Improved Ac

INCREASE AIR FLOW

This simple, no cost, modification will substantially increases the air volume/flow (CFM) through the cockpit vents. Although the temperature remains the same, the increased air velocity make it feel much cooler. On the footwell firewall , covering the recirculation air intakes, are aluminum blanking panels that can be removed, thereby increasing, dramatically, the volume of air that enters the system. The driver’s side intake is totally blocked & removal necessitates drilling out the 4 pop rivets that secure the panel. The passenger side panel, which only partially blocks the intake, is held on by 2 rivets. Caution; a) If the nose air intakes are not sealed (see below), removal of these panels may create a back-draft trough the footwell intakes when either the A/C or heater is turned off, which is the reason Lotus installed them. A solution is to use “Velcro” on the removed panels to enable temporary installation when needed. b) As a precaution against the drilled out rivets falling into the ducting on the other side of the bulkhead, do not drill out the complete head of the rivet. Only remove enough of the head to pull the panel off and then apply a little glue or silicone caulk to retain the remaining rivet. COCKPIT VENT AIRFLOW ................RECIRC. OFF................RECIRC. ON .................................................. ....(Outside vents open)...........(Outside vents closed)

Footwell vent closed (normal)----------27mV........................16mV Footwell vent open (modified)----------50mV .......................45mV There is a greater airflow at the vents with the outside air intakes open, but that air, in the A/C mode, is warm, unconditioned and could result in a higher cockpit vent temperature.Note – Higher voltage (mV) equals greater air flow Credit to "Insane" for above test

SEALING FRONT AIR INTAKES - USE ONLY RECIRCULATED (CONDITIONED) AIR

To better understand the HVAC system it would be better to describe the “recirculation” switch as “shut off outside air switch”. Air is always being drawn from within the vehicle (recirculated). When the recirculation switch it pressed on, it activates a flap valve that closes off the outside air that is drawn in from the nose air intakes. It has been noted that this flap valve has a tendency to leak, thereby introducing unwanted warmer (A/C mode) or cooler (heater mode) into the system. A very simple modification is to tape over the two air intakes (see below photo) in the nose of the car using duct tape. There is a possibility that outside air could still enter the system though gaps in the heater / AC box. Credit to "ZAMMY1"

WINDOW FILMS (TINTING) - REDUCES HEAT LOAD ON A/C

Reducing the solar energy through the glass areas has a substantial effect on reducing the cockpit temperature that the A/C has to cool. The latest, and arguably the best film is Crystalline Window Film which has the distinct advantage of having a clear version that could be used on the windshield (check local laws). Because of its technology, "Crystalline", being unlike other films, stops more solar heat, even in its clear version. Note; clear in vehicle glass terms is 70% light transmittal. I used "Crystalline" on both door windows, the windshield and the rear window and saw a temperature reduction on top of the dash, typically, of approximately 30’F

INSULATING THE SIDE SILLS & FRONT FIREWALL - REDUCES HEAT LOAD ON A/C

Routed inside the side sills are the coolant, heater & oil cooler pipes which have the effect of heating the sills, which then act like radiators. Insulating the exterior surface of the sills, on the interior of the car, reduces the interior temperature, enabling the A/C to better cool the cockpit. I used Thermowell Duct Insulation available from either “Lowes” or “The Home Depot” in a 12”W x 15’L x 1/8” thick, self adhesive roll to completely cover the sills. I removed the lower section of carpet and aluminum trim strip by drilling out the rivets (caution, see item 2 above), additionally, I removed the plastic cover that sits on the top of the sills. After the top and side of the sills were insulated I then re-trimmed them, utilizing a pattern I had made, with a micro fiber material that I purchased from a local fabric store. I also insulated the front firewall around the recirculation intakes as much as was possible. The sills are now 20’F cooler.

