air-con not working

[mongoose]

My air-con has stopped working.A mobile a/c man has been to help and found that theres plenty of gas in the system,so its not the usual cause.The fuse is also fine.At the front of the car,behind the number plate,is a white connector block which comes from the loom and goes to the pressure sensor switch on the receiver drier.In this block is 2 live and 2 other lines,one of which is earth.The one live is from switched ignition,and this works,the other live,is live only when the a/c button on the dash is pressed,but in my case no live is present when button is pressed(blue light comes on as always).There is also no live feed to the compressor,even with the engine running.
The two relays in the footwell(changeover type)which plug into yellow connector blocks,are i think,related to the a/c system and test out to be ok.Are there any other relays related to the aircon?Or can anyone else help with pointers please?cheers,Mike.

[david beer]

Hi Mike
is this standard TVR or do remember something ?? I have fitted 3 AC kits to my "company cars" over the years. All to Mazdas where it fell out of the box onto the car. In all cases there were the low pressure sensor, the overheat exchanger sensor, the overheat compressor sensor and the anti-frost sensor in the "cold bit" tech talk there ! Oh, and there was also the "drop the AC when the foot is in the "shag-pile" well Jap-pile. What if you put 12v on the compressor pump, does it engage ? Being a "lecky" you could work backwards and make a bespoke reliable system ! Iam thinking of doing someting similar with the RR air suspension that keeps dropping to the bump stops, been in 7 times and a cost of £1500 and still does it. Oh these experts, expert rip off merchants, but dont start me. Wow, long ramble, been a long day.

[siwes]

your A/C system will have an LP low pressure cut out switch, usually lack of gas , are you sure your system is charged. did your A/C tech check the suction pressure should be around 3 bar running , very difficult to tell if there is gas in a non running system.
The system might also have an HP cut out in case of high pressure this is incase the fan is not doing its job on the condenser. if this has tripped then you will have to manually reset the cut out switch.
Finally there may well be a low lube oil switch on the system as the gas and oil go around the system together it is a differential pressure switch usually set a couple of bar above the gas suction pressure so oil pressure minus suction gives the true oil pressure.
Also check to see if you have power to the magnetic drive of the compressor, it might not be turning the compressor, in the worst case the compressor could be seized.
If the system has no gas it is pointless and expensive just getting it regassed , find the leak first
I take it that its synthetic gas you have in your system.More difficult to detect a leak than Freon R-22 or R-12 for that matter

[mongoose]

Cheers for the pointers both of you.The compressor will run if you give it 12v,yes there definately is enough gas in the system according to my a/c man.I've still to carry out a couple more checks over the weekend,but i think i'm getting there!I'm lucky enough to have the help of a fellow ph'er who also has a griff with a/c,and weve been doing some comparisons(circuit checks) by phone.Will let you know how i get on.
p.s.David,this car does have factory a/c,on my previous griff i had it retro fitted,but it was still done as per factory-well remembered!

[Mark Adams]

Mike - has it worked since you changed the management system?

Normally the A/C request is routed through the original 14CUX. When it sees a request, it opens the stepper a pre-programmed number of steps and then drops in the compressor a moment later.

The Omex 710 can apply an idle lift too if you are using an idle valve, when connected to the A/C Request line. However it doesn't control the compressor. If this is the case, you would need to interface the A/C Request and Grant lines together.

Only one thing you'd have to watch though, and it depends on the age of your loom. Usually the A/C Request line is active high (12Volts=request), and the Grant line is active low to switch on the compressor. Therefore you can't just join them together.

The two relays with yellow bases you have on your old 14CUX loom are for the A/C. One is the compressor clutch relay, and the other is the "A/C logic" relay that inverts the A/C Request signal.

[lig]

Hi Mark,

Sorry to hijack a thread, but I know that Mike won't mind as its me thats helping him out on the AC diags.

Can you tell me what my 5th relay is that is hanging off the loom? I have the two for the AC the two silver boxes for ignition and fuel pump and one other on a connector with a green base? I ask because Mike hasn't got this (no relay on the connector) and my car hasn't got any more than Mikes (to my knowledge), in fact it has less (no PAS).

