I had me AC regassed by kwikfit 4 weeks ago, working great until I really needed it in the recent heatwave when it's died completely. How can I check if its lost its gas ,at home, or its another issue like something electrical? I have a home compressor. My initial thoughts were to power the ac compressor (2001 dhse) direct ,briefly, with the engine running to see if it then cools but chickened out in case I damaged something. I 'think' I can check for pressure by momentarily depressing one of the valves on the bulkhead? If no pressure or very little could I then pressurise the system with my compressor then spray joints with soapy water to test? But what pressure is safe? Very new to 38's and never had ac before so green with that too, do have a nanocom though!
Thanks a bunch for any advice!

If KwikFit did it, take it back and tell them it has stopped. They should pressure test it for you. Presumably the compressor clutch isn't engaging? That can be a result of the air gap being too big and usually means it will engage when the temperature is warm but it doesn't when the weather is hot when you need it most. Set the AC on Lo which will cause the HEVAC to attempt to engage the clutch and, assuming you can get to it easily on a diesel, tap the clutch with a screwdriver handle. If it engages then, the clutch needs a shim removing from behind it to get the gap back to where it should be (between 16 and 30 thou).

You can very briefly press in one of the valves but be careful or you'll get a face full of refrigerant and PAG oil if it does have pressure in it (this is also illegal as you are releasing fluorinated gases into the atmosphere and contributing to global warming). If you've ever used one of the self fill cans, they often have a gauge in the hose and will have the correct fitting to go on the port. R134a systems are pressure tested to 10 bar (around 145psi) and you should really be using Oxygen Free Nitrogen and then a vacuum pump to get it all out again. Compressed air preferably dry, can be used as long as you vac it out immediately you've finished the test. If you have lost the refrigerant, the most likely leak point on a P38 is the top left (looking at it from the front) corner of the condenser where it has a piece of foam on it. It has almost certainly had leak detecting fluid put in it at some point in the past so you will see a green stain which will glow under UV light.

Cheers Richard, silly question time, sorry!
Where is the clutch? In front or behind the pulley? Can't find anything googling just "tap the clutch" . I plan to have a look Saturday, access is not good but should be better with the under tray removed. Might be obvious where the clutch is when I get a good look but just incase.....

The ac compressor and clutch on the diesel is buried on the RHS right at the bottom of the engine making access difficult.
You can get to it if you take off the front RH wheel arch liner. The clutch clearance is set by swapping different thickness spacer washers.

Oh, I know where it is alright, the compressor that is. Just not sure where to tap it to help engagement of the clutch.
Taking the liner out is a pita if mudflaps are still fitted I discovered hahaha 😆

The clutch is on the front of the AC compressor. You've got the bit the belt goes round that spins freely and behind it is the actual drive to the compressor. The clutch is electromagnetic and pulls in against a spring so when it engages both parts spin and not just the bit on the front. All you do is tap it to give it a hand to pull in.

Sorry if a bit off topic...

Years ago an ex's uncle was a rep for an engineering firm. His firm 'designed' a system that allowed hydraulic systems on vehicles such as cranes (Palfinger type) to be powered by the vehicle engine instead of by a separate engine or an electric motor. He started describing how this system worked... a hydraulic pump driven by the engine but which could be disconnected from the engine (so the pump wasn't running all the time) just by pressing a button on the dash. "What, like an AC compressor clutch?" I asked. '"Yes just like one of those"... And he got a £50k bonus on top of his salary for selling such systems to fleet managers, seemed like his job was too easy...

Back on topic.

If you went to KwikFit for a re-gas its quite likely that it hasn't been properly filled. The P38 system takes a lot of refrigerant and, as with Halfords, the standard price refill may well only buy you just enough gas to get the system working not a full fill.

Best to go to proper specialist.

Way back in my beginner P38 days I had a couple of Halfords re-fills that only lasted 6 months or so. Pimple faced Halfords youth said no faults on the car "they re all like that and need to be done every few months". Third time I collared a very knowledgable young lady from National AirCon who was doing my neighbours car on his drive. Hardly managed to get past Halfords before she said it had only been about half filled. Which proved to be the case.

She reckoned KwikFit and the other chains that do air conditioning as a side business were about as bad.

Mind you all that gas is expensive, my bill was about twice next doors! Must be 5 or 6 years since its last fill and it was plenty cold enough over the last couple of weeks.

Clive

A mate has a workshop doing routine servicing, MoT failures and stuff like that. No end of times he gets customers coming in to have work put right that has been done by Halfords. They should really stick to pushbikes...

I did the full FGas course so I can install domestic and commercial air con systems (and for some unknown reason have been very popular in the last few days) but took the automotive exam at the same time so am qualified to do that too. To do it properly you use a recovery machine to remove any remaining refrigerant, then pressurise with Nitrogen, leave for 30 minutes to ensure the pressure doesn't drop due to any leaks, at the end of that time use a vacuum pump to remove the Nitrogen and any remaining air that may have been in the system, before refilling with the correct quantity of refrigerant.

