica2xo
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Re: strange cooling

Postby bohica2xo » Fri Jun 22, 2018 6:34 pm

Ok, the series condenser should work - we have discussed this one at length on the old board.

But let's get the basics out of the way. Is the engine the original Pontiac 389? A later 455? An LS swap?

Are the engine & water pump pulleys OEM? Aftermarket? Swap to later serpentine?

Is the fan in a shroud all the way around, and at least the leading 1/2 of the blades inside the shroud?

Is the flex fan solid drive?

A proper mechanical flex fan has always been enough here in Las Vegas. Pusher fans have never been needed with the full power of a V8 available to drive the fan.


It sounds like an airflow problem. You could try a temporary air dam under the front bumper to see if some sort of low pressure airflow is causing this.


I am curious what you did with the Crown Vic air box inlets for fresh air & the blend doors etc.


Any pics of the install?

.
grumpy old man
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Re: strange cooling

Postby grumpy old man » Sat Jun 23, 2018 12:33 pm

The crown vic a/c units fit on both sides of the firewall. The defroster duct lined up perfectly. I constructed a fresh/recirculating duct the fits in the old fresh air foot vent on the right hand side. I needed to make a custom fan housing to fit in the available space. The heater discharge is on the bottom I just needed to make a deflector to get the air pointed where I wanted. The outlets are factory Pontiac, not an easy item to find, and are connected to the under dash unit via a custom discharge duct with 2 inch hose connectors. The fan and vacuum switches have been adapted to the original heater control and the temp door is mechanically operated by the original temp cable. All in all it looks like it belongs there. I even had someone that used to be on the assembly line during those years ask me about the "factory air" in a convertible!

The engine is the original 389, I did put in a 4 row aluminum core radiator with the shroud extending back to the rear of the fan blades, solid drive no clutch. original water pump and v belts as there are no aftermarket pulley kits available for anything pre '65. The cavity behind the grille to the radiator header is already sealed. there is sheet metal from the bumper to the radiator header, the header is sealed between the fenders the only thing I do not know because I never thought of it until this morning is how much space is between the radiator header and the underside of the hood, but it can't be much.

I am an old goat not terribly computer literate. I would be more than willing to post as many pictures of the install as you would like if someone wants to lead me through the process.
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bohica2xo
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Re: strange cooling

Postby bohica2xo » Sat Jun 23, 2018 1:14 pm

Well it sounds like you have done quite a bit of work to avoid recirculating radiator discharge air. That is good.

One thing that comes to mind is the cowl vents. I chased a similar problem on an early A body mopar when I lived in northern Colorado. The heater would work ok until I cleared 20 mph. Then things got cold. Turned out the high pressure air at the base of the windshield was overpowering all of the seals in the air boxes & ducts. I looked for days for a hole in a firewall - had a cold draft under the dash. Taped up the cowl vent & it went away.

A quick swipe with some masking tape will answer that question quickly enough.

The next step is road test pressures. Hook up your manifold set & route the hoses so that you can duct tape the gauge set to the windshield. Have a navigator ready to read and record pressures & vent temps as you drive the car. Vary road speeds & engine rpm to build a performance table.

.
grumpy old man
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Re: strange cooling

Postby grumpy old man » Sun Jun 24, 2018 12:04 pm

RE: cowl vent, with the system off there is no air bleed from any vent either dash or heater at any speed. As for the heater, long story but the heater core has been disconnected until last week. This problem predates the A/C problem. And while it would be possible for air pressure to overcome the temp door and bleed air in from the heater side the connection on this door is cable operated and without bending something it is not going to move. In addition before the install I put new foam seals on all the doors to prevent any unwanted air bleed. Driving with the gauges on the windshield was going to be my next step. I have been thinking all morning how to route the hoses so I can duct tape the gauge set to the windshield. The only way I can figure is to shim the hood up so I can route the hoses out the back. there is no other place. No point in trying it today as the weather is overcast and in the 60's.
Will report when I manage to do it.
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bohica2xo
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Re: strange cooling

Postby bohica2xo » Sun Jun 24, 2018 4:13 pm

I have some long hoses for that - on cars with a flush hood sometimes it is easier to come out under the front edge. You can couple R12 hoses with a flared tube coupler.

Shimming the hood hinges with 1/2" spacers & longer bolts works too. It is a lot easier on cars with hidden wipers & a big rubber gasket at the rear of the hood...
grumpy old man
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Re: strange cooling

Postby grumpy old man » Sun Jun 24, 2018 6:44 pm

This thing is starting to make sense. I was putzing with it today and looking at the pressures and the way it is cycling it is acting somewhat like a low charge. I could not get the nozzle below 50 degrees. Just for giggles I pumped a bit more refrigerant into it and ran the high side pressure up to about 250 which seems to me to be quite high for a 70 degree day. Anyway the nozzle temp started coming down. The other day it was in the 90's which would run the high side pressures up particularly at slow speeds with the hood closed. When the car starts moving and forcing more air across the condensors the high side would come down.

Is it possible that I have the wrong size orifice in this thing not allowing proper refrigerant flow? Given the description of the system would you have a recommendation for an orifice? Back in another lifetime when I actually did this for a living I made a couple of hose clamps which I can clamp the hoses shut and change an orifice in about 5 minutes without discharging and recharging the system.

The more I think about it the more sense it makes.
71403
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Re: strange cooling

Postby 71403 » Sun Jun 24, 2018 11:21 pm

Gauges will tell the story on yours but have seen similar in my own "mixed parts" system. Best I can figure if high side pressure is too low (low charge or condenser "overcooled") there's not enough pressure to push enough refrigerant past the fixed oriface to properly fill the evaporator.

Didn't believe it until I added thermocouples on the evap inlet/outet and drove around a bit could watch superheat rise when the high side pressure drops.
grumpy old man
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Re: strange cooling

Postby grumpy old man » Mon Jun 25, 2018 7:51 am

My problem seems to be some kind of restriction upstream of the evaporator so that it is taking too much pressure to fill the evaporator. 250 psi on the high side to get the thing to even cool on a 70 degree day is way out of reason. And by cool I mean barely 40 degrees at the nozzle, the accumulator is not sweating at those gauge readings. The logical place to look for a restriction is the orifice and just because it is new does not mean it is good. The thing that triggered it in my mind was that as I was watching the gauges with the engine running at about 1500 rpm the low side was short cycling like it would with a low charge but the high side pressures were saying overcharge. I have been away from this for too many years to make a reasonable guess what size orifice I might need. Maybe I should just go to the Ford counter and get the factory orifice for a 97 Crown Vic and give it a go. The one that is presently in there is from the local Autozone so who knows what that is. What do you think?

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