AC - one side colder than the other??

[harlie]

Hi Guys.

Bloody AC - had an interesting one on the weekend.

When the car is first started (hot day) with the AC set to 21 both sides it does:
*fan speed full (tick)
*air flow upper vents (tick)
* freezing air coming out passenger side - cool air coming out drivers' side (cross)

It takes about 15min to get the cabin down to the set level at which stage the fan speed has reduced to what I would say is normal and interestingly both sides even out in temperature - they are both now very cool - not freezing but the drivers' side is now colder then when the fan was full speed - the volume of air passing through the evaporator has reduced by 50%+.

The system maintains the cabin temperature without issue however it takes far longer to get it down initially.

I was thinking blend motors/flaps right up until they evened out. Also, when I turn the temps to 28 (max) both sides swap to blowing very hot air within the same time. So the coolant valves are ok and the blend flaps are operating?

I'm pretty sure that the refrigerant gas is low as I've had the symptom of the condenser icing over (several times) lately and the TX valve has started a faint whistle - both common symptoms with low gas.

My question - can uneven cooling between sides be contributed to low gas? Is it a case of the liquid to gas evaporation is finished before it crosses the entire matrix and with high air flow the energy is gone from one side? Is it a stage just before it can only produce cool air?

[chaybra]

Hi Guys.

Bloody AC - had an interesting one on the weekend.

When the car is first started (hot day) with the AC set to 21 both sides it does:
*fan speed full (tick)
*air flow upper vents (tick)
* freezing air coming out passenger side - cool air coming out drivers? side (cross)

It takes about 15min to get the cabin down to the set level at which stage the fan speed has reduced to what I would say is normal and interestingly both sides even out in temperature ? they are both now very cool ? not freezing but the drivers? side is now colder then when the fan was full speed - the volume of air passing through the evaporator has reduced by 50%+.

The system maintains the cabin temperature without issue however it takes far longer to get it down initially.

I was thinking blend motors/flaps right up until they evened out. Also, when I turn the temps to 28 (max) both sides swap to blowing very hot air within the same time. So the coolant valves are ok and the blend flaps are operating?

I'm pretty sure that the refrigerant gas is low as I've had the symptom of the condenser icing over (several times) lately and the TX valve has started a faint whistle ? both common symptoms with low gas.

My question ? can uneven cooling between sides be contributed to low gas? Is it a case of the liquid to gas evaporation is finished before it crosses the entire matrix and with high air flow the energy is gone from one side? Is it a stage just before it can only produce cool air?


I would presume there is only 1 evaporator element and the amount of air taken from that is what determines the temp coming from the vents (Old school system) and as the evaporators in cabin are usually thicker than wider I couldnt imagine that the cooling differences are vastly different... only a presumption.

try the battery disconnect trick as the control module could be playing silly buggers for the thermostat?

[harlie]

ok, for the record, in case someone else comes across this, I will answer my own Q.

Low refrigerant is responsible.

Makes sense when we look at the evaporator - it is a plate & fin laminated type with the tubes running vertically so the refrigerant slowly moves from one side of the evap to the other. Vents for each side are drawing air from that side of the evap - When the refrig is low, by the time the liquid (it's more likely a gas before it has entered now) moves across the evap it can't absorb anymore heat.
I assumed it was like the condenser that has the tubes running horizontally, so the refrigerant moves from the top to the bottom - wrong.

[rar110]

ok, for the record, in case someone else comes across this, I will answer my own Q. Low refrigerant is responsible. Makes sense when we look at the evaporator - it is a plate & fin laminated type with the tubes running vertically so the refrigerant slowly moves from one side of the evap to the other. Vents for each side are drawing air from that side of the evap - When the refrig is low, by the time the liquid (it's more likely a gas before it has entered now) moves across the evap it can't absorb anymore heat. I assumed it was like the condenser that has the tubes running horizontally, so the refrigerant moves from the top to the bottom - wrong.

So no leak behind the dash?

[harlie]

Don't know yet. It has been recharged with Dye.

The evap leak theory was given to me by a big AC shop in towards town, they claimed to have checked all over the front and the only parts left are behind the dash. However, I now know whats involved in removing the front fan (to access the condenser) and there is no way that they did that - so they haven't checked over the condenser at the front for starters.

Speaking of the front fan, it hasn't worked since I have owned the car. The big shop didn't mention it but everyone I've spoken to since rang loud alarm bells. Now that it works I can see condenser pressures are down from just over 400psi :o to about 250-280. Several people have mentioned that at that pressure it surely must have been leaking on the high side - which is not inside the car. Keep in mind that those pressures are only high when there's no air flow like in city traffic, but it's enough.

Also what I have noticed is a suspicious build up on one of the high pressure flex hoses that looks a lot like the pictures of the leak seal goop solidifying.

Add to this that I've still not found anyone mentioning changing the evap on a L322 - I know I could be the first, but do you know how ****ed I would be after all that work for it to still leak :mad:

So in short, I'm looking for a light (UV) and glasses (apparently they are yellow) and in a month or so I will pull the front end apart and have a propper check for dye - there's a couple hours in that which I want to do before I commit to the couple of days getting to the evap.