The likes of KwikFit and Halfords use an automated machine (that way their staff don't need to be sent on a training course and pass a City and Guilds exam). It recovers any remaining refrigerant, skips the pressure test phase and goes straight to the vac stage. As long as the system holds a vacuum, it assumes no leaks then puts refrigerant in but has to be programmed before the start with how much. Some need it entering as a figure in grams, with others you tell it what car and it uses a look-up table to set the amount. However, if you ignore that setting it uses a default quantity of (usually) 600 grams. Considering a GEMS needs 1250, a Thor 1380 and a diesel 1100, you get a half filled system which will work but not very well or for very long. Easy way to check is to put it on Lo and shove a thermometer in the vent. If it goes down to 5 degrees C or lower, it's working as it should (out of interest, I checked mine the other day and was getting 3.9 degeres with an ambient of 29 degrees). If it can't achieve that, you've been given a short fill.

2 Of my cars are Jap imports and not usually listed on automated machines, a sticker under the bonnet says they should take 950grams of refrigerant.

Some firms charge one price for a recharge with up to 1kg of refrigerant, a higher price for more than 1kg. Got to wonder how wide spread this practice is and whether the vehicle manufacturer calculated that the ideal amount of refrigerant should really be 1050grams but went with 950grams to save dealers/customers money in future or to meet some sort of 'green' criteria?

How accurate are the machines at measuring weight of gas they recover and refill with?

I do use a Kwik Fit for AC charging but at this Kwik Fit they let me watch and give a little input, so I can make sure they set the machine to charge with 950grams (or a bit more). A lot of these places normally make customers wait in a lounge but if you turn up in overalls and work boots, explain that you're a mechanic (you're not going to break your ankle tripping over MOT brake rollers etc), understand the AC system and personally replaced components on it, have some concerns about it or how it's to be filled etc, some will let you watch the technician do the work. Or go somewhere else..

I can see the nitrogen test makes sense if the system is suspected of having a leak, because it is possible for a vacuum to close a leak only for the leak to return when the system is under pressure (although a vacuum test will still find the vast majority of leaks?). But surely if your aircon is still working OK a few years after it's last maintenance/regas (so the only reason for a regas is maintenance) there won't be a leak and the nitrogen test isn't necessary? While the system still needs to be vacuumed to get all the old stuff out?

If you've had a leak on an AC system and some of the oil has been lost, how do you know how much oil should be put in (besides obviously the amount of oil that was recovered by the machine) when recharging? Don't machines just put the same amount of oil back in that they recovered (and although they can recover all the gas they can't recover all the oil)?

Popped in to my local LR indy this morning and it's booked in for next Thursday for a look see and a tracking check too.
Hopefully they will be more "knowledgeable ".
Meanwhile I'll remove the slam panel and see if there is damage to the condenser or anything else obvious.
I'll also put a stick it note on the steering wheel with the gas weight which will either annoy them or make them grateful for my assistance in the matter. Hahaha (because I don't like using LOL).
I'll try the clutch tapping too.

Had a bit of unexpected free time so I've been fiddling. As I was on my own ,with no pair of helping hands, I rigged up some cable and a switch and powered the compressor directly, there is a connector on the rhs inner wing, with the engine running and working the switch I could see the clutch working fine and both parts being driven, engine note changes too (diesel). Then, when I knew what to look for, I reconnected the original wire to the compressor, HEVAC on low , AC switch ON and restarted the engine and got back underneath, the compressor clutch is working and the pump is turning.
No cold air though.
Grill and slam panel off and I can see no deterioration to the condenser paying close attention to where the foam bits sit, all looks tickerty boo.
Being as the clutch/pump is turning does that mean any switches and/or sensors in the circuit are OK and it's likely just low gas from being short changed at kwikfit and maybe a slight leak adding to the mix?
I'm guessing the clutch wouldn't pull in if any of the sensors/switches were bad?
Then again, I wouldn't expect the clutch to pull in if the gas was low but it does!
I could see some black dirty oil mist around the pipes going into the condenser but I suspect that was from an old oil leak at the power steering pump which I fixed a few months back.

It's obviously got enough gas in to close the pressure switch which is in series with the compressor clutch, but not enough to give you noticeably colder air. If you poke the AC Off button so it doesn't try to engage the clutch, set it at Lo and stick a thermometer in one of the vents with the engine running, you'll measure the temperature of the ambient air being drawn through the system. Then poke the button again so the compressor engages and watch the thermometer, chances are you'll see a small drop in temperature which will confirm a low charge.

