P38 air con

[Datatek]

Good evening everyone,

I have the following question about my air conditioning system.
I had the air conditioning service done at a garage today. The air conditioning system was refilled. All good so far. But it still doesn't work perfectly.
The mechanic found that the compressor is constantly switching itself off and on again - i.e. not constantly - hence the lack of cooling. Further investigations are necessary...

What could it be? Does anyone know the problem? Thanks!

What year is your car? On later cars, there is a relay that operates the compressor clutch, it's relay 3, a smaller relay than the others, that would be my first thing to check. If it's an early car, the problem could be the HEVAC.
It could also be the dual pressure switch.

 

[pwood999]

Also did they put enough gas in it ? P38 needs 1200g which is a lot more than most modern cars..

 

[Datatek]

Also did they put enough gas in it ? P38 needs 1200g which is a lot more than most modern cars..

Mine will run with a good bit less than that, just doesn't get very cold but a good point.

 

[Datatek]

If your car has relay 3 fitted I can give you an easy test to check operation of the compressor clutch.

 

[Frank_38]

1380g R134a - they had a very professional device for this - they did a good job! If I understood everything correctly, everything was drained and then refilled. it took about 45 minutes...

I have a sticker on the front - everything is specified there.

I have the Range with Bosch...

the air conditioning is already cool, but not really cold. That's probably because the compressor doesn't run continuously.... that was the statement....

 

[MrGorsky]

I thought thats how it worked? On to raise pressure of the refridgerant, then off until the pressue drops again with use of refridgerant, then on again. The compressor doesn't run constantly with normal use I didn't think? I often hear mine click in and out when the engine is just ticking over when waiting in traffic for instance....

 

[Frank_38]

...of course that could be true, I can't judge whether the guys had a clue about the range...

 

[Datatek]

I thought thats how it worked? On to raise pressure of the refridgerant, then off until the pressue drops again with use of refridgerant, then on again. The compressor doesn't run constantly with normal use I didn't think? I often hear mine click in and out when the engine is just ticking over when waiting in traffic for instance....

Spot on young man

 

[Datatek]

...of course that could be true, I can't judge whether the guys had a clue about the range...

Could also be a blend motor problem if it's not getting cold. The aircon on the P38 is functionally no different to most other cars of the same vintage, no specific P38 knowledge needed when filling apart from the type and amount of gas.

 

[Mark Piercy]

I can say the compressor on mine doesn't run constantly or on Elliotts.
I'm not sure if it's designed that way as to not freeze one side of the system

 

[Datatek]

I can say the compressor on mine doesn't run constantly or on Elliotts.
I'm not sure if it's designed that way as to not freeze one side of the system

Aircon & fridge compressors never run continuously.

 

[pwood999]

Get a thermometer on the high & low side pipe & compare the temperature.

FYI, my little Merc C180 Coupe wasn't getting cold at idle, so checked the pressures at idle & 2500rpm. All looked ok, but the vents weren't as cold as expected. Then I jet-washed the condenser & cleared out loads of debris. Now it's nice & cold even at idle.

 

[Frank_38]

Get a thermometer on the high & low side pipe & compare the temperature.

FYI, my little Merc C180 Coupe wasn't getting cold at idle, so checked the pressures at idle & 2500rpm. All looked ok, but the vents weren't as cold as expected. Then I jet-washed the condenser & cleared out loads of debris. Now it's nice & cold even at idle.

Hello,

that's exactly it. They measured the temperature and thought that everything looked fine at first – the air is cooled but not ‘completely’ because then the compressor switches off – they mentioned something about 3 degrees – then it switches off or stops cooling.

 

[Datatek]

Hello,

that's exactly it. They measured the temperature and thought that everything looked fine at first – the air is cooled but not ‘completely’ because then the compressor switches off – they mentioned something about 3 degrees – then it switches off or stops cooling.

If it gets down to 3 degrees at the vents, it's doing well, the compressor is supposed to switch off or the pressure in the system would become too great, look at the diagram I posted
There are a few sensors that affect the operation, do you have any diagnostics?

 

[pwood999]

Nanocom will show all the HEVAC sensors. The evaporator sensor is in