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Old 1 Week Ago
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Default Aircon Freezing up I think?

I seem to be having an issue with my updates aircon. Blows cold most of the time, super cold sometimes (see mist coming out) then suddenly it will shut off the cold air and old blow non-cold air out.

If I turn it off for a bit, it will sometimes come back on pretty quickly.

The aircon clutch is engaged, I am thinking that it is freezing up? Anyone had a similar experience?
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Old 1 Week Ago
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Quote:
Originally Posted by Jimmyb View Post
I seem to be having an issue with my updates aircon. Blows cold most of the time, super cold sometimes (see mist coming out) then suddenly it will shut off the cold air and old blow non-cold air out.

If I turn it off for a bit, it will sometimes come back on pretty quickly.

The aircon clutch is engaged, I am thinking that it is freezing up? Anyone had a similar experience?
I have seen this on various makes over the years, and you are likely correct the evaporator has likely got a layer of frost on it which makes it go warm. By design the system manufacturer tries to prevent the evap running colder than 2C to prevent ice build up but sometimes due to drift in calibration they will operate lower than freezing and if the location is humid then bingo, they freeze up.

They go warm because quite counterintuitively ice and frost are very good insulators.

Clear the evap drain outlet you may have condensate sitting in there, and by selecting a higher cabin temp setting sometimes will help.
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Last edited by Classic Boy; 1 Week Ago at 08:57 AM.
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Yes mine does the same . The evaporator is freezing up
Especially on low speed it seem to happen quicker. The drain tube is clear but still freezes . The AC low pressure switch is supposed to cycle the AC clutch on and off . Changed 2 of them already but still no on-off switching of ac clutch so I've give up and just turn it off-on manually .
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Originally Posted by amlav View Post
Yes mine does the same . The evaporator is freezing up
Especially on low speed it seem to happen quicker. The drain tube is clear but still freezes . The AC low pressure switch is supposed to cycle the AC clutch on and off . Changed 2 of them already but still no on-off switching of ac clutch so I've give up and just turn it off-on manually .
I read somewhere you hot wire and bypass the switch is a fix
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Jimmy, a bush fix I used in a kenworth was to block half the radiator opening off, worked to an extent but not a cure. High humidity & poor design gives problems. The proper fix was adjustable thermostat & reposition the evaporator so it didn't hold the water in the core. BTW Kenworth = JUNK. Also aircon man said my bush fix would make the system explode, but it didn't happen, lots of other things on it did though, even the driver occasionally. Blocking half the radiator on an xj may also bring on an explosion.
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Default A/c

The evaporator if it is icing up doesn't go warm but blocks airflow over the evaporator so that little to no cooling of the air takes place.

Bypassing the low pressure switch will ensure that you freeze up the evaporator and the compressor will run non stop.

Blocking half the radiator so you decrease the A/C systems efficiency increases the High side pressures and put the system under more stress!! It would also allow the low pressure side to rise above the cycling pressure and probably keep the clutch engaged. not sure if I'd call that a fix.

Why don't you replace the low pressure switch and just fix it properly.
I'd prefer to see what the system pressures are doing first though before I started swapping parts.

Seriously some of the suggestions that get thrown up on here

Heres the manual description of the low pressure cycling clutch switch.

The low pressure cycling clutch switch is connected
in series electrically with the high pressure cut-off
switch, between ground and the Powertrain Control
Module (PCM). The switch contacts open and close
causing the PCM to turn the compressor clutch on
and off. This regulates the refrigerant system pressure
and controls evaporator temperature. Controlling
the evaporator temperature prevents condensate
water on the evaporator fins from freezing and
obstructing air conditioning system air flow.
The low pressure cycling clutch switch contacts are
open when the suction pressure is approximately 141
kPa (20.5 psi) or lower. The switch contacts will close
when the suction pressure rises to approximately 234
to 262 kPa (34 to 38 psi) or above. Lower ambient
temperatures, below approximately -1 C (30 F), will
also cause the switch contacts to open. This is due to
the pressure/temperature relationship of the refrigerant
in the system.
The low pressure cycling clutch switch is a factorycalibrated
unit. It cannot be adjusted or repaired
and, if faulty or damaged, it must be replaced.
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Yep . The low pressure switch should cycle the AC clutch on-off.
Changed 2 low pressure switches on mine but for some reason still
no on-off cycle. If I remove one wire from the low pressure switch it will turn the ac clutch off as it should . I've released a bit of the gas from the system too , thinking maybe is to much gas in it .
Still did not help. Not keen on releasing more gas .
What I've done than I've connected a fridge thermostat in series with the low pressure switch and wrapped the thermostat tubing around the ac piping . That fixed the on-off cycling but sometimes the thermostat contacts don't close properly (maybe dust getting in them) ,just a gentle tap on it brings it back to life .(got to change it...one day) .
Having the ac cycling on-off help reduce the engine coolant temperature too..especially in the hot days .
To change the low pressure switch is no big deal , there is not much gas that can escape but when screwed back in it should be just hand tight .

Last edited by amlav; 1 Week Ago at 02:04 PM.
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Hey Jaffa, I only used it as a temporary thing to get me home for the aircon man to throw some more parts at it. When it gets up to 50c in the shade you do whatever you can to get some cooling. Also had a switch to shut off power to a/c compressor which was probably better than blocking radiator. The evap was mounted horizontally with fans pulling air upwards through it so it held the water in the core & froze quickly. Eventually got an aircon guru on to it, he rejigged the whole thing. He mounted the evap vertically with much higher cfm fans blowing through the evap core & adjustable thermostat, then it actually had airconditioning. Brown & Hurley/Kenworth Brisbane response was we won't cover that under warranty, tried to back out of anything else which may have been a warranty job also. They had a huge condenser out front which was the grill called a grilldensor. Blocking half of it never caused engine cooling problems, the hotter the outside temp was the better it went, it liked to run between 105c & 110c coolant temp. Jimmy, sorry for the anti kw rant, even after 25+ years it still gripes me.
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