Summer plug for Rennair's Pro Cooler.

[mthomas58]

It's a 72 degree morning here in Atlanta with 95% humidity after heavy rains yesterday. While filling up I noticed condensation on the fender from the icy cold Rennaire Pro Cooler behind it. Never noticed that before. Vent temps in the high 20's on the way in with the A/C temp knob fully cranked (can't resist) . Just sayin!

A/C Mods:

Barrier Hoses
Pro-Cooler
Griffiths Serp Dual Rear Fender Condensers (2) fan assisted
Griffiths Front Serp Condenser
Griffith's next generation front condenser is 75% thicker.
3 fans mounted to rear stock condenser above engine
Adding 3 fans to rear A/C condenser
Griffiths upgraded Wirblesturm Evap blower motor
Anyone here with a 1986+ done a Kuehl Wirblesturm "Hurricane" evap motor upgrade?
Griffiths variable speed fan controller
Re-routing of bowtie vent to evap intake opening "DIY Recirculate" & vent temp guage addition (colder in equals colder out)
How do you monitor the performance of your A/C system? Clock / VDO Temp Gauge Swap.
New idea to help lower A/C vent temps.

[Kemo]

I had a pro-cooler in my last 911 here in central Texas and thought it did a great job. i had the serpentine evaporator installed along with new barrier hoses and procooler dryer. It made a huge difference at the vents. The only other obstacle was getting more air to come out of those ity bitty vents i my SC. I should have kept that car

[Josh D]

You run your A/C when it's 72* outside? Seriously?

[SilberUrS6]

Originally Posted by Josh D

You run your A/C when it's 72* outside? Seriously?

Funny thing - 72 at 95% humidity feels pretty warm. Nice thing about AC is the fact that it reduces the cabin humidity. Even at a low AC setting, improving the humidity in the cabin is a nice thing.

"It's not the heat, it's the humidity."

[wwest]

Originally Posted by mthomas58

It's a 72 degree morning here in Atlanta with 95% humidity after heavy rains yesterday. While filling up I noticed condensation on the fender from the icy cold Rennaire Pro Cooler behind it. Never noticed that before. Vent temps in the high 20's on the way in with the A/C temp knob fully cranked (can't resist) . Just sayin!

A/C Mods:

Barrier Hoses
Pro-Cooler
Griffiths Serp Dual Rear Fender Condensers (2) fan assisted
Griffiths Front Serp Condenser
Griffith's next generation front condenser is 75% thicker.
3 fans mounted to rear stock condenser above engine
Adding 3 fans to rear A/C condenser

If your Pro-cooler is CHILLING the fender at that range/distance then something is very, VERY wrong. Cooling, CHILLING any component other than the evaporator has to be a serious flaw, design or some failure case.

Griffiths upgraded Wirblesturm Evap blower motor
Anyone here with a 1986+ done a Kuehl Wirblesturm "Hurricane" evap motor upgrade?
Griffiths variable speed fan controller
Re-routing of bowtie vent to evap intake opening "DIY Recirculate" & vent temp guage addition (colder in equals colder out)
How do you monitor the performance of your A/C system? Clock / VDO Temp Gauge Swap.
New idea to help lower A/C vent temps.

~50F vent temps would probably suffice for dehumidification down to human comfort level, ~40%, in that climate, 95% Rh, 72F.

[Kemo]

i think the dryer is supposed to get cold as its Jacketed in "un-expanded" freon from the evaporator. mine got pretty cold

[mthomas58]

Originally Posted by wwest

~50F vent temps would probably suffice for dehumidification down to human comfort level, ~40%, in that climate, 95% Rh, 72F.

Correct, unless ambient temps are extreme, I normally run the A/C temp range from 2:00 o'clock to 4:00 o'clock giving me vent temps in the 38 to 45 degree range. Plenty comfortable and provides frequent compressor cycling to avoid extended running & freezing at high Rh conditions.

[sennasixty8]

Your car runs on diesel?

Out west, our handles are green jacketed for the oil burners... =)

[Josh D]

Your car runs on diesel?



=)

Yours doesn't? ; )

[mthomas58]

Originally Posted by sennasixty8

Your car runs on diesel?

Out west, our handles are green jacketed for the oil burners... =)

BP Station - all the handles are green.

[McconnellSilva]

Nice thing about AC is the fact that it reduces the cabin humidity.

[mthomas58]

Originally Posted by wwest

~50F vent temps would probably suffice for dehumidification down to human comfort level, ~40%, in that climate, 95% Rh, 72F.

