Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[drmryan]

Hi guys,

We've got a '98 ZJ Grand Cherokee and with the exceptionally hot weather, I thought it was time to recharge the AC which was blowing warm.

I got one of those R134 recharge kits from Hellfrauds, but with it charged it only seems to blow cool, not cold air. It's pressured to about 45psi (I think). Much above that the recharge pressure gauge goes into red so I don't want to overcharge.

The Haynes manual doesn't say what pressure it should be at, but I'm wondering whether the 'this range is green' on the generic gauge is insufficient for this particular car. I've tried it with the accumulator plugged in and with the connector jumpered to keep the pump engaged. Or should I be looking for a problem elsewhere? It's holding pressure ok so it's not leaking.

TIA

Daz

[Lukemagnum]

That 45 psi tells me that the liquid in the evaporator (the bit that does the cooling) is boiling at about 10 deg C. I have worked on industrial chiller plants for 30 years and to determine if a system is working correctly and if it’s correctly charged I would need more temperature measurements and the high side pressure.

The best way of charging most air con systems is by weighing in the charge, for a car this is info can be found on a nameplate under the bonnet.

Over charging may not increase this pressure by much but it can cause very high pressures in the condenser (the radiator at the front of the car) and can cause pipes to burst leading to serious injury so be careful, I wouldn't recommend linking out switches to hold in the compressor either as these could be safety cut outs and have the same results.

Back to your original question, I wouldn't expect an R134 system to run any higher than 45 psi, but in my experience a lot of A/C faults in the summer are due to blocked condensers, I would start by checking this and giving it a good clean with a hose from inside the engine bay to the front and make sure that the fan is running correctly. I do this every year and mine runs ice cold without the need to visit Halfrauds.

[willo]

O

[willo]

O

[willo]

Not being funny but u say the system is holding charge, therefore there are no leaks, why did you need to recharge it?

What was the system pressure before you added some refrigerant?

[The Transporter]

Wohah!!! The guy said 45psi, he made no mention of the engine running so I'd be inclined to say that we are talking 45psi of standing pressure... These Halfords kits only contain a small quantity of R134a, the rest of the can is either some kind of PAG lube or an agent that causes the O rings to decompose and swell, thus sealing small leaks round the O rings but it is just a short term fix... that doesn't realy work anyway....

It is an accepted fact that car aircons leak a small quantity, the quality of systems is abysmal, they leak even more if you don't use the aircon.... They are not sealed like cold stores or domestic comfort coolers and so over several years you can lose the refrigerant...

Having said that, an elderly Jeep will have a good chance of suffering advanced corrosion in the condenser, pipework, springlock fittings and evaporator so it is wise to take yourself to a specialist who will pressure test the system with Nitrogen before shoving any refrigerant in there... Alternatively most tyre bays have the equipment to recharge systems.. They have units that measure vacuum loss over a period of a few minutes... Although this may find large leaks, small leaks go undetected but I suppose that the equipment and operatives comply with the box ticking exercise that is Kyoto......

By the way Drmryan... Always apply a good vacuum to the system before charging and ditch the Halfords crap

[bgbazz]

Wohah!!! The guy said 45psi, he made no mention of the engine running so I'd be inclined to say that we are talking 45psi of standing pressure... These Halfords kits only contain a small quantity of R134a, the rest of the can is either some kind of PAG lube or an agent that causes the O rings to decompose and swell, thus sealing small leaks round the O rings but it is just a short term fix... that doesn't realy work anyway....

It is an accepted fact that car aircons leak a small quantity, the quality of systems is abysmal, they leak even more if you don't use the aircon.... They are not sealed like cold stores or domestic comfort coolers and so over several years you can lose the refrigerant...