Thanks in advance,
Lig.

[mongoose]

Mark Adams said:

Mike - has it worked since you changed the management system?

Thanks for the reply Mark,much appreciated.I honestly cant say when the air-con packed up scince the omex was fitted,but it has been only after,not before,so theres a good chance that its the culprit then.I traced one wire which should be live,sraight back to the heater control unit(no relay or anything else between)and when i opened up this unit i could see corrosion around the legs of two of the chips inside.Thus so far it has been my main suspect-i also dont hear a re-circ motor whirring when using that control knob either!
I dont use the stepper for isc at the mo,but i'd like to know how to identify and interface the grant and request lines,so that even without lifted isc,i can at least get the a/c runnin again!Can you lift the isc,just for the a/c,with spark scatter rather than use air bypass? The griff is a late 2000 model btw.Cheers,Mike.

>> Edited by mongoose on Monday 31st October 10:14

[jeffsy]

Air con??Air con???? What are you a man or a mouse!!!!

[mongoose]

Quinny said:

How involved would it be to just stick your old lucas ecu back in? If its pretty straight forward, could be worth trying.

Thats the next move.I already know that the lucas comes to no harm when left connected,as Shaun(v8d)wired it in this way deliberately,so that i could reverert to originality easily,at any time in the future.
Ive just received my heater control unit back from Lig,who kindly proved for me that the no.1 suspect was infact working ok with the a/c,but not with the re-circ.

jeffsy said:

Air con??Air con????What are you a man or a mouse!!!!

Us English deserve such luxury

>> Edited by mongoose on Tuesday 1st November 10:48

[Mark Adams]

Hi Mike

In order to help you with the wiring, I could do with a tad more info about the install. Am I right in thinking that you still have the 14CUX in situ? The wiring fix will be different according to whether it is present or not.

If so, then by cutting the 14CUX's outputs to the injectors only, you could leave it in control of the idle stepper and the A/C compressor clutch.

This is quite a common technique on modern cars where the original ECU cannot be extracted, due to being plumbed into so many other body systems. Effectively the Omex710 controls the fuelling and ignition, whilst the 14CUX looks after the idle and A/C. If you have coil packs on, you would have to feed the Omex tacho ouput to the 14CUX also.

You have to leave all the inputs, and just cut the output.

What do you think?

BTW have you got the GEMS coils in yet, or are you still on the dizzy (for distribution only)?

As far as I can make out, the 710 can apply an idle lift only when there is an idle valve. The older 700 used to do this with scatter spark - so I can find out if you'd like to know.

Lig - the fith relay (large black base with green top plate) is for the A/C condensor fan timer control unit. It is used on A/C Land Rovers, but never wired in on TVRs.

It's function is as follows. When the ignition is turned off, the 14CUX reads the fuel and coolant temperatures. If they both exceed programmed levels, then the 14CUX uses this relay to power up the condensor fans for ten minutes to reduce heat-soak.

The unit is actually a timer, used to drive the condensor fan relay coil.

When I have transplanted a 14CUX to a vehicle with electric fans, I usually wire in this unit because I think it's useful. In practice the fans very rarely come on, except after the car has been stewing in traffic on a really hot day.

[Mark Adams]

BTW - I like A/C as a Hayfever sufferer. The fuel cooler is very helpful too, and it is helpful to inject cool fuel (cooler the better).

[lig]

Mark Adams said:

Lig - the fith relay (large black base with green top plate) is for the A/C condensor fan timer control unit. It is used on A/C Land Rovers, but never wired in on TVRs.

Cheers for that Mark, why would mine have a relay in it then?? Guess I could just take this out. Could it be used as a spare? Are these relays used anywhere else?

Cheers,
Lig.

>> Edited by lig on Tuesday 1st November 17:01

[Mark Adams]

lig said:

Mark Adams said: Lig - the fith relay (large black base with green top plate) is for the A/C condensor fan timer control unit. It is used on A/C Land Rovers, but never wired in on TVRs. Cheers for that Mark, why would mine have a relay in it then?? Guess I could just take this out. Could it be used as a spare? Are these relays used anywhere else?