If your Pro-cooler is CHILLING the fender at that range/distance then something is very, VERY wrong. Cooling, CHILLING any component other than the evaporator has to be a serious flaw, design or some failure case.

Wwest, something is not VERY wrong, The Pro Cooler uses spent refrigerant from the Evaporator en route back to the compressor to pre-chill the refrigerant entering the expansion valve/evaporator. It is not at all unusual for the exterior canister of the Pro Cooler to have ice on it.

[billybek]

Originally Posted by mthomas58

Wwest, something is not VERY wrong, The Pro Cooler uses spent refrigerant from the Evaporator en route back to the compressor to pre-chill the refrigerant entering the expansion valve/evaporator. It is not at all unusual for the exterior canister of the Pro Cooler to have ice on it.

Your right. It is a suction gas to high pressure liquid heat exchanger. By further sub cooling the liquid refrigerant before the expansion valve, you can extend the net refrigerating effect to produce more cooling.
The down side to this is that the refrigerant returning to the compressor is superheated more. Not really smoke and mirrors, it can be effective but you will have more heat to reject.
Looks like you put a lot of time and effort into getting Porsche's version of a piping screen saver to produce some real cooling. You guys really need it down there!

[wwest]

Originally Posted by mthomas58

Wwest, something is not VERY wrong, The Pro Cooler uses spent refrigerant from the Evaporator en route back to the compressor to pre-chill the refrigerant entering the expansion valve/evaporator. It is not at all unusual for the exterior canister of the Pro Cooler to have ice on it.

Sorry, but I stand by my position.

Chilling of the liquid refrigerant in this way is not a bad idea, but chilling the fender well/fender area..? In order for that to happen to much refrigerant cooling capacity is getting through the evaporator.

My guess is that the system is set for maximum cooling but minimum blower speed. COLD, discomforting system airflow even with the blower at minimum.

My first instinct was to advise that the procooler be somehow insulated in order to prevent such a high loss/waste in cooling capacity. But in this case that would likely result in slugging, destruction of the A/C compressor.

[Jim Sims]

The subcoolers (suction line heat exchangers) I have adapted and installed in 911 A/C systems have a geometry that places the warm, high pressure liquid refrigerant on the outside of the heat exchanger and the excess cold expanded gas/liquid from the evaporator on the inside. To further improve thermal efficiency I wrapped the outside shell of the exchanger with "Prestite" type (cork/asphalt) flexible tape insulation wrapped with aluminum tape. I used these insulating materials given the installed location above the front splash pan that exposes the subcooler to wet conditions at times. The suction line heat exchanger type subcoolers can measurably aid the "real-world" net performance of R-134a A/C systems especially under marginal conditions of reduced condenser performance or low refrigerant charge. There are technical papers available with the results of systematic investigations of this topic. I note that Delphi is now manufacturing and marketing a suction line heat exchanger subcooler for OEM A/C automotive applications. The suction line heat exchanger subcoolers work best in a counter flow arrangement and with a geometry that minimizes pressure drop on the suction side (low pressure line between the evaporator and compressor). The suction line heat exchangers for subcooling available from Doucette Industries also incorporate a corrugated wall between the hot and cold chambers; this promotes turbulence to improve heat transfer and provides pockets (if mounted horizontally) on the cold side to retain cold, liquid refrigerant to allow it to evaporate in the heat exchanger to provide additional cooling effect due to the phase change.

I have run one of these suction line heat exchanger subcoolers in my '76 for about nine years now and it is still performing well. Given my location and service cycle I get very good performance with a single deck lid condenser (engine fan air flow), aluminum high pressure refrigerant line tubing and a subcooler. I will be building another subcooler in the near future (hopefully with o-ring type fittings) for a friend to use in the upgrade/refurbishment of his factory Carerra A/C system.

See below for a link to subcooler information.

Jim


A/C Subcooler Information

[billybek]

It was 95% RH, doesn't take much temperature change until you start to condense moisture on cold surfaces. With 29 degree leaving air, his refrigerant temp would be around 20 deg F. Some of that moisture could have been ice melting out from under the insulation.
It might be tempting to overfeed the evaporator with refrigerant to give the subcooler more cold refrigerant to work with. Lowering the temperature of the leaving gas from the evaporator at a given pressure just means that you are not changing the state of the refrigerant from liquid to vapor. That is where the ability to absorb heat comes from. Reducing the superheat leaving the evaporator doesn't result in an increase in cooling performance.
There are some downsides using one of these. More superheat in the suction gas to the compressor. This results in a higher specific volume of suction gas, higher discharge temperatures and higher compressor operating temperatures.
The OP has made improvements to the condensing side of the system to allow for this. Properly set up the pro cooler could be an asset to the system but you don't get nothing for nothing and damn little for free in refrigeration.