Having said that, an elderly Jeep will have a good chance of suffering advanced corrosion in the condenser, pipework, springlock fittings and evaporator so it is wise to take yourself to a specialist who will pressure test the system with Nitrogen before shoving any refrigerant in there... Alternatively most tyre bays have the equipment to recharge systems.. They have units that measure vacuum loss over a period of a few minutes... Although this may find large leaks, small leaks go undetected but I suppose that the equipment and operatives comply with the box ticking exercise that is Kyoto......

By the way Drmryan... Always apply a good vacuum to the system before charging and ditch the Halfords crap

 
Listen to the wise words..he is right on the money with this. Anyone with a vehicle fitted with A/C should be giving it a 5-10 minute burst every week or so all through the year, regardless of the temp, because hoses and pipes can dry out and crack..seals dry out and shrink. Having owned more than 40 vehicles with A/C over the years, I have seen more than a few of the problems which can pop up from time to time, but can honestly say that that I've never gone the DIY route to have them solved.

I'm not taking the piss out of anyone trying to help you..we all will give our best.

[willo]

O

[willo]

Wohah!!! The guy said 45psi, he made no mention of the engine running so I'd be inclined to say that we are talking 45psi of standing pressure... These Halfords kits only contain a small quantity of R134a, the rest of the can is either some kind of PAG lube or an agent that causes the O rings to decompose and swell, thus sealing small leaks round the O rings but it is just a short term fix... that doesn't realy work anyway....

It is an accepted fact that car aircons leak a small quantity, the quality of systems is abysmal, they leak even more if you don't use the aircon.... They are not sealed like cold stores or domestic comfort coolers and so over several years you can lose the refrigerant...

Having said that, an elderly Jeep will have a good chance of suffering advanced corrosion in the condenser, pipework, springlock fittings and evaporator so it is wise to take yourself to a specialist who will pressure test the system with Nitrogen before shoving any refrigerant in there... Alternatively most tyre bays have the equipment to recharge systems.. They have units that measure vacuum loss over a period of a few minutes... Although this may find large leaks, small leaks go undetected but I suppose that the equipment and operatives comply with the box ticking exercise that is Kyoto......

By the way Drmryan... Always apply a good vacuum to the system before charging and ditch the Halfords crap

He made no mention of either so you also may be incorrect

[The Transporter]

Perhaps willo, I frequently am... but 45psi head pressure is too low, 45psiback pressure means that he would probably have cooling and 45psi standing pressure means nothing..

[Mike Pavelin]

The pressure of R134a varies hugely with ambient temperature. With the system charged and turned off, and at a temperature of 75 degrees F, you should see a pressure of 78psi. With the AC running and at 75 degrees F ambient temperature you should see pressures of around 40-45psi on the low (suction) side and 150-175 psi on the high (discharge side)

[willo]

Perhaps willo, I frequently am... but 45psi head pressure is too low, 45psiback pressure means that he would probably have cooling and 45psi standing pressure means nothing..

I concur, its been a long day, i'd quite like to remove fridge From my head, at least for the next 8 hrs, and now mike wants to talk in funny numbers, meh, take it to a specialist

[UKJeeper]

Mike is about as close to a specialist as it gets...

[willo]

Mike is about as close to a specialist as it gets...

Tim its easy enough to read a comparator, perhaps we should start discussing k factors and heat enthalpy charts...

[drmryan]

Jumpering the connector to the accumulator was recommended in the Haynes manual as a method of getting the compressor engaged in order to charge it if it's tripping out due to low pressure - it was.

The 45psi is at the low pressure port with the engine running and the AC on. I don't have the equipment to check the high pressure side.

And the system was low when I bought the car last year, I just never got round to recharging it until now. I guess the PO never used it.

I'll check the condensor for blockages and see how that goes.

Thanks for the replies so far.

Daz

[UKJeeper]

Mike is about as close to a specialist as it gets...

Tim its easy enough to read a comparator, perhaps we should start discussing k factors and heat enthalpy charts...

Not sure what you're trying to prove there Will. 

