Technical A/C blows cold 4 min than hot and again cold etc

[vandeo]

I drive lancia musa but as far as I could see, climate control is the same.
So, here is the problem:
When I turn cooling, even on every setting (auto 24oC, 22oC or LO, etc), I receive cool air, and after several minutes, air is getting warmer. After several minutes of warm air, it starts again blowing cold, and it goes like than non stop, cold, warm, cold, warm. I cant receive constant cool air blowing.
What I did so far is:
Replaced AC preassure switch
replaced resistor for engine fan (for 2 speeds)
replaced condenser (old was in peeces).
Checked for preassures and coolant (freon) is there enough and recharged it.
Run diagnostics, in garage and while in garage, it woks fine, only makes problem while driving.
Thank in advance !

 

[vandeo]

This is exactly what I have donne so far

I noticed that ac is shutting off after several minutes of working fine.

It was all topped with gas.

First, I replaced preasuure switch (linear), no change.

Second, I noticed that second speed of ventilator is not turning on always when ac is on, and replaced the reostat .

Third, condenser was all in pieces, so I replaced it, along with drier.

Fourth, checked flaps in air vent and all flaps blow as it should and allow cold or hot air as it should, and while checking, again checked gas and preassure, on 42oC outside, low preassure was 3 nad high on 16 on idle and AC works fine.

On 3000 RPM high preassure was on 21 and low arround 6 and after several seconds on 3000 RPM, ac stops blowing cold, and few minutes past, starts blowing colds agin. Then after few more minutes again stops with cold air. Cold , not cold happends few more times and after that no more cold. When stops blowing cold, compresor and second speed of vent turns off.

Please help!

 

[Davren]

Do you have standard A/C or the automatic version with AUTO and MONO buttons?
.

 

[vandeo]

It is automatic but not like that. It is dual zone, something similar, with auto i mono buttons. I already have done actuator alignment, also tested flap position with bosch car diagnostic.

 

[aschiuta]

Too much refrigerant inside. At idle you must have maximum 2.5 bar = 36 psi better arround 2.3 bar = 33 psi on low pressure side.

 

[vandeo]

Too much refrigerant inside. At idle you must have maximum 2.5 bar = 36 psi better arround 2.3 bar = 33 psi on low pressure side.Ok? Bu

Ok. But it was put exactly 500 grams , as much as it should be?

 

[aschiuta]

Ok. But it was put exactly 500 grams , as much as it should be?

Depends by refrigerant type: R134a or 1234fy. 1234yf is much expensive and they are not interchangeable.
Also before put 500 g was extracted all refrigerant from AC circuit?

 

[vandeo]

Depends by refrigerant type: R134a or 1234fy. 1234yf is much expensive and they are not interchangeable.
Also before put 500 g was extracted all refrigerant from AC circuit?

It is R134a. Yes, extracted, Vacuumed and checked for leaks and then charged to 500g.

 

[aschiuta]

It is R134a. Yes, extracted, Vacuumed and checked for leaks and then charged to 500g.

For 134a the pressure is too high on low side. Extract 50-70 g from circuit and check.

 

[Davren]

If it's based on the Stilo version, try switching the ignition on (without starting the car), then hold both the AUTO and MONO buttons in and hold them in. That should reset the flaps. You should be able to hear the flaps moving. Don't release the AUTO and MONO buttons until the sound stops.
.

 

[vandeo]

Yeah, already tried alignment. With AUTO MONO and with Bosch diagnostic, no deal.

 

[aschiuta]

Yeah, already tried alignment. With AUTO MONO and with Bosch diagnostic, no deal.

