MG Sports Cars

I have the underdash air-conditioning unit that came originally on my 77 MGB. I was wondering if you all had part numbers for a small AC compressor and condenser that would work well. I have a wholesale account with O'Reillys and i can get the parts fairly cheap. And the hoses I can crimp myself I have a hydraulic crimper I picked up a swap meet and I have a local air-conditioning supply I can buy all the fittings from.

Dave

I believe the Sanden 508 is the compressor you want.

I matched the condensor to the radiator space available.

It seems that the size of the condenser has more to do with how well the system cools than any other factor. (This wisdom gleaned from trucking where a very similar compressor is used to cool a living-room sized cabin and multiple evaporators are in play. With the change to r134 the condensers got larger and the rest of the system stayed the same.) Condenser area seems to be the key. But does anyone know of a vendor who sells generic condensers by size?

Jim

The ebay store, Coldmaster, Inc., is where I bought my compressor. You might try looking there. It was just on ebay though, I don't think they have a website.

Off the top of my head two company's have online catalogs with pictures and dimensions.
I use"the cooling depot" all the time and "4 seasons" as a 2nd call.
In the States 4 seasons is probably a better bet.
Cheers
Fred

I got my condensor from Nostaligic Air, ordered from their stock to my spec.

[www.nostalgicairparts.com]

Give them a call for tech advise.



Edited 1 time(s). Last edit at 02/02/2012 02:50PM by mowog1.

A condenser page from Nostalgic Air....
[www.nostalgicairparts.com]

vintage air and old air

R-134A system has many variables from its predecessor, freon R-12. Jim is right in mentioning the condenser as the main change done. The modern system has a teflon liner inside the rubber hoses to ensure better rubber containment of the freon. The compressor uses R-134A compatible seals and O-rings, the orifice tube or expansion valve is sized differently. There's also three design types of the condenser used for R-134A; one design being of much superior efficiency than the other two.

The lubrication oil is also formulated better; it either uses PAG oil or Ester oil. It's good to respect the manufacturer recommended oil viscosity for proper lubrication although some aftermarket "Universal" oil are available. Its BTU heat exchange also happens at different pressure than R-12.

I have done many conversion from R-12 to R-134A and many conversion were a disaster. The best result was done while using a specific conversion gas called "Freeze-12". Both conversion have to be done with partial charge to cool properly.

Considering the small area on a MG, I would buy the high-efficiency model offered by the suppliers mentioned above. The compressor is size proportionally to the cubic area it has to cool making a convertible act like a large car; it is also only as good as the condenser permits it to be.

If you can't afford new components, then look into junk/wreck yards, you'll find some original equipment made by Sanden and also some compact R-134A condensers that could fit the MG front area; just make sure you flush it out real good with A/C flush. I would start with a clean system and add the recommended oil for each components to ensure not over oiling the system as it will cut down on cooling and raise head pressures.......

My 2 cents

Jacques, could you elaborate on the preferred (most efficient) condenser design?

On my car I am not limited by frontal area (radiator is 17 x 30") but the units in Rick and Graham's links above are narrower and would partially block the radiator with the end supports. It will be a couple weeks before I am ready to buy but if I can't find a matching off the shelf unit I should probably look for a supplier that can provide custom sizes. Something like 15 x 28 overall would probably be a good size to look for.

I am of the opinion that the A/C in a convertible should be able to cool the entire world, but since that is not physically possible I'll settle for the max I can get in the space I have.

Jim

Jim, air conditioning technology has emerged like everything else in automotive world. The most efficient A/C condenser being the "parallel" design sadly has to be replaced if you ever have (in A/C term) a "Black Death" failure. I have tried to flush many high efficiency modern R-134A condenser with no success. Running close second, is the R-134A modified "Serpentine" design. The best thing someone can ever install to their A/C system are traps in both, suction and pressure side; that should be consider buying an insurance policy to protect every components.

I've installed many custom R-12 A/C system in the old days from salvage yard components with great success but that was then with the much more efficient R-12, however, the fundamentals of automotive air conditioning are still the same: 970 BTU (British Thermal Unit) absorbed at evaporation time in the evaporator and carried out to the front heat exchanger (condenser) to be liquified and back to the metering arrangement (valve or orifice tube).

You are right in wanting to use the largest condenser as possible but lets not forget that the evaporator is also what removes the heat out of the car, hence, try using one as physically large (thick) as possible. Small evaporators have to use smaller CFM blower fans and do a poor job especially in a convertible. There's also lots of trick stuff modern A/C systems have such as "engine overheat A/C cut-out", "wide open throttle cut-out" and etc,...

Here's a couple of interesting links with some advice; I hope it helps you in a proficient built on your A/C......

[www.e38.org]
[www.streetrodderweb.com]
[imageshack.us] (photos of condenser design)

Jacques

So the condenser Rick used is a parallel design. Pretty reasonable on the price. I guess I'll call them and see how close they can get. There is a VW evaporator I'm considering that is quite a large volume. It will mean a redesign of the dashboard but that is something I've been thinking about anyway, and using the area behind the dash as a plenum for A/C distribution instead of messing with ductwork. Very interesting comment about using a thick evap core. I hadn't really considered that aspect but it makes good sense. (The VW core is very thick) Adequate airflow will not be a problem with the big 3 speed blower I have on the heater now. It's out of an International Travelall.

Thanks for the info, That helps.

Jim

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Dave, I think our West Coast Distributor installed air in his "B" and he had a 60V6. His name is Andy Bradley and his website should be [bradleyrestoration.com]

Perhaps he might give you some idea of what you might be able to do if he has done the installation.

