Weird F355 AC issue

Sounds like the condenser is short of cooling air, i assume it has a fan so is it working. When you are driving the air is cooling the condenser by the forward movement of the car, but when you stop the fan should be doing this, obviously it is not doing this and the gas is not being cooled, hence the hot air blowing into the interior

 

I am not a 355 expert so it a bit of guess work on my part- looking at the drawings it seems you have 2 off water radiators , each with an electric fan. The left hand radiator should have another radiator bolted to it, this is actually the air conditioning condenser and this is the one which seems short of air flow to cool the gas. Each of these radiators has an electric fan probably mounted on the rear side. You need to see if the fan on the double radiator is running when the air conditioning is on. If not then start checking fuses etc. Point to be carefull of here is this fan on the left hand side seems to cool the engine cooling water and the ac condenser. The fan on the right hand side just does engine cooling water from what i can make out. If that is the case you may be driving around with only half of your engine cooling system working.
Start the car and put the ac on, see if both fans cut in when the water gets hot and regulate the engine water temp, also see if you get cold ac air. If only the right hand fan cuts in then you have to see if you have voltage to the left hand fan motor and go from there.

 

Have a look at the diagram on the eurospares web site, 355 heating and cooling page 022. Cooling system radiators, shows 4 rads but only 3 are highlighted.

 

Before anything, start the car and bring the revs to 2000 rpm and see if the a/c is cold while the car sits there.

 

LH fan operates by a water temperature sensor in the top of the radiator. It maintains 190 degrees water temperature but, if I recall correctly, also runs continuously when the AC compressor is running. This cools both the water radiator and the AC condenser which is mounted in front of the LH radiator.

The RH fan operates by an oil temperature sensor mounted on the RH side of the oil filter. This sensor feeds the ECU which in turn controls the RH fan cooling both the RH water radiator and the oil cooler mounted in front of the radiator.

For water temperature, the LH fan always comes on first with the RH fan only coming on if the LH can't maintain 190 degrees by itself. Otherwise, the RH fan only runs if the oil temperature exceeds a certain limit (forget the number, two hundred and something....see the manual).

 

Going by what hjp is saying above, as he knows more than me. To test the left hand fan you could try allowing the water to come up to temperature and see if the fan cut in, if it does not then find the wires to the temperature switch in the top of the left hand radiator and try to disconnect a wire or connect the 2 wires together. If the fan starts then your problem is elsewhere. Also have a look at the front of the car to see if you have got a plastic bag stuck in the air intake.
See if the fan rotates freely and no slack in the bearings etc.

 

Agree with Pap. Start by revving the car to 2500RPM while in the same conditions you are reporting the problem under (idling while hot). If the A/C stays cold while revving but gets warm when you let it idle normally at 1000RPM, then you have a potential refrigerant undercharge situation. If the behavior is the same at all RPMs while at a standstill, then you have a condenser air flow issue, which is what others are suggesting you look at above.

 

I need to make a small correction in my post.

The RH fan comes on by a thermistor (heat variable resistor....as heat goes up, resistance goes down) located next to the oil filter. It is monitoring water temperature coming out of the heads, not oil temperature. This feeds the ECU which controls the RH fan. At 203 F, it turns the fan on, thus, its a back up for the LH fan (LH fan comes on at 190 F and goes off at 180 F). The oil temperature is controlled by an ECU operated valve that lets oil flow through the cooler.

 

+1