[Barrpete]

Originally Posted by billybek

It was 95% RH, doesn't take much temperature change until you start to condense moisture on cold surfaces. With 29 degree leaving air, his refrigerant temp would be around 20 deg F.

At the stated ambient conditions 72F and 95% RH the dewpoint is 70F. Wouldn't take much at all to drop the surface temp of the fender 2 degrees.

[Jim Sims]

Originally Posted by billybek

It was 95% RH, doesn't take much temperature change until you start to condense moisture on cold surfaces. With 29 degree leaving air, his refrigerant temp would be around 20 deg F. Some of that moisture could have been ice melting out from under the insulation.
It might be tempting to overfeed the evaporator with refrigerant to give the subcooler more cold refrigerant to work with. Lowering the temperature of the leaving gas from the evaporator at a given pressure just means that you are not changing the state of the refrigerant from liquid to vapor. That is where the ability to absorb heat comes from. Reducing the superheat leaving the evaporator doesn't result in an increase in cooling performance.
There are some downsides using one of these. More superheat in the suction gas to the compressor. This results in a higher specific volume of suction gas, higher discharge temperatures and higher compressor operating temperatures.
The OP has made improvements to the condensing side of the system to allow for this. Properly set up the pro cooler could be an asset to the system but you don't get nothing for nothing and damn little for free in refrigeration.

Au contraire:

One gains 5 to 10% in COP and capacity with a suction line heat exchanger subcooler in an "real world" automotive R-134a system; perhaps even more with a 911 system.

See:

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1493&context=iracc&sei-redir=1&referer=http%3A%2F%2Fwww.google.com%2Furl%3Fsa%3Dt %26rct%3Dj%26q%3Dincreasing%2520capacity%2520with% 2520suction%2520line%2520heat%26source%3Dweb%26cd% 3D1%26sqi%3D2%26ved%3D0CEwQFjAA%26url%3Dhttp%253A% 252F%252Fdocs.lib.purdue.edu%252Fcgi%252Fviewconte nt.cgi%253Farticle%253D1493%2526context%253Diracc% 26ei%3Dqq7bT7CiDqfN6QGkiaWrCw%26usg%3DAFQjCNEeitqy svEsqVNJqQOmuQag1yBVVw#search=%22increasing%20capa city%20suction%20line%20heat%22

[billybek]

Originally Posted by Jim Sims

Au contraire:

One gains 5 to 10% in COP and capacity with a suction line heat exchanger subcooler in an "real world" automotive R-134a system; perhaps even more with a 911 system.

See:

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1493&context=iracc&sei-redir=1&referer=http%3A%2F%2Fwww.google.com%2Furl%3Fsa%3Dt %26rct%3Dj%26q%3Dincreasing%2520capacity%2520with% 2520suction%2520line%2520heat%26source%3Dweb%26cd% 3D1%26sqi%3D2%26ved%3D0CEwQFjAA%26url%3Dhttp%253A% 252F%252Fdocs.lib.purdue.edu%252Fcgi%252Fviewconte nt.cgi%253Farticle%253D1493%2526context%253Diracc% 26ei%3Dqq7bT7CiDqfN6QGkiaWrCw%26usg%3DAFQjCNEeitqy svEsqVNJqQOmuQag1yBVVw#search=%22increasing%20capa city%20suction%20line%20heat%22

Like I had mentioned twice before, suction line heat exchangers can be effective.
The system must be set up properly for them to work.
Being short on the ability to condense at the best of times, pre 964 cars could benefit from a pro cooler if properly equipped.
But it isn't magic and it isn't free. Performing cooling outside the evaporator isn't useful cooling. Further sub cooling HP liquid refrigerant before the metering device does increase the net refrigerating effect in the evaporator. It does this by reducing the amount of flash gas after the metering device. More liquid to boil off in the evaporator = higher net refrigerating effect (Btu/lb of refrigerant).

[wwest]

"..suction line heat exchangers can be effective..."

Can be.....but not when so much of the refrigerant's cooling capacity is being WASTED for atmospheric cooling.

"..More liquid to boil off in the evaporator..."

Not the way I see it. Pre-chill the liquid refrigerant = SLOWER boil off. Pre-chill the refrigerant and the evaporator throttling system will close the expansion valve moreso, the evaporator reaches the "target" temperature much sooner.

As I said, my bet is that the system is set for MAXIMUM cooling, but with the lowest blower speed. Other than being wastefull there is a strong possibility of compressor slugging.