A pressure test is more reliable than a vacuum test, the vacuum is to draw out everything in the system before filling it. I've just got in from installing a domestic system so have been testing at 43 bar as they run at a much higher pressure than an automotive system. If there's a leak, that will soon find it......

Thanks Richard.
I'll try the thermometer test tomorrow.

I want to get a UV torch to check for AC leaks after the dye is put in, seem cheap enough on ebay, anything I should be watching out for before I buy? Would I need special goggles to see the 'glow' too? It's just in the long distance past I think I saw a guy wearing some and using a uv lamp to find a leak on some compressed air plant where I was doing some plumbing work, must be 15 yrs ago or more.

The cheapy UV torch I got with a water leak detection kit works fine in dark or subdued lighting. Insufficient contrast out in the daylight.

Draping a blanket over the open bonnet to form a makeshift dark tent works OK (ish) daytimes.

The UV filter goggles made to enhance contrast by, mostly, only passing the fluorescence wavelengths may help but I'd always understood that they were primarily made to allow the safe use of higher power UV sources. The ones I had at RARDE were dark enough to make midday twilight. But the UV source I was using was dangerously powerful. I suspect the cheapy UV torch I have now simply wouldn't generate enough fluorescence to be usefully clearer.

The fluorescent stuff hangs around for a fair while so if someone else has used it before things can get confusing.

Clive

Question re leak testing….
Im planning on using nitrogen to pressure test but am unsure as to the mechanics of the AC system.
If I add the Nitrogen to the low pressure side how much of the system gets tested? Will the Nitrogen pressurize up to the Expansion Valve and back to the Drier or will it go as far as the Evaporator and then back to the drier, or to where? Same question re the High Pressure system.
I suppose the question would be whether or not the system is split and if so where is the divide between High and Low pressure?

The simple answer to that is - just like when a Vacuum (test) is deployed - ALL parts of the system are effectively 'reached' so to speak, and similarly if you use Pressure instead. Unlike refrigerant in a working system these is no Gas/Liquid phases involved for 'inert' gases of course.

(The 'high pressure' side originates from the compressor (as gas) which reduces through the Condenser/fan as it cools (to liquid) but if there is a "divide" per se that could be considered the Expansion Valve... and it is then the Liquid/Gas transition in the Evaporator that produces the cooling - if that helps..).

As a 'rule of thumb' it is always best to do anything on/via the Low Pressure side of course

Incidentally - again considering the possible size of your leak - I really do hope you are not planning to use dye when you pressurise with Nitrogen !

Whilst I am not disagreeing with your point re “all parts being vacuumed or pressurized”, I’d have to ask why does my High Pressure vacuum hold a vacuum and the Low side will not? That’s what had me ask the question. It’s not making sense to me why one side will hold and the other will not> There has to be a “shutoff” somewhere in the system that’s separating the readings.
Im not using dye for the leak test. Pressurized Nitrogen and soapy water is all.
My concern is that the “bloody leak”, as I am now calling it, one of the connections at the Evaporator. Correct me if Im wrong, but if my memory serves me correctly, there are no other fittings between the firewall and the Evaporator. With the Expansion valve being within the engine bay the High and Low pressure pipes then run directly to the Evaporator….
All the parts to the AC system are brand new but I never pressure tested it before installing the dashboard and all the trim within the cabin, which is my own fault…..
The only hope is that the “bloody leak” is within the engine bay……

davew wrote:

(The 'high pressure' side originates from the compressor (as gas) which reduces through the Condenser/fan as it cools (to liquid) but if there is a "divide" per se that could be considered the Expansion Valve... and it is then the Liquid/Gas transition in the Evaporator that produces the cooling - if that helps..).

Wrong way round. The compressor sucks in gas and it turns to liquid under pressure and gets hot in the condenser, which is why the condenser has cooling fans. The liquid then goes through the expansion valve where it boils, turns into a vapour and draws heat (to use the correct term) and gets cold. Same as using a lot out of a Calor gas cylinder when the liquid turns to a vapour and the cylinder gets cold, sometimes cold enough for condensation, if not ice, to form on the outside. The vapour passes through the evaporator (not strictly correct terminology as it evaporates at the expansion valve) drawing more heat from the surrounding air giving the the cold. That vapour then goes through the compressor and the cycle starts again. The low pressure side is where the refrigerant is a vapour and the high pressure side is where it is a liquid.

As to why one side will hold a vacuum and the other side won't, I've no idea as it is a closed circuit. If doing a pressure or vacuum test, it shouldn't matter which port you use because of that. The only time you can have problems is if there has been a leak in the past which someone has tried to fix with a leak sealer and it has sealed something that shouldn't be sealed. But if everything is new, that is pretty unlikely. The domestic systems I am installing only have one port which on the low side but as they are reversible to heat as well as cool (the compressor can reverse so the condenser becomes the evaporator and vice versa), when heating that port becomes the high side.