Air-con for dummies

Armidillo

Armidillo

Well-known member
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Oct 30, 2010
Messages
4,145
Location
Armidale
Just to remove any doubts, I'm the dummy!

Am I correct that if gas pressure is low, then the evaporator temperature will be too low, leading to icing up of the evaporator?

Have just purchased a set of gauges - not planning to do my own regassing, more to satisfy my curiosity. I'm using the table from this page to interpret the readings I get: AC Pressure Chart | R-134a Temperature Pressure Chart

The aircon in my 605 works, but it is not very cold - in fact it is Ok when outside temp is below 30C, but pretty hopeless above 30C. Definitely not icing up! The gauges tell me that the gas pressure is low - 150/25psi (at outside temp of 32C). OTOH, my Xantia has pressures around 220/25psi, and works normally.

Can anyone suggest what might be wrong? Cooling fans both work normally, condenser cooling fins don't look blocked (engine runs at normal temp on very hot days, so cooling system seems fine). Also, the input (?) pipe to the compressor, which is cold in the Xantia, is luke-warm (output pipe gets very hot).

Cheers

Alec
 
Sounds like low charge because of the low high side


Garage C5 X7 3008 XTE
Gone but not forgotten 206 GTI 180 306 XR SED 405 MI16 x2 xzara VTS 406 SV 206 XT Berlingo 2011 (best car ever) 306 HDI 307 XSE HDI touring
Fix it right the first time
 
Bush Mechanic strikes again

LPG works as well as any refrigerant gas.

Note, Please do not smoke in vehicle if recharging with LPG

YOU WILL DIE DOING LPG in an aircond system, but it will work
 
Only when it leaks


Garage C5 X7 3008 XTE
Gone but not forgotten 206 GTI 180 306 XR SED 405 MI16 x2 xzara VTS 406 SV 206 XT Berlingo 2011 (best car ever) 306 HDI 307 XSE HDI touring
Fix it right the first time
 
Hi Armidillo,
You are definitely short of the correct refrigerant or your compressor is ailing. The poor cooling is due to there not being enough post compressor pressure, which varies with the ambient temperature, to cause the compressed gas to turn into liquid refrigerant in the condensor. So, with a gas liquid mix at the T X valve the cooling ability is lees than that of a liquid and your air con is challenged.
The mixing of gases is not a usual practice. LPG would work but its heat exchanging ability is likely to be very different, and more dangerous, than the correct, and probably inert refrigerant. Unless done carefully and with all the proper gauges and hoses et cetera the ingress of any air will require the use of a very efficient vacuum pump. A Hoover or Dyson would not cut the mustard.
Years ago car air cons used to have a sight glass fitted after the compressor. If watched carefully it was possible to very quickly know whether your gas situation was O K or needing a top up.
 
kelpiebat said:
Hi Armidillo,
You are definitely short of the correct refrigerant or your compressor is ailing. The poor cooling is due to there not being enough post compressor pressure, which varies with the ambient temperature, to cause the compressed gas to turn into liquid refrigerant in the condensor. So, with a gas liquid mix at the T X valve the cooling ability is lees than that of a liquid and your air con is challenged.
The mixing of gases is not a usual practice. LPG would work but its heat exchanging ability is likely to be very different, and more dangerous, than the correct, and probably inert refrigerant. Unless done carefully and with all the proper gauges and hoses et cetera the ingress of any air will require the use of a very efficient vacuum pump. A Hoover or Dyson would not cut the mustard.
Years ago car air cons used to have a sight glass fitted after the compressor. If watched carefully it was possible to very quickly know whether your gas situation was O K or needing a top up.
Click to expand...

Sight glass worked very well with R12 , easy to see if you had gas or liquid , but not so easy with R134.
 
Check out Hychill. Single charge bottles available from Bursons. It's a mix of LPG, butane and propane which gives it the same properties as R134. Never been an incident of "explosions" with it. In fact was the OEM gas for Oka vehicles for several years. The proportions by weight to the R# gases is about 1/3. And being heavier than air, if there is a leak very little leaves the system unless the leak is at the lowest point in the system. Less pressure and bigger molecules so less likely to leak too.

I've used it in my old Pajero to fix a slow leak of R134. Been there 2+ years and still working well even in Sydney's current heatwave.
 
R134a is also heavier than air, and has the advantage that the system was designed for it.
 
Does anyone have an opinion on whether low freon/R134a pressure can cause icing of the evaporator, or does it just cause aircon to be not very cold?

Cheers

Alec
 
Can't comment on refrigerants, sorry.


I owned a very good 605 for about 11 years. (Great car should never have replaced it.)


The A/C fooled around for the last 2-3 years.


I found it was caused by a poor battery post connection. Should have been my first check not last.


Another dummy.
 
Armidillo said:
Does anyone have an opinion on whether low freon/R134a pressure can cause icing of the evaporator, or does it just cause aircon to be not very cold?

Cheers

Alec
Click to expand...

No opinion just facts no it cannot cause that .[emoji106]


Garage C5 X7 3008 XTE
Gone but not forgotten 206 GTI 180 306 XR SED 405 MI16 x2 xzara VTS 406 SV 206 XT Berlingo 2011 (best car ever) 306 HDI 307 XSE HDI touring
Fix it right the first time
 
Air con not very cold would be the norm. But, if the blower was u/s or an impediment to the ingress of air to be blown through the evaporator then it could be possible that ice could form. Not at all likely, but possible in certain circumstances.
 
