What impact is A/C on MPG?

Does the A/C make much difference on the MPG for a 4.6 on petrol? Does the A/C have less of an impact due to the large engine compared to a Ford Focus or something or will it still use the same amount of extra fuel no matter what car it's on?

I hate the heat so what ever the answer, it's staying on until January.

I would say its minimal, have a look at your rev counter, when it kicks in, it will at most take an extra 100-200 rpm

I say that but it isn't strictly true mine is fubar at the moment, and has been for a year, i have tried 3 times so far to fix it to no avale, re gassing it changing parts etc, and its still a non runner......so its costing me nothing in diesel at the moment not to run it!! one day i will get it to work with all the other bits that don't work, and then it will over load and blow up on me

Dopey said:

I would say its minimal, have a look at your rev counter, when it kicks in, it will at most take an extra 100-200 rpm

I say that but it isn't strictly true mine is fubar at the moment, and has been for a year, i have tried 3 times so far to fix it to no avale, re gassing it changing parts etc, and its still a non runner......so its costing me nothing in diesel at the moment not to run it!! one day i will get it to work with all the other bits that don't work, and then it will over load and blow up on me

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Get it on a diagnostic machine, the HeVAC ECU generally diagnoses faults really well. Could just be a faulty sensor or something.

What have you replaced so far??

I lived without A/C for almost a year when I got my P38, now I have got it fixed and running I wondered how I ever lived without it ESPECIALLY with this heat and pollen in the air (damn hayfever). Get it on the diagnostic machine and see what it says then post back with the results.

A very very easy thing to check which was one of the faults on mine that had me chasing things for AGES is the cable to the compressor, its a green/yellow cable, has a blue connector just forward of the engine bay fusebox and then the wire goes down to the compressor plug. My wire had been damaged and pulled on so wasnt always making a good connection meaning I had very intermittent A/C operation. Once I got that replaced and the dodgy sensors replaced I was up and running. Splashed out on a new HeVAC panel that I could actually read and its been brilliant ever since <touches all the wood in the room>.

-Wills

97 DSE P38

The 1st half of my post went missing

I took it to Kwik Tit, had it gassed 3 days later it was empty, took it to an A/C guy, had it tested the top hose was leaking, had that replaced and tested, 4 days later it was empty again, i should have gone back i know but the blower had to be sorted out then as well
but tbh you get a little peeved with it all, now its getting hot again my mind is thinking sort it out now, so i might go up this week and have a word with him, oh and when i took it in to him to have a look, my blowers were intermittently turning off, i had to slam the drivers side dash at the bottom to get them started (i think the brushes had gone on them) took it out, can you just change the brushes?? no, you have to get a whole unit, lucky i got one off ebay for £10 tested it, it was fine and put it in and that's working anyway (im bitching a lot i know) you know where im coming from though, its just one dam thing after another

Rant over!!

Dopey said:

97 DSE P38

The 1st half of my post went missing

I took it to Kwik Tit, had it gassed 3 days later it was empty, took it to an A/C guy, had it tested the top hose was leaking, had that replaced and tested, 4 days later it was empty again, i should have gone back i know but the blower had to be sorted out then as well
but tbh you get a little peeved with it all, now its getting hot again my mind is thinking sort it out now, so i might go up this week and have a word with him, oh and when i took it in to him to have a look, my blowers were intermittently turning off, i had to slam the drivers side dash at the bottom to get them started (i think the brushes had gone on them) took it out, can you just change the brushes?? no, you have to get a whole unit, lucky i got one off ebay for £10 tested it, it was fine and put it in and that's working anyway (im bitching a lot i know) you know where im coming from though, its just one dam thing after another

Rant over!!

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I would get it refilled again with nitrogen and dye. Now keep your eyes open over the next few days for green (usually that colour anyway) spots anywhere along the A/C system. If you find any that represents a leak and the part will need to be replaced.

If you dont find any leaks then you will know its either electrical or a sensor in which case it would be good to have it hooked up to the computer to read the faults.

Have you checked your engine fusebox for corrosion, that can sometimes be a factor in dodgy blower motor operation, look for burnt relays etc.

Keep us updated with how it goes though!

Lastly, in answer to Mud Flaps question, I don't reckon I got anything more than 1-2MPG more when I didnt have my A/C working. I wouldn't disconnect it either in winter, the A/C runs all the time in a P38 hence the fact the interior doesn't steam up on cold days.

