Air-Con Regassing ?

[fieldy107]

If re-gassing didn't work david there might be something else wrong, like a seized clutch. But if you had an air con guy do you re-gas he should of picked something like this up.

 

[VOLK]

Hopefully dyed it too so you can pick up the leak, I assume that's where it's going if the clutch kicks in and it doesn't cool.

 

[uzz320]

There can be many things that cause it to not cool properly besides being low on gas. It is best to get a set of gauges hooked up to check the pressures while it is running - this will give a very good indication of the problem. If there is a leak it will almost certainly be the shaft seal on the compressor unless some of the system has been apart or there has been damage to the condenser. You can also visually see if the clutch is engaging, so that one is easy to rule out (but a set of gauges will show that straight away). If anyone in SA has problems, I have the relevant tools and am happy to take a look and at least work out what is wrong.

 

[steveP]

Damn, I wish I knew that a couple of months ago. My air con system has been nothing but a headache. Originally it worked really well until the compressor died and let all the gas out.

I got a replacement from a member on here, got it fitted and regassed. The air con was never properly cold. You could feel it slightly on the max setting, but it wasn't right. Took it back to the place who regassed it and they doubled checked everything and confirmed there were no leaks and the gas was correct. I put up with it until the next summer.

I asked a few Mitsubishi guys as I believed it may have been an electrical fault. The compressor would switch on for 10 seconds, then switch off after another 10. They had a look and said the electrics were find and it's probably too much gas in the system and the pressure is wrong. Took it back to the air con guys and they released some gas. It still didn't work. If anything, it was worse.

I finally went to an air con specialist and he hooked up 2 pressure testers; one on the high side and one on the low. It turns out the low side pressure was incorrect. I think he overloaded it a bit with gas and now everything is much better. Probably back to how it should be; or at least 90% there.

 

[uzz320]

Funnily enough most air con specialists know stuff all about how to troubleshoot using their gauges (and then there are the mechanics that do regassing...). That is what prompted me to buy my own gear; i figured that if I was approximately 100x more intelligent (Which seemed to be the case) and it took them 5-10 years to master their trade (most never manage though it seems) it would only take me a bit over a month at worst haha.

If the pressures get either too low or too high it will turn of the compressor (there is a device in the system called a HPLP Switch; High Pressure, Low Pressure). The highside and lowside on the car are connected, it is a circulatory system - and the gauges come as a set attached to a manifold. If you turn off the car and wait long enough the two sides equalize and this will give you a rough idea of whether there is enough gas in the system - our cars seem to run about 100psi static pressure from memory. If the high side is where it should be but the low side is too high it can also be caused by the expansion valve being stuck open. Normally it is just that the high side is actually too high but they don't realize and just see that the low is too high (High side pressures vary more wildly with ambient temps and from car to car than low side pressures). If refrigerant is released and and the low side moves to where it should be, and the high side drops (and it starts working) then there was too much gas in the system.

It should be added for those who have no concept of how these things work, there is only a difference between high and low side pressures when the engine is running and the difference should increase as the revs increase (low drops, high rises, to a certain point).

 

[steveP]

Yeah, all that made a lot of sense. When I finally got my air con somewhat fixed, he showed me the low side dropping when the engine revved. He still thought the low side was too high when on idle though and it only reached optimum pressure when the engine was under load. The guy thought the compressor might be leaking/not holding pressure.

Does this sound right?

 

[uzz320]

Yeah, all that made a lot of sense. When I finally got my air con somewhat fixed, he showed me the low side dropping when the engine revved. He still thought the low side was too high when on idle though and it only reached optimum pressure when the engine was under load. The guy thought the compressor might be leaking/not holding pressure.

Does this sound right?

The low side pressures are more of a product of the gas level in the system and the expansion valve operation when the high side is at the correct pressure. If there is too little or much gas in the system both sides will be either too low or too high (generally). If the expansion valve is not doing its job, which is essentially controlling the rate at which gas passes from the high side to the low side - it is very similar to a thermostat - then you may see correct (or very close to) high side pressures and either too low (sometimes vacuum) or too high low side readings.

If the compressor was not working correctly, the high side pressures would be substantially too low (as it would not be compressing sufficiently). They normally rattle before they stop producing decent pressure, and often seize before as well. A leak that affects gauge readings would only last a few hours (or minutes) before all the gas was gone.

So, with all that said... I would guess that the compressor is fine, and also that the TXV is fine - it was probably just a hot day and the car had heat soaked the evaporator from sitting in the sun for a bit. This would mean that the TXV would open more than normal to try and cool the evaporator, raising low side pressures. All of the "expected pressures" are when the whole car is at a stabilized temperature so if the interior was especially hot from being in the sun, and the car brought in to the workshop, the condenser would shed the heat soak quickly as it sucks cool air from the front of the car at a rapid rate with the rad fans. The evaporator though has ducting that gets heated up and takes a while to shed the heat.

Was it taken for a drive to let it get to a stable state with the AC running then tested at idle when stopped?

If pressures are where they should be when the car is either moving or revving above idle, but not right at idle it is normally a temperature/airflow problem - if both sides too high, then condenser not getting sufficient cooling, if low side too high then the evaporator is getting air that is too hot (a common problem while testing in situation as above).

 

[steveP]

Yeah that sounds about right. It was a very hot day when it was tested. When I drove off the air con worked much better than at idle. All seems good now, so I'm happy. Thanks for all the info.

 

[marc mtp]

Had mine checked and regarded by a specialist but he says the heater is staying on as we'll killing the ac . The hot water pipes don't seem to switch off all the flaps and blend door are all working so Iam stuck please help i was told to stick a tap in the lines to stop coolant flow to heater but would rather fix it properly

 

[marc mtp]

All good was the blend door motor

 

[Lasiorhinus]

EDIT: Found it
Refrigerant: R-134a (HFC-134a)
Quantity: Approx 670-710g

I know this was a while ago, Trev, but can you remember where you found this info? The gas type is printed inside the bonnet lid, but where did you find the quantity? I need to get mine regassed and would love to have a reference to show the guy.

 

[BCX]

Japanese workshop manual has the info in the HVAC section. (chapter 55)

670-710g and has the operating/expected pressures too if you keep reading/translating. High pressure side should read between 1667kPa and 1765kPa at 1500rpm, blower speed high and on face mode.