I've never before seen the A/C condensor fan timer control unit fitted in a TVR. It's probably not connected so you can leave it there, or leave the base empty! The unit itself actually has a couple of extra weird pins, so it won't go into a standard socket. Personally I'd just leave it there - it has no other use.

[lig]

Cheers for all your help Mark.


Kind regards,
Lig.

[mongoose]

Right,i'm getting really stumped now.With the 14cux plugged back in,the a/c still doesnt work.For whatever reason,the relays on the yellow blocks in the footwell are not switching,and there is still no 12v supply to the connector block at the front of the car,joining the receiver drier,as mentioned previously.The common denominator here seems to be white wires with a green tracer not having powerI now know that my heater control unit is definately working ok for aircon,as Lig has proved this for me on his car.
Mark,thanks for the reply.The omex system is running with the p38 coil packs.The lucas ecu can be removed completely as the fuel pump and tacho are now run from the omex,and until i realised the a/c wasn't working,i had had left the lucas on the garage shelf.

[Mark Adams]

Thanks Lig - nice of you to say!

Mike - there are a couple of white/green wires, so I'll be careful with my recommendations! The critical place is where it appears at the (yellow) base of the compressor relay. The functions of the wires (with relay terminal assignments) are as follows:

30 brown/green: battery feed (via 30A fuse)
87 black/green: to compressor clutch
86 white/green: ignition switched live (via 25A fuse)
85 black/grey: earthed by 14CUX to turn on compressor

If you have no 14CUX in the loom, then the A/C request and grant lines can be bridged from the A/C logic relay, which is the other yellow-based one. All you do is join the yellow/black (request) line form the logic relay to black/grey (grant) line on the compressor relay (described above).

Just one other note. If you run the Omex and the 14CUX in tandem, they will share some of the sensors. However they will both power the sensors too, which will mean they both get distorted readings (e.g. coolant temperature). This can be compensated for, but would mean you HAVE to run both ECUs.

O/T - aren't the P38A coil packs a neat fit?

[mongoose]

Hello again Mark.I think i'm getting closer,but still no joy!the omex is wired in seperately to the lucas loom as far as i know.Certainly,the coolant temp sensor is connected with a different plug,wired to the omex.So i now know that i cannot run the a/c using the lucas to grant the supply to the compressor etc.This aside,even when i bridge the grant and request lines,the a/c will never run as theres no switched live.Is this switched live supply direct from the ignition barrel?(does that sound right)or is something else in the cicuit between the barrel and the switched supply at the a/c relays?I take it that the 25a fuse to which you are referring is the one on the main fuseboard or are there any hidden ones?All my relays and fuses check out ok and the fuseboard contacts also seem fine.Its almost as if something is hidden,thats breaking the circuit,or that the ecu would normally control the switched live as well?.
BTW i agree that the p38 coil packs are a very neat install,very pleased with them thanks.
Anyway,of to try some more ideas with testing
edited to add:-just come back from more testing,.ignition barrel all ok,looks like the fuseboard will have to come out,i'm wondering if all the switched lives i'm looking for will come from the same connector block?

>> Edited by mongoose on Wednesday 2nd November 15:40

[mongoose]

Eureka!i've finaly found out whats going on!The white wire with pink tracer,which is found at the connector block at the receiver drier is made live from the heater control unit,then runs through the pressure switch,going back into the loom to supply the switched live to both the logic and compressor relays.I simulated this by applying 12v from a seperate source to this wire at the heater control unit end,and both relays had switched live feed 12v(white/green trace).The heater control unit should put out 12v to the white/pink wire each time the a/c knob is pressed,thus either the unit is faulty,or the a/c switch isnt doing what it should.The hc unit worked on Ligs car,so the switch is the main suspect now.Ahhh,much happier now

[Mark Adams]

Nice one Mike! I expect you'll be cracking a celebratory bottle later then....

[mongoose]

Mark Adams said:

Nice one Mike! I expect you'll be cracking a celebratory bottle later then....

.
Thanks for all your help,its all a little clearer now!Incorrect system pressure means no live switch feed to relays-obvious really isnt it

My next challenge will be finding out whats wrong on the control switch side! Cheers,Mike.