R34 GTT AC short cycling ? Normal behaviour?

[George.]

Hey guys,

Just want some advice on r34 GTT ac system. Since I’ve owned it, the ac compressor, doesn’t matter the set temperature or ambient temperature, runs for around 10 seconds then disengages the clutch, then re-engages everywhere 30 seconds or so and keeps repeating this. 
 

is this normal?

 

I had it recharged today as it was slightly low and thought it would fix it but still does it.

it cools fine in summer even prior to the recharge, except for the usual warmup when stopped or in traffic (still yet to wire overheat fan to on with ac)

 

any thoughts would be much appreciated 

[GTSBoy]

Is the pressure switch healthy?

Have you put the control unit into diagnostic mode to see what it has to say about faults?

FWIW, it should not short cycle like that. In fact, the fact that is is "climate control" means that the compressor should usually stay on all the time, and the controller blends the super cold air from the evap with heated air from the heater core to achieve the setpoint you're asking for. The only time when it doesn't do that is when it is set to "ECON" mode. I think.

[Dose Pipe Sutututu]

If it's cold in summer, then no issue.

If it's cutting out every few seconds and you're not reaching your target temp, then there's an issue.

One could be the pressure switch and the other issue could be the temp probe inside the evaporator.

[George.]

Hi guys,

thanks for the replies. 
I will have to wait till summer to test properly, but it short cycles both when heating and cooling.

I’ve ordered a new internal temp sensor that sits under the vent in the steering wheel

also, GTSBOY, I have an Apexi FC ecu, I’m assuming I won’t be able to diagnose or would it still work? Could the ecu be causing the problem??

 

the pressure switch is quite cheap I will get a new one and try it out, hopefully it doesn’t require purging the refrigerant again?

[GTSBoy]

34 minutes ago, George. said:

also, GTSBOY, I have an Apexi FC ecu, I’m assuming I won’t be able to diagnose or would it still work? Could the ecu be causing the problem??

Putting the climate control CU into diagnostic mode is independent of the ECU. You just have to do the dance prescribed in the manual. No, I do not know what the dance is. I have an R32, so use the dance in the R32 manual.

On older cars, I would have said "no, the ECU should not affect whether the A/C works".... but for an R34 that might be wrong. I don't recall the detail, but there was extra mods required to make my R32 A/C work against the R34 ECU. The R34 ECU apparently gets involved in the running of the A/C more than earlier cars did. Theoretically, if the PFC is a true plug in, then it should just work the way that the original ECU does - wrt A/C. But there's always scope for them to have not cared.

37 minutes ago, George. said:

the pressure switch is quite cheap I will get a new one and try it out, hopefully it doesn’t require purging the refrigerant again?

Nope. Pressure switch out = getting the fridgey out to pump the gas out before pulling the switch. The switch really cannot sense gas pressure unless it is up against the gas.

[Dose Pipe Sutututu]

There's another sensor that sits inside the evaporator, that's a C U N T to get to, but can be done without removing the entire unit.

Usually it's not the sensor that dies but the actual capacitor in the circuit (part of the plug that dies).

 

[Dose Pipe Sutututu]

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