AirCon - not cold, but compressor working?

[andrewwynn]

Did you go through a phase where the AC would work for 5 or 10 minutes and then stopped working ? When the AC gets low on refrigerant it will usually get too good at getting cold and the evaporator will freeze into a solid block of ice. When there's a slow leak this is typical symptom that happens. There is a chart that says what the low side should be depending on ambient temperature I have a feeling that you just did not add quite enough freon. The high low numbers ratio looks healthy. We used to have to drive to Illinois to get R134a but now we can get it in Wisconsin.

Is the difference of how high versus how low that determines how cold the evaporator gets. When there is not quite enough refrigerant it's easier for the compressor to make a larger difference and it will freeze up the evaporator AC irony


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[andrewwynn]

@ upallnight: very cool find on the hack for the variable compressor


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[Crowz]

Originally Posted by upallnight

Automotive refrigeration system are designed so that the evaporator core does not get below 32 F. Why, when our refrigerator at home can get to a temp below 32F. Because unlike a refrigerator that has a frost free heating element design into it to eliminate ice build up on the evaporator, the evaporator in an automobile does not have this feature. And with the hot humid air that is drawn into the car, a lot of humidity is condensing on the evaporator. If the evaporator core was allowed to get below 32F, the water would freeze and block the incoming air from passing through the evaporator. This will prevent the air from cooling down so now you have warm air going around the evaporator instead of through it. When this happens you don't have cold air coming out of the vent.

A low side pressure also determine the coldness of the evaporator core. The lower the low side pressure the colder the evaporator can get. This is why the design low side pressure is usually around 34 - 40 PSI.

When I said valve I was referring to the valve in the compressor.

[wpoll]

Originally Posted by more_fasterer

Thanks for the advice guys. We can't buy R134a over the counter here in NZ for environmental reasons, so I'm gonna be stuck with taking the car to a service agent to get the aircon working properly.

While this WAS true, something seems to have recently changed and we can now get R134a over the counter.

SCA now have it - CRC AC Charge Refill & Hose - 400g - Supercheap Auto

And there's an auto-cool specialist up your way that sells online...CoolKiwi.

Welcome to Coolkiwi Automotive Enhancements | YOUR FAVOURITE DIY AUTOMOTIVE PRODUCTS

My cooling performance has dropped off a little over the last year - I think I have a very slow leak. Might try one of these one day.

*edit* I see CoolKiwi also does a gauge set...

R134a 2-Valve Air Conditioning Manifold Gauge Set | Welcome to Coolkiwi Automotive Enhancements

[andrewwynn]

On a recent help a friend job (that earned me my vaccum pump) I recharged a suburban that had a second evaporator for the back seat.

His pressure was 0psi all leaked out when I started so the first thing I did was draw down to a vacuum for 20 minutes or so to boil off any water and ready for recharge.

The first (of many) cans of R134a had leak finding dye and sealant. Sure enough there was one very obvious leak on a 90° connector that couldn't be removed without taking a lot of parts out (I suspect from a previous compressor replacement).

The dye stopped coming out within 30-60 minutes and the car was making cold AC months later when I followed up. I don't love putting leak fix when it's a part that can be re-done buy you may not even be able to tell where the leak is.

If you have weakening ac and are allowed to get R134a OTC then I recommend the basic refill kit with the gauge that also has the dial for ambient temp. It will do exactly what you need. If you get a can that also has florescent dye and seal that will be better if refilling is a repeat offender (I've seen AC still working after 20-30 years). If you recharge more than every 36 months but less than every 12, I would try a sealer before replacing parts.


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[more_fasterer]

Originally Posted by andrewwynn

Did you go through a phase where the AC would work for 5 or 10 minutes and then stopped working ? When the AC gets low on refrigerant it will usually get too good at getting cold and the evaporator will freeze into a solid block of ice. When there's a slow leak this is typical symptom that happens. There is a chart that says what the low side should be depending on ambient temperature I have a feeling that you just did not add quite enough freon. The high low numbers ratio looks healthy. We used to have to drive to Illinois to get R134a but now we can get it in Wisconsin.

Is the difference of how high versus how low that determines how cold the evaporator gets. When there is not quite enough refrigerant it's easier for the compressor to make a larger difference and it will freeze up the evaporator AC irony

Nope. The car isn't displaying any of the tell-tale symptoms of the evaporator icing up, i.e. there's no drop off in airflow into the cabin at any point, and (based on past experience) I would also expect to see the vents start to spit out fog just before it froze up - which doesn't happen either.

[more_fasterer]

Originally Posted by upallnight

What was the ambient air temperature when these readings were taken?

24deg C, which is mid 70's in fahrenheit.

[more_fasterer]

Originally Posted by wpoll

While this WAS true, something seems to have recently changed and we can now get R134a over the counter.

SCA now have it - CRC AC Charge Refill & Hose - 400g - Supercheap Auto

And there's an auto-cool specialist up your way that sells online...CoolKiwi.

Welcome to Coolkiwi Automotive Enhancements | YOUR FAVOURITE DIY AUTOMOTIVE PRODUCTS

My cooling performance has dropped off a little over the last year - I think I have a very slow leak. Might try one of these one day.

*edit* I see CoolKiwi also does a gauge set...

R134a 2-Valve Air Conditioning Manifold Gauge Set | Welcome to Coolkiwi Automotive Enhancements

Sweet, thanks!

[andrewwynn]

The strange thing is the lack of cold at idle but that could be a few at fault things. The variable compressor ok in full power not so good at low. Make sure of course the dash outside blend is set to the three blue dots


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[Crowz]

Mine does 42 to 44 degrees Fahrenheit at idle in normal and 36 to 38 at idle in recirculate mode with the variable compressor with it 90 or higher outside. Decent at least.