A/C Loss of Refrigerant Theory

[wwest]

Like most everyone else each spring I have to "top off" the refrigerant, now R134, in my '88 Carrera. A/C specialists have checked over for leaks many times in the past 16 years of ownership, and most recently when it was converted to R134 about 2 years ago.

First, my theory, and then an explanation.

When the car is parked with the engine and EXHAUST still HOT, convection airflow will HEAT the rear lid mounted condenser, likely very seriously so. How high might the resulting refrigerant pressure reach on a really hot, BRIGHT, day thrown in..?

My pressure was at 65PSI this evening simply setting in a nice cool, ~55F, garage.

Suppose, at the instant the ignition is switched off, part of the condenser, and all of the line to the recvr/dryer, and the dryer itself are FULL of liquid refrigerant, just as should be the case. The evaporator blower has also just been switched off reducing the heat exchanging capability of the evaporator significantly...AND...no compressor VACUUM. The high side pressure, LIQUID pressure, will now leak down VERY slowly.

Might the high side pressure in that circumstance, BOILING whatever liquid might remain in the rear lid condenser, get high enough to begin leaking around the o-ring couplings...?? System leaks slightly, pressure subsides, until the next time.

Anyone ever taken system pressure measurements in a situation as above.

I'm thinking of revising my engine lid condenser fan system so it runs at half power with the engine switched off but with the high pressure compressor disable pressure switch open.

Note: There is a REASON why my '01 C4 has an engine compartment cooling fan.

[c337cc]

Like most everyone else each spring I have to "top off" the refrigerant, now R134, in my '88 Carrera. A/C specialists have checked over for leaks many times in the past 16 years of ownership, and most recently when it was converted to R134 about 2 years ago.

First, my theory, and then an explanation.

When the car is parked with the engine and EXHAUST still HOT, convection airflow will HEAT the rear lid mounted condenser, likely very seriously so. How high might the resulting refrigerant pressure reach on a really hot, BRIGHT, day thrown in..?

My pressure was at 65PSI this evening simply setting in a nice cool, ~55F, garage.

Suppose, at the instant the ignition is switched off, part of the condenser, and all of the line to the recvr/dryer, and the dryer itself are FULL of liquid refrigerant, just as should be the case. The evaporator blower has also just been switched off reducing the heat exchanging capability of the evaporator significantly...AND...no compressor VACUUM. The high side pressure, LIQUID pressure, will now leak down VERY slowly.

Might the high side pressure in that circumstance, BOILING whatever liquid might remain in the rear lid condenser, get high enough to begin leaking around the o-ring couplings...?? System leaks slightly, pressure subsides, until the next time.

Anyone ever taken system pressure measurements in a situation as above.

I'm thinking of revising my engine lid condenser fan system so it runs at half power with the engine switched off but with the high pressure compressor disable pressure switch open.

Note: There is a REASON why my '01 C4 has an engine compartment cooling fan.

Does the car still have the original non barrier hoses??? If so ,it will leak using r134 in the system. I replace all rubber hoses & seal rings,new drier & exp valve & cure the problems. The cooling fans in the 996 cars are there for a different reason,not for the condensor. Cond is mounted up front on 996,rear in a 88. If you want to make that 88 A/C cold,talk to Charlie @ Griffiths techinal.

Howard