Renew Lotus Elise / Exige heaterbox and airconditioning system (hvac – a/c)

Back in 2015 i removed the entire climate conditioning system from my Elise, this included the airbox with heater matrix, cooler matrix (evaporator) and even the fan. It got replaced by a small race-style axial fan. The a/c pipes and hoses and compressor were discarded as well. The time has come to re-install the lot despite its weight, in favor of more comfort and authenticity of the car.

Unfortunately most refrigeration pipes were lost during the disassembly as most threaded connectors were seized up. In addition the sill pipes are under suspicion as the system never appeared to work properly with the previous owners. The condensor was dust, so in total every part needed replacement so i decided to put that project aside for a few years. But for this upcoming winter project on the Elise i started sourcing replacement parts.

A new heaterbox was sourced from an apparently new car converted into a race car, very happy with this item:

It replaces the old one which i may convert into a plug to take moulds at a later stage.

However, there is a difference between a 2zz/1zz setup and a 1ZR/2ZR box. The compressor is of a different type, and as such, the valve differs

2ZZ/1ZZ (111r) Bergstrom box B117P0029F replaced by A120P0018F includes expansion valve A117P0122S TBF 2…  id 32433

1ZR/2ZR Bergstrom box A120P0185F includes expansion valve A132P0107H TBF1.5D id 324317

I acquired the ‘wrong’ box so will have to re-use my old expansion valve.

These are the old cooler matrix (evaporator) on the left and the heater matrix on the right, positioned the way they are fitted in the box.

By design the heater is ALWAYS on, but a flap in the outlet (the Lotus sticker covers the servodrive) blocks the flow through the heater to some extent. Not ideal and will be replaced by a regulation of the water feed instead and a fixed flap position. The dash selector will be assigned a new task to achieve that.

Sill replacement hoses (as per service bulletin) and various OEM refrigerant pipes.

The Elise 111r (and all toyota driven Elises and Exiges) have the fan fitted on the drivers side and the airbox on the passengers side. The refrigerant pipe on my UK-RHD car is rather long as it has to circumphere the brake servo drum. LHD cars have the fan and box rotated, which brings the evaporator closer to the sill connection. As a result both low pressure refrigerant pipes have a substantial different length.

  • 111r and 2011>  RHD needs B117P0047F (the long one)
  • rover RHD needs A117P0048F (the short one, i have it surplus and is for sale)
  • 111r and 2011> LHD needs B120P0009F (not in the image)
  • rover LHD needs B117P0047F (again, the long one)

It could be considered to modify the entire system to the new greenhouse friendly R-1234YF refrigerant instead of R-134a gas. Unfortunately that is not immediately possible because the PAG46-8 oil in some re-used parts is not complient with 1234YF gas.

But since most parts are brand new – except for the compressor and evaporator – i plan to flush them and fill the system with ND12 anticipating a future conversion to 1234YF.  Lotus has started building cars with PAGND12 oil as standard and can fill it with both gasses. ND12 oil is also a PAG46 oil, but with additives, it will mix with PAG46-8 oil i expect.

A PAG46-8 filled system cannot be exposed to 1234YF. In addition the service ports are not complient and a refill with 1234YF is still 3 times the cost of 134a, but this will change in time. As off 2017 all new Lotus cars are 1234YF filled so in the future a breaker car could act as donor for new service port hoses  if necessary.

For now i will stick to 134a with ND12 oil and try to create a leak free system to save the environment a bit, 1234YF leakage would have 300 times less effect on greenhouse effect so it has a future.

All seals will be replaced by new HNBR o-rings (usually green, but lotus OEM parts come with black seals, which i will replace).

I have one seized up pipe to replace and a new sealed drier to source but that will happen.

The old original fan was collected from storage and tested ok. But it looks tired so the metal parts will be cleaned and replated again:

Cleaned in citric acid and about to be media blasted, ready for the platers;

Re-assembly phase


The ‘big’ SPAL fans have been removed from the radiator as the condensor will be sandwiched between the radiator and the ‘small’ SPAL fans which came of the car a few years ago. The condensor (elise-shop.com) is already provided with fittings to the radiator and fans.