-Wills

I've experimented with AC on / AC off MPG loads of times and find it very difficult to get more than 0.5 mpg more with it off.

On a motorway run it's more economical to use the AC than have the windows open on something the size of a Range Rover anyway, aerodynamic drag makes sure of that.

wills said:

If you dont find any leaks then you will know its either electrical or a sensor in which case it would be good to have it hooked up to the computer to read the faults.

!



-Wills

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or it could be a blocked condensor or a faulty expansion valve or perhaps you have water or other contaminents in the system

slob said:

or it could be a blocked condensor or a faulty expansion valve or perhaps you have water or other contaminents in the system

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He went to Quick Fit though so I guess they would of evacuated the system and checked for those problems??

-Wills

The thing about Kwik Tit is its all just plug and play, no experience, if the machine didn't detect a vent, then as far as they are concerned there isn&#8217;t one, the A/C guy who specialises in A/C found a leak (he put a uv dye in the system) so i went up to Shepperton and saw the A/C guy 2day told him my woes and he has booked it in for 2morrow, and gona have a peep at it then, he was saying that the blowers have are important to the system, if there not working then it can lead to overpressureiation of the system, i suppose the A/C is coming out, and its not being dispersed??? i will have a look at the fuses now!!

wills said:

He went to Quick Fit though so I guess they would of evacuated the system and checked for those problems??

-Wills

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job experience **** quick fitter? ah wint bet on it

Just took all the A/C fuses out, under the seat and in the engine compartment took them out cleaned them up with ULC (an electrical cleaner) put them back....still no joy

but i have to say when you manually turn it off and on with the switch, the revs to rise and fall, so something is working there, i think im just gona have to wait till 2morrow and get it sorted with gas

slob said:

job experience **** quick fitter? ah wint bet on it

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Kwik Tit, plug it in to there brain box, and it empty's the system out, then puts a gas in it to pressurise the system, to test for any leaks, then if its all ok, it fills it up with the right amount of gas and pag oil

They put the make year and model of the car in to the "Brain" and it works it all out for them, so (hopefully) they don't have to think, the "Brain" replaces the Kwik Tit workers brain (a very,very,very,very, small micro chip)

And then it will all vent out 3 days later!!! and you go back to them and they say, the machine says.......no

if yer condensor is fitted in front of the rad as most are then you could have a ton of dead things inbetween them which will stop yer A/C from working. shouldn't take yer more that 20mins to check

Dopey said:

Kwik Tit, plug it in to there brain box, and it empty's the system out, then puts a gas in it to pressurise the system, to test for any leaks, then if its all ok, it fills it up with the right amount of gas and pag oil

They put the make year and model of the car in to the "Brain" and it works it all out for them, so (hopefully) they don't have to think, the "Brain" replaces the Kwik Tit workers brain (a very,very,very,very, small micro chip)

And then it will all vent out 3 days later!!! and you go back to them and they say, the machine says.......no

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most A/C machines use a vaccum to test for leaks and/ or the operator relies on leak detection dyes to show up.

best bet is first to ensure that the pump clutch is working and that yer condensor has a good airflow. If yer rad/condensor houseing has rubber flaps on it ,these flaps go hard after a while and stop letting the air pass through as they are no longer fexible enough to do so. and ave ah sed in another post check fer dead things blocking the air flow.
also if yer gas IS escaping over several day then you should hear a hissing from behind the dashboard (as the expansion valve starts to work overtime) shortly before you lose the required pressure to operate the pump clutch

if yer condensor is fitted in front of the rad as most are then you could have a ton of dead things inbetween them which will stop yer A/C from working. shouldn't take yer more that 20mins to check

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If it was that was the case (you mean crap dead fly’s, and the occasional dead sheep? a small one of course) its dead clean behind the rad (for the A/c) anyone have a link for taking the condenser apart and cleaning fitting back etc (if i can clean it?)

slob said:

job experience **** quick fitter? ah wint bet on it

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I took mine to Kwik Tit on Sunday for a re-gas.

The aircon was working when I took it in. It doesn't now.

Tiz the brain, its hurting me!! well we all now know not to go to Kwick Tit

all yer can really do to em is clean out the cooling fins with an airline and brush. dint use a pressure washer as it will fook it

Yea tiz all clean, behind it all, just a little oil and that,, but not on the cooling fins, of the A/C rad, when i get back i will give you a progress report, as to how much i have been fleeced

but have yer checked between the condensor and the rad