Your better off looking at the low pressure gauge
with air con turned off the pressure in pounds
should match the outside temp in farenheight
that indicates volume of gas in system Now with air running
on high idle the l p should be 38. The h p values vary a lot
Depending on temp outside. The l p doesn't.
If it's low static and running your gas is low.
If it varies then your pump is questionable
if you put some by hychill in don't go over 38
cause overgassing is not gonna help Regards Fish
 
Fish said:
Your better off looking at the low pressure gauge
with air con turned off the pressure in pounds
should match the outside temp in farenheight
that indicates volume of gas in system Now with air running
on high idle the l p should be 38. The h p values vary a lot
Depending on temp outside. The l p doesn't.
If it's low static and running your gas is low.
If it varies then your pump is questionable
if you put some by hychill in don't go over 38
cause overgassing is not gonna help Regards Fish
Click to expand...

Thanks Fish - that looks like really useful guidelines! Just going on the low pressure, I've definitely got low gas volume!

Cheers

Alec
 
Thanks everyone for contributions - been meaning to find time to post a sensible response, but this will have to do instead...

I'm concerned that I may have another problem apart from low pressures - eg TX valve.

Re. evaporator icing up when gas volume is low - there is evidence for this, but it seems more common with household air con:
https://www.achrnews.com/articles/135634-causes-of-and-cures-for-an-iced-evaporator
AC evaporator freezes and no cold air coming through vents - Maintenance and Repair Forum - j-body.org - The J-Body Organization

My personal experience with icing up - the underdash aircon in our 504 used to do it (never solved it). More recently it was happening in a Landcruiser. Fixed by a service, which I understood included topping up gas, but maybe they cleaned the evaporator (no pollen filter in 105 series). It does seem that restricted air flow is a big factor

Anyway, I was asking because my 605 has low pressures and doesn't ice up. As I thought that the icing up was caused by low gas, I was wondering about what other components might prevent proper cooling.

A bit of history: bought the car - a Series II 605 - in 2009, with 72,000km. Aircon not working... At that time I didn't have my own pressure gauges.

A vac down (no obvious problems) and a regas in an Armidale workshop got the AC working, but after a year or so it stopped, and this time I was told it needed a compressor.

Got a new compressor fitted, and requested that Hychill be used. Didn't actually see label on cylinder, but that's what I was charged for. Alas, it wasn't very cold, but the guy who did the job was in Tamworth, and I don't go down there (about 120km south) very often, so put up with it.

After a year or so the gas leaked out. This time I got a guy in a body shop in Tenterfield to refill it with R134a. He again confirmed that it held vacuum well, and suggested the source of the leak must be the Schrader valves (filling points) - a good thought, as the vacuum leak test can't test the valves.

Here's the weird bit - the guy in Tenterfield ran out of gas before he had delivered what he believed to be the correct charge, but the aircon worked anyway, and was COLD for once. At the time I concluded that Double Chevron and others were wrong about Hychill - it might be OK for old vehicles that originally used R12, but didn't seem to be a suitable replacement for R134a. I also began to think that a lower charge than specified might run colder...

Anyway, after a couple of years the gas leaked out again. The same workshop in Tenterfield agreed to do the regas (not the same guy though), but it was only after I had booked a time that I discovered that Schrader valves aren't all the same, and that no-one in Tenterfield or Stanthorpe had anything remotely like the ones from the 605 :rolleyes:, and I had left too little time to order the right ones, so probably the cycle is going around again. To get the right amount of gas, the guy looked up a table of weights and used what he believed to be the right amount. However I believe he said that his high side gauge was not working, so pressures were not checked.

That brings us to where I am now - AC freshly regassed, compressor not very old, compressor is definitely working, but the low presure pipe just before the compressor never gets more than a little cool, and nor does the cabin air. High pressure pipe gets too hot to touch, so I'm guessing compressor works.

From a visual inspection, the condenser doesn't look at all dirty or blocked, and the cooling fans are working well. I'm wondering whether the gas weight for the 605 in published tables for the aircon industry might be too low :confused:.

If I'd known that air con gauges were so cheap and freely available, I would have bought a set years ago, instead of just trusting people to get it right, and then assuming that if there was still a problem after a regas, then my car's AC must have other problems.

Cheers

Alec
 
The receiver drier could be blocked it's just a block
Of synthetic filter that absorbs moisture blocks up
Breaks up and causes flow problems.
Just had a 405 that did all except get cold changed r d and
put in till reached 38pounds l p it took a while but settled
down and is cold and efficient. I did what ur doing got gauges
And some high chill and started learning. It's kinda fun getting sorted
 
Hope it's not the receiver/dryer, as that was replaced along with the compressor.
 
OK, how come none of you Hychill advocates mentioned this :
https://www.hvacrnews.com.au/news/hychill-issues-statement-on-factory-fire/

So the stuff is definitely inflammable :eek::eek:.

The only retail outlet I've been able to find up here that stocks it is Bursons, and my nearest Bursons is Tamworth or Port Macquarie. Bit of a downer to walk into Bursons Port Mac, only to be told that they've got no stock, and don't know when they will again!

Cheers

Alec
 
Do you know for certain that the Hychill gas was connected to the fire?

quote from article..."we know that the fire damaged the office and warehouse building, but that the main storage and cylinder filling facilities remain intact."
 
You must log in or register to reply here.
Top