The fan interface is become nice and shiny again,

As is the wiper mechanism;

Note (to self), the wiper mechanism can ONLY be removed and replaced with the air distribution plenum released from the bulkhead. However they must be retracted and replaced stacked together simultaneously because of limited space. If the the time comes, you will find out why.

The fan has been re-assembled with a replated face plate

The recirculation flap has been de-rusted and coated. All Tupperware boxes back in the bay after having wiped the bay down with cloth and ACF50 protection.

The fan and heater box can only be removed and installed with the clutch hydraulic pipe released on my RHD s2 111r. This may vary for the various types and RHD/LHD builds. The fan slides in and should be left tilted backwards to some extent to give way to the interface plate of the heater box.

The anti freeze sensor has been replaced with the later electronic thermostat kit from Lotus (through deroure part A120P0149S). This kit switches the aircon off in case of freezing up the evaporator. This used to be a capillar probe but has changed over to an electronic switch, fed by the 12volts of the air flap servo. It is actually a drop in replacement with all appropriate connectors. This should improve the reliability of the early s2 aircon system.

The heaterbox is installed by sliding it in outer edge first. This should pivot in the cavity of the chassis rails, and then be lowered to meet the fan interface. (Removal is the opposite).

The A/C valve sits on top of the heaterbox but this can be installed and replaced in situ. No need to remove the box.

Test fitment of various pipes and hoses:

Ford Fiesta by-pass valve sits on top of the heaterbox, adjacent to the dryer receiver.

Trinary switch:

Trinary switch R134a

H/P 28 kg/cm2 = 27.5 bar = 400 psi
M/P 17 kg/cm2 = 16.7 bar = 240 psi
L/P  2 kg/cm2 = 2 bar = 28 psi

This weekend i finished all A/C lines and purged it to 30 mm Hg vacuum using the coolant tank purge kit. Left it alone for a night and hooked up the vacuum gauge again. All vacuum was still there!

The system has been checked over (purged and nitron pressurized) professionally, and filled with 550g R134a refrigerant, ND12 oil was put in just prior to that.


The system is leakfree and now charged. There is some electrical problem which i need to sort as the compressor isn’t activated when engine, fan and aircon are switched on.

Everything you always wanted to know about the fan control box –  check here

Lotus Elise Exige Fan Control Module

I traced the fault to either a correded connector of the trinary switch (cleaned them) or a possibly required reset of the ECU by releasing the battery leads for a while. After that the compressor kicks in nicely! Happy times.

Observed pressures with 550g refrigerant at 19degC, car pushed outside to approx 13degC ambient

Engine off, cold system PS 64 psi - PP 64 psi - 4.4 bar
Idling, no condensor fan PS 27 psi - PP 112 psi - 7.7 bar
Revving, condensor fan forced by pulling coolant temp sensor PS 20-30 psi - PP 200 psi - 13.8
Revving, condensor fan automatic, off initially but kicks in at PP 270 psi 18.6 bar and reduces PP back to 150 psi 10.3 bar
Engine off, system PS 48 psi - 88 psi 6 bar (but that should level through compressor and valve)

The middle value of the trinary switch only switches on the rad/condensor fan after the pressure has increased to 270 psi and then stays on for a about five minutes duration, even if the A/C system is switched off and the engine is way below fan cooling. This is different to the manual which states that the fan(s) are always switched on immediately if the A/C button is pressed. I will have to look into that, combined with my observation that only one fan is driven at 12V instead of 2 fans at 6V each (parallel). I will try a different version of the ECU as well and solve the power to fuse problem at slot 14. [EDIT: note that this issue is resolved, read on for the solution]

How to debug a faulty Lotus Elise Exige A/C system?