Dann Wade
British Car Conversions



Edited 3 time(s). Last edit at 02/21/2012 10:42PM by kill r b.

I waited too long to get the napdeal but the condensers and drier are ordered. Black, 16 x 25". But I have to say, the help from their tech support guy was grudging. There was a reason for it and I don't think it would be any different with any other reputable company, but it still didn't sit all that well. He did not want me sizing my system based on the available condenser area, but on the evaporator size. Along the way he let it slip that there was a 2:3 ratio but naturally enough when I followed up and asked if that was based on volume he said no, it was based on BTUs. Which of course depends on things like fan speed, temperature drop, ducting restrictions and a whole lot of other stuff that is fixed if you buy one of their evaporator units but is infinitely tunable if you build your own. I understand where he was coming from. He wanted me to start with one of their evaporator units and go from there. But it wasn't helping my cause, and there was no way he was going to help me design my own evaporator. But the bottom line is, I managed to get what I wanted to begin with, along with some other critical information. (the evaporator/condenser ratio) The price was quite reasonable, the call was a success, and I now have what I need in terms of info to design the inside unit to work well. Considering that the condenser is the limiting factor in overall heat exchange, I simply have to match volume and make sure I can get adequate airflow through the evap. It'll be a big 'un but I am planning for that.

The second condenser will run the intercooler system and will be in front of the A/C unit. This makes the overall stack about 4" thick which is really about the limit of what is usable in terms of airflow. However, that will be offset somewhat by the large area with over 400 sq. in. The IC will not normally be operating at the same time as the A/C and vice versa which will also help, although I suppose they could.

Jim

OK, that ratio obviously does not hold true on volume. I'm seeing some systems where the ratio is reasonably close (early GM) and some where it is totally upside down (late VW). The calculated volume of the evap should be about 250 cu.in and early GM units fall in that range. A late '80 VW otoh has 536 cu.in. which exceeds the same ratio run in reverse IF it had the 15 x 25.5 condenser core size which is doubtful. To hold the ratio it would need over 800 cu. in. of volume in the condenser, which is ridiculous. The clear indication is that the GM used a HVAC fan which sent a tornado through the core and the VW provided more of a gentle breeze. From this example it appears to me that it is not possible to oversize the condenser if the evaporator is not severely cramped for space. The tech guy made some reference to the compressor not being able to get enough refrigerant to send to the evaporator if the condenser was too big. What he was saying essentially is that all of the refrigerant gets pumped into the condenser and is held there waiting to be expanded in the evaporator while the compressor is sucking the return line dry. In that case wouldn't you just add refrigerant to bring the low side pressure into spec? Or let's say it's a cool day and the fan is on low. The same thing would happen with any expansion valve system would it not? The compressor would continue to pump until it could pump no more. Far better to stack all the freon up in the condenser and starve the compressor (how is this a problem?) than to blow a hose or gasket on the high side because the condenser filled up. And if this is really a problem, how is it that semi systems with a VERY massive condenser work very well? Never run the system unless it's hot out maybe? Don't think so, there is no faster way to defog the windshield.

OK, I get that too much A/C can be a bad thing. How often is that going to happen with a convertible V8 MGB? Ever? Maybe Never? I think I can live with that. They say that about home systems too. I oversized ours probably 1/2 to 1 ton and couldn't be happier.

The VW evaporator is 26" x 5-1/2" x 3-3/4" which is much larger than the average. What happens with an oversize evaporator? The ductwork and blower can be less efficient and still do the job. Seems like that describes the MGB system pretty well. With a new dashboard design, I think there is room to put it behind the dash, block off the bottom and use the enclosed space as a plenum. Still some work to do on the blower and heater but I'm looking for a way to use the stock heater box, or at least the ducting, along with a big blower like the one I have now. But for the time being I will get the other system pieces in place and do that part in a later stage. Maybe by then that speedo I want will be available.

Jim



Edited 3 time(s). Last edit at 03/29/2012 10:43AM by BlownMGB-V8.

Turns out the VW unit is for a Vanagon (pop top micro-bus camper). The condenser for that is 19 x 17 x 1" or 323 cubic inches. The 2/3 ratio run backwards is 484, still shy of the 536 sq inches of the matching evaporator, AND the Vanagon comes with a second, rear mounted evaporator.

The vanagon evap is really much too large to fit behind the MG dashboard even if it is moved out. It would have to go all the way out to the steering wheel. But something in the 300 sq in range should function nicely. So the trick is to find that in a package layout that is useful. So maybe something like 5" x 2" x 20" which is still big but much more manageable. Or 4 x 3 x 25. A thicker core has more time to cool the air and gives a better temperature drop, but slows airflow, requiring a larger fan or more cross section. So basically, move the dash out 2-3 inches and duct the air through it vertically. Always helps to know what you're looking for.

Jim



Edited 1 time(s). Last edit at 03/29/2012 02:09PM by BlownMGB-V8.

Quote:

Considering that the condenser is the limiting factor in overall heat exchange

Don’t forget, unless you have an engine driven fan, you’ll need to switch on the electric cooling fan(s) when the A/C system is operational....and, of course, the performance of the condenser in rejecting heat depends on the fan performance.

Quite right Graham. I have the same Camaro fans we put on the MG-Roadmaster, I think they will be adequate. If I want I can even use the Saab 2 stage temp switch I used on the TR-7 and stage them for engine coolant. Probably should switch both on for A/C and WOT.

Jim

If I recall my truck design days, there was a pressure switch in the evap box line that sensed when the system was "pressurized/operational' and kicked on the fan circuit.