TECH TALK - Page 11
AIR CONDITIONING YOUR B-GT, C-GT, OR B- GTV8.
As we are all getting older and drive our normal cars with very efficient air-conditioning it becomes ever less pleasant, particularly during summer, to drive an English Hot Box where even fresh air inlets used to be optional in early cars, [The under dash fresh air door], after 72, the centre console and centre dash fresh air vents were standard.
2 years ago I completed the A/C of my C-GT [June 06.] this totally transformed an excessively hot and noisy car into a proper GT car. We can use the audio system and go anywhere in great comfort any time of year, whatever the outside temperature is, hot or cold, and indeed use the A/C all year round as with the low sun angle during winter the car still gets warm to hot.
Window tinting is essential because of the low Winter Sun angle and direct radiation thru the side windows, a tinted and banded windscreen is useful if you have to replace a windscreen. 25% tinting is legal in Queensland for windscreens and 35% for the other glass.
I am not going to write a “Tech Talk” detailed article on the project but an overview of what A/C entails, parts, costs, practical considerations etc.
There are several items to be installed, Evaporator [the unit in the cabin], Condensers 2 for the “C” & “V8”, 1 for the “B”, Compressor, Receiver/Dryer, Relays, Fuses, Much Bigger Alternator, and for completeness throttle compensation and a way to not allow the system to run until the engine is running. This is how modern cars work where the A/C is left on all the time and the system comes up under engine management control.
Now the nasty part: COST, with insulation which is essential in both the “B” & “C” if the A/C is not to fight the engine and exhaust heat. They were designed as basic Sports Cars and not as Saloons. With all components, brackets and fittings the whole bloody shooting match will cost about $4,000, if you do most of the work yourself other than the A/C plumbing and gassing of the system. Having the job done by others is not a practical option as the cost will be a high percentage of the value of the car in most cases.
The actual A/C is the easy part, what is tedious and very time consuming is installing the insulation and this will depend to what extent you want to go to achieve quietness & coolness, as in a current A/C car. I took about 7 months total, a mixture of full time and part time work, with days of up to 6 hours with the insulation.
I tend to be very old fashioned and believe in the ancient adage of “If a jobs worth doing it’s worth doing properly”. So I probably have overdone it [being me]. In retirement I took this on as a very interesting project, and it was, it actually took me back to training school days and to relearning all the old skills. This 40 year old “Pretty Fast Truck” [PFT-000] has now become a most interesting hobby, as well as a very enjoyable GT car, the way it should have been in the first bloody place.
While I was doing the A/C another “C-GT” owner was following me along on a “Monkey see, Monkey do” basis and he spent a lot less time doing his car, but didn’t go to nearly the same extent with the insulation. A different type of insulation could cut the time by months if only heat insulation is required. I went for a Thermal and Acoustic approach.
In our “C” we have about the same conditions as in our BMW 325i Coupe, as regards coolness and a quiet cabin below 90 Kph. We can listen to classical and jazz music as long as we are doing 100 Kph or less, above this speed the wind noise dominates and we can do nothing about that. Ancient thinking and design dominate.
All the components are from the “JAY AIR Automotive Air Conditioning Catalogue”. Don’t bother to even think of parts from the wreckers as it is a total false economy. A/C parts have to be new and clean with no corrosion, moisture or wear to get long term reliable service.
The component parts and model numbers are as follows:
2 250mm by 250mm by 30mm, Condensers. Part # CN5042.
2 Pusher Fans 225mm. [6.8 Amps each].
Part # EF3527.
1 Evaporator. [mounted under glove box]. Part # EV1401.
1 Soft Start Vane Compressor, Seiko Seiki.
Part # PM3111.
1 Receiver/Dryer and Binary pressure switch. Common Part.
2 Eyeball Vents.
Part # LV0478.
1 65 Amp Alternator. The A/C system draws up to 29 Amps.
1 Vacuum Motor and Solenoid Vacuum switch.
1 Oil Pressure switch. Normally off, on with oil pressure.
2 30 Amp relays. use “Bosch” as they are reliable.
1 Lucas copy fuse box, similar to the existing fuse box.
For cars without a centre console as fitted to 72/73 cars you need to get the centre console [2 components], 2 dash fresh air vents, which are all now available. The vents fit into the place where the Radio normally mounts. The Radio now lives in the centre console.
In the “C” and “V8” there is either no space and or too much heat to mount a single condenser in the engine bay. These cars do not need any more heat or obstruction to the radiator air flow. With an MGB- GT a single condenser can be fitted in front of the radiator as there is lots of space and engine conditions will tolerate mounting in the engine bay.