  • Make sure it is actually faulty and you do not hear the clutch kicking in, if you do hear that it may be a stuck heater flap letting hot air in.
  • Is the cabin fan switched to either 1,2 or 3 (not 0)?
  • Is the light on the A/C switch blue?
  • Make sure fuse 19 is powered, that feeds the A/C clutch through the fan box relay and cabin fuse 4. (ref electronics)
  • I’d start with measuring the trinary switch. The low and high pressure switches should BOTH be normally closed in series and read 0 ohm (connects to pink – pink ribboned lead). If one them is open due to low gas pressure (or too high gas pressure) the series is open and the compressor will not be fired.
  • If the low pressure switch is open that may indicate the refrigerant is low on level or empty and have the system measured (professionally). If the A/C has been running many hours it may be the low pressure pipe in the sill corroded. Lotus provides replacement hoses for the sill pipes. Nitrogen pressurize the system to have them checked over.
  • If the low presure switch is closed (and presumably the high pressure switch as wel) inspect the thermostat terminals, the thermostat is normally closed (reads no resistance). This switch is in series with the pressure switches (pink wire) so all three should be closed at all times in ambient conditions.
  • I pulled the plugs from the fan controller and bridged 12V from pin 8 to pin 2 (both on the BIG connector).  This connects 12V directly to the pully (protected by cabin fuse 4 and should activate the pully clearly audible, (ignition on, but engine off). I you are uncertain about this, DO NOT DO IT and have it checked over professionally.  This test indicates a proper fuse c4 and pully clutch. (ref fan control wiring)
  • Failing that, you may want to check the signals sent out by the ECU – it grounds various pins to activate relays. For A/C activation it shoud ground pin 5. The 12v feed on pin 4 should also be present at all times, schematics here: fan control

Anyway, my A/C worked apart from the unusual fan activation. I mentioned that fuse 14 wasn’t powered by the upstream loom. To test the behavior of the system i diverted the 20A +12V fuse 3 (non existing) drivers window  to the terminal 14 input. Basically a 8 mm2 wire with a 15A fuse and spade AMP connectors on both side to plug temporarily into the fuse box. This would re-instate power on the fan switch box serial fan switch logic. So what happened?

  • engine on and cold, A/C off – nothing of course.
  • engine on and cold, engine coolant temperature sensor disconnected, emergency cooling kicks in at full blat (parallel, NOT according to the manual but it is a conservative assumption to run all fans on full if the coolant temperature is unknown to the ECU so that is not surprising.
  • engine on and cold, temperature sensor connected, A/C switched on, both fans immediately run in series at very moderate speed. Happy times! They stop as soon as A/C is switched off

Based on the behavior with only fuse 19 powered (and the manual) i assume the following will happen additionally:

  • half speed when coolant temperature is above 98 on rise (that will work now)
  • full speed when coolant temperature is above 103 on rise (it proved to do that, but only on 1 fan obviously)
  • full speed when trinary switch middle value senses 17-19 bar on the refrigerant A/C circuit  (this is NOT to be found in the manual)

I will confirm these events later. Next is to connect fuse 3 12V in to fuse 14 out in a safe and permanent way which may be reverted in time.

Basically, i have got a properly working A/C now!

I found that the wire to fuse 14 is very thin gauged and probably not up to the job. It enters fuse 14 at est. 1.5 mm^2 gauge and exits the fuse at est. 3.0-6.0 mm^2. Because the feeding wire was burnt some cm’s in front of the fusebox i had no power on the fuse. Fuse number 3 is fed by a sufficient gauge wire and also fused 20A. As i do not have electic windows this fuse is obsolete anyway, and a good source to feed the fan. I tested the fan with a 10A fuse with no problem on high revs, but left it with 15A for peace of mind. 20A isn’t necessary i think as the SPAL fans are rated 8 or 9 amps tops.I capped the abandoned feed wire to fuse 14.

From the manual:

The cooling fans are switched as a pair, and will operate at half speed (connected in series) when coolant temperature reaches 98°C on rise, and switch off at 94°C on fall. 
The fans will also operate at half speed irrespective of coolant temperature if the a.c. is switched on and the compressor is running. 
If coolant temperature rises to 103°C, the fans will switch to full speed (connected in parallel), reverting to half speed at 98°C.
The fans will also run at half speed, unless high coolant temperature dictates otherwise, when the a.c. is switched on and the compressor is running, or if the engine management system detects a fault with the inlet air temperature or coolant temperature circuits. NO, THOSE FAULTS WILL CALL FULL SPEED ON THE FANS

Random notes:

Seloc Junks may offer aftermarket new capped dryer/receivers – i ordered one but didn’t get to picking it up yet.

Read more about the electronic by-pass valve controller.