HEAT SOAK - CAUSES THE CONDITIONED, COOLED AIR, TO INCREASE IN TEMPERATURE (Also the reason warm air flows through the vents when the heater and A/C are turned off) During the first few miles of driving, I noted that the A/C vent temperatures dipped to their minimum, as low as 40’f approx, with ambient in the 70's, and then slowly rose over the next 10 -15 miles of driving to approximately 52’f, where they stabilized. I believed that there could only be three reasons for this rise, all heat soak related; ....a) Heater system ....b) Cooling system ....c) Solar energy I then noted that this temperature rise happened even if the heater feed hose was clamped off and it was a cloudy day. Alternatively, if the car was sitting in the sun for a prolonged period, the vent temperature still dipped to it's usual low point. This ruled out the heater matrix or solar energy being the cause of the heat soak. My conclusion, therefore, was that the heat soak was caused by the only item left, the cooling system, and to remedy it, here is what I did; 1) There is a hood, center spline insulation block, that appears intended to reduce the heat transfer into the HVAC system. The problem is that there is a large gap in the base of this block that allows heated air from the radiators to leak though, which increases temperatures in the HVAC system. To counter this I applied the same insulation that I had used on the side sills across the opening in the hood center spline.(Credit to "Doug Porsche" for this find)

2) There are 2 radiator cowl components, left & right, the inside face of which, I insulated with the same insulation. I additionally stuck small pieces of insulation over any visible gaps in adjoining panels, to stop hot air flowing back to the fuse box and brake servo areas.

3) I insulated the main distribution air duct that exits the evaporator, which is located directly under the center hood spline and behind the insulation block. To access the duct I removed the fuse box and the wiper motor shroud. I found that it was easier to push insulation around the duct as best as possible while it was in place. This modification seemed to provide an additional 1'-2' improvement over just doing 1) and 2) above

TESTING RESULTS FOR 1), 2) & 3) ABOVE Before these modification, the vent temperatures would start out in the low 40's in the winter and high 40's in the Florida summer. After approx. 10-15 miles of driving the vent temperatures would settle at approx. 52' with steady 35mph driving. I concluded that this was due to the engine cooling system heat soak. After these modifications, the AC seems unaffected by the heat soak, and now stayed in the 40's, approx. 9' below pre-mod temperatures. The heater system and solar energy, can be controlled. Heat soak from the matrix, to the A/C cold air flow can be reduced by shutting off the coolant flow to the matrix. The best way to accomplish this is Tony's Bypass Mod which works automatically with the A/C controls. An alternative is to install a manual shut off valve in the feed hose at the engine. As this is manual operation it may only be practicable for those cars in warmer climates were there is very little demand for the heater. If this method is used, I would caution that there is a re-circulation pump in the heater circuit, the purpose of which is to cool the engine after it has been turned off and the coolant temperature reaches 230’F. If the manual valve is closed, stopping the flow, this engine temperature safeguard will not work. The manual valve would have to be opened, if at engine shut down the coolant temperature is at 190’F or above. The reason for this, is because at this temperature the ECU is kept activated in order to turn on the recirculation pump if needed. I have performed tests with the heater feed hose clamped off, and then opened, the difference in my car, at the vent was 2’F, consequently, I have not done this modification.

EVAPORATOR COIL FREEZING

An additional upgrade is the installation of an electronic thermostat to replace the capillary based unit used on earlier models. This electronic thermostat was introduced on factory build at approx. February 2007. The unit has improved temperature sensing and faster reaction time, reducing the possibility of ice formation. It was possible under extreme ambient conditions of high humidity for ice to form on the evaporator core and restrict air flow past the temperature probe creating a “domino effect” which can lead to complete icing up of the evaporator core and little or no airflow to the cabin vents. Electronic Thermostat Retrofit Kit - Lotus No. A120P0149S Parts cost $142.87 END RESULT Cockpit is comfortable even on a 90' plus, high humidity, South Florida summer day. The vent temperatures maintain in the mid 40's in the 90' summer & an expected very low 40's in the 70' winter. No evaporator freezing, and, after vent temperatures creep up after being caught in slow/stopped traffic, recovery is quick, unlike previously. My system as a reference point, the dash vent temperature settles at approx. 45' below outside air temperature.