This is low pressure of my Fiat Bravo 1.6 mjet overfill AC circuit = 45 psi = 3 bar. The photo was taken after 30 minutes engine running at idle and cooling fan worked on speed 2. I have manual AC so the cabin fan was at 3 speed and the air blow at 4 grade celsius temperature. Out side the temperature was 28-29 grade celsius.
Normal capacities of AC circuit is 500 grams but I overfill it with more 40 grams. My outside air recirculation flap is always open and this was the reason of overfilling. I have variable capacity compressor and the high side pressure was 19-20 bar and maintain even at 2500 rot/min of the engine. Also at 2500 rot/min the low side pressure is there at 3-3.2 bar.
So at your car is overfilling the AC circuit and is wrong to have 6 bar on low side pressure at 3000 rot/min.
Probably you have scroll type compressor which increase the compression ratio with the rotational speed.
This type of compressor works ON / OFF. When inside pressure in AC circuit raise too much the compressor is stoped.
The same effect of raising the pressure can be had if the regulating valve at the entrance to the evaporator is defective. You can read with diagnostic device the pressure in AC circuit from pressure switch located near the condenser radiator. The pressure depend on the outside temperature and it is same on low and high pressure sides as long as compressor it didn't work for at least 2- 3 hours.
4.8 bar at 20 grade, 5.7 bar at 25 grade, 6.9 bar at 30 grade, 9.3 bar at 40 grade for normal amount of refrigerant.
One week ago at 35 grade outside temperature on my overfill AC the pressure was 10.7 bar. Normal value is 7.9 bar.
So is less expensive to extract some amount of R134a to see what is happen.

 

[vandeo]

Ok. It is not bad to try with lower amount of refrigerant. But You are suggesting that expansion valve might be bad?

 

[aschiuta]

Ok. It is not bad to try with lower amount of refrigerant. But You are suggesting that expansion valve might be bad?

Yes can be because it controls the amount of R134 vapours which enters into evaporator. But it is expensive to replace so try first to lower the R134 amount.

 

[vandeo]

Ok. This is the epilog of solving my problem with AC.
Thanks everybody for help and advices, especially Aschiuta, because it was the expansion valve.
Who would know? You, obviously. .
Anyway, it is not that complicated to replace it. Or expensive. Just needed to lift engine cover (plastic with air filter in it) and behind and below is expansion valve placement. I went to my mechanic, we extracted refrigerant and 20 minutes later, after I removed old valve and put new one, replaced refrigerant back into car and after 1.5h of testing, driving and everything, it works perfectly!
Only one thing, about the price of the valve. For lancia musa, fiat idea, fiat bravo II, and several other models, valve costs around 50 euros, while for fiat stilo 01-07, valve costs 15 euros, and it is exact match, both physically and by specs.

 

[aschiuta]

Ok. This is the epilog of solving my problem with AC.
Thanks everybody for help and advices, especially Aschiuta, because it was the expansion valve.
Who would know? You, obviously. .
Anyway, it is not that complicated to replace it. Or expensive. Just needed to lift engine cover (plastic with air filter in it) and behind and below is expansion valve placement. I went to my mechanic, we extracted refrigerant and 20 minutes later, after I removed old valve and put new one, replaced refrigerant back into car and after 1.5h of testing, driving and everything, it works perfectly!
Only one thing, about the price of the valve. For lancia musa, fiat idea, fiat bravo II, and several other models, valve costs around 50 euros, while for fiat stilo 01-07, valve costs 15 euros, and it is exact match, both physically and by specs.

Nice works and good informations about valve.
Also will be nice to tell us the total cost of these operations.

 

[vandeo]

Well, actually, it is not as costly as it should be expected, because all work was done by me, recuperating refrigerant by my friend mechanic, and my doings were done in my friends garage (I am doing maintenance to all his computers , diagnostics etc so we are in some kind of simbiotic relationship , also, I frequently ask that I am the one to carry out all the manual labor because I think it is fair and I like to be the one maintaining my car)
So, only parts were paid,
- preassure switch arround 25 € (OEM, which I think is in china aliexpres arround 11 €)
- rheostat for radiator ventilator 15 € (also OEM, on aliexpres is 4 €)
- condenser was 60€, also OEM
- expansion valve was 15€ (as I mentioned, fits from fiat stillo 1.6 01-07)
In my place, discharging and recharging , with vacuuming and filtering gas and oil, costs 30€, for refrigerant
That is it.