For the “C” and “V8” two condensers are used, these mount in the wings below the headlight bowl, there is space with either the standard valence or the later air dam so the external appearance is not affected. Slots are cut in the valence to give plenty of air to the fans and unload the fan motors at cruise. In our car we discovered that they also give brake cooling which is a great benefit.
Inside the cabin the Map Pocket has to be removed to allow the Evaporator to mount as it is a very nice fit between the centre trim and outside trim. In our car we have mounted the Map Pocket on the vertical panel under the “Kiddy” seat, central behind the passenger seat. This allows the driver to actually get things out of the pocket while in a seat belt. The “dopey” bloody poms never thought of this. In the case of the “C” they seemed to NOT consider lots of things. To operate the fresh air door [behind the centre metalwork] I added a push-pull rod and a bracket next to the console so the driver can operate the fresh air door while driving the car. You have to do this otherwise you cannot operate the fresh air door as the feed tubes to the centre and right hand side block access to the operating lever.
In the “C” the windscreen washer container moved up next to the heater between the heater and brake booster, the windscreen washer motor [Part # GWW125] mounts inside an opening in the inner wing, along with the solenoid/vacuum switch. A 2 litre food container becomes the new washer bottle [original one is 1.75 litres].
The radiator overflow tank moves to where the windscreen washer container was. The relays and additional fuse box mount over near where the fuse box is fitted.
In our “C” the compressor mounts onto the timing cover and block and takes the space where the overflow tank was, the threaded mounting holes are already in the block as are the holes in the timing cover. A Japanese pulley is mounted onto the harmonic balancer, to suit the compressor pulley, on our car the drive pulley to compressor pulley is 1.23:1 step up as the “C” idles @ about 800 RPM.
For the MGB-GT and MGB-GT V8 you will have to sort these mountings out yourself as well as how to mount the compressor and it’s driving pulley. The compressor has a double pulley so it could be used as an idler/transfer pulley to drive the alternator from the compressor. I would look to see how to drive the compressor from the crankshaft rather than use the transfer idea. The commercially air-conditioned MGB-GT’s mounted the compressor where the alternator was and then drove the alternator, mounted above the compressor, with a separate belt from the compressor pulley.
I started with a 43 Amp alternator which worked fine but was limited in traffic with A/C, Lights [100/55 Watt Halogen], and Radio. The “C” and “V8” run at such low revs in traffic that 43 Amps was on the low side. The 65Amp unit will handle everything from idle. I changed the alternator pulley ratio from 1.875:1 to 2.1:1 at the same time, as our car will run happily @ 1,000 RPM in top and 1,100 RPM in O/D, the “V8” will be similar.
Mounting of the Receiver/Dryer can be almost anywhere in the line from the condensers to the Evaporator, in our car it goes behind the radiator mounting panel on the left side, just in front of the compressor drive pulley. There is not much spare space in the engine bay now. I can, and have, removed the engine and transmission with the A/C system intact by tying the compressor over to the inner wing. I was very pleased that this was possible. Murphy’s Law almost guaranteed that I would have to do this and indeed the rear crankshaft seal failed not long after the A/C system was finished.
While I had the engine and transmission out I insulated the firewall on the engine side as well as the inside of the tunnel [this is where most of the heat in the cabin comes from]. Cars with a sun roof seem to be a lot cooler as they can let this built up heat out. Our car is now cool everywhere even the chrome ring around the gearlever stays only warm and not very hot as from the factory, the tunnel ,foot-wells and floor are all comfortable even after a 300 mile day run in summer. In winter we leave the A/C on the least cool setting and add fresh air via the heater [off side] door in the left foot well. The fresh air door can be opened to the 1’st and 2’nd positions as required. Position 3, is not possible as the A/C feed tubes will not allow this, and if the air door is opened to the 3rd position it will direct air & dust directly into the top of the radio. Stick to position 1 & 2 only.
I am happy and willing to talk to club members and to show what is required on an individual basis, car by car, as this detailed knowledge cannot be successfully documented. 1 picture is worth a 1,000 words and there are lots of photos in my A/C files. Members who would like to see the photos, to get a feel for the work required, are most welcome to contact me re a suitable time and date. If you intend to keep your car for some years this is a most worthwhile thing to do, the difference is amazing, cool and quiet. I think, but don’t know, that we have added about 30 to 35 Kilos to the car, all down low and in the centre which in the “C’s” case is more of a benefit than a disadvantage. A/C reduces consumption by only 1 or 2 MPG overall.
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