[Hillbilly]

Ok my brains hurting now. My air con blows coldish but certainly not freeze your nuts off low. Can I hold a thermometer to one of the vents to see if it's blowing as cold as it could or is that just plain stupid. 

[Mike Pavelin]

Mike is about as close to a specialist as it gets...

Tim its easy enough to read a comparator, perhaps we should start discussing k factors and heat enthalpy charts...

Not sure what you're trying to prove there Will. 

Dunno. Obviously as I was trained by the manufacturer on the exact product in question I know nothing, but am attempting to answer a layman's questions in simple terms. In my experience, fridge mechanics do have a tendency to speak in language that most people don't understand (presumably in an attempt to justify their existence/salaries) which isn't very helpful here. I, too speak refrigeration gobbledygook, but it is pretty useless when answering questions on a car enthusiast forum.

I'll now f**k off and leave it to the experts.

[gazjeep]

The pressure of R134a varies hugely with ambient temperature. With the system charged and turned off, and at a temperature of 75 degrees F, you should see a pressure of 78psi. With the AC running and at 75 degrees F ambient temperature you should see pressures of around 40-45psi on the low (suction) side and 150-175 psi on the high (discharge side)

To Dymryan ...... go with what Mike says dude 

[UKJeeper]

Ok my brains hurting now. My air con blows coldish but certainly not freeze your nuts off low. Can I hold a thermometer to one of the vents to see if it's blowing as cold as it could or is that just plain stupid. 

Not stupid at all mate. That's often a test that's done, from what i've read.

[UKJeeper]

Edit: walking away.

[willo]

Mike is about as close to a specialist as it gets...

Tim its easy enough to read a comparator, perhaps we should start discussing k factors and heat enthalpy charts...

Not sure what you're trying to prove there Will. 

Dunno. Obviously as I was trained by the manufacturer on the exact product in question I know nothing, but am attempting to answer a layman's questions in simple terms. In my experience, fridge mechanics do have a tendency to speak in language that most people don't understand (presumably in an attempt to justify their existence/salaries)
I'll now f**k off and leave it to the experts.

It seems you must of worked with my colleague, i never understand what he waffles on about and he definitly needs to justify his existance

[willo]

Dymran if you do find your condenser is blocked or dirty, then if you can find any, use some nitrogen to blow out the dirt from the fins, failing that some compressed air will do.

You may just find that your system doesn't have the duty (it may be labouring due to age amongst other things) in this lovely warm period we find ourselves in no doubt Mike can confirm what max ambient these systems were designed for.  I note today has been a bit cooler. Its all relative and your system will work much better in cooler ambient temps, sadly the time you want it to work is when its redders outside, which for us fridge engineers is when we get busy and earn megga dosh cos of incompetent mechanics lol that go before us, isn't that right Mike? But then again i type this whilst at work on my 5th consecutive 18hr day...

[The Transporter]

PAH! You fridgies get no sympathy from me, you've had the last five years off due to the non Summers that we have had so it's about time you lot did a bit.....

I've frequently found that those fluffy seeds that blow about tend to get through the condenser and accumulate between the condenser and radiator and they are a devil to get out... I prefer to use a garden hose with a finger over the end to clean the condenser as compressed air can either bend over the fins or if they are corroded, blow them out all together...

The Jeep CCOT system has in my opinion always been a bit lacking and does struggle in some US and Middle Eastern temperatures but is more than enough for a UK Summer.... Even one with sunshine and mine cycles off at 3c

One tip for that the OP could use to work out if the airflow through the condenser is the issue would be to use a themometer in the centre vent with the air flow passing through the air vents at full speed engine at 1500rpm (Doors open, bonnet shut) and note the temperature when the temp is stable, then get an assistant to spray water at the condenser and note if the vent temperature drops noticably... if it does then air flow could well be you issue. Check the fans are working correctly too!

[willo]

 Trickling water over a condenser, my favourite get out of jail free card.

I am busy at the moment cos my colleague is on holiday rather than the heat, my stores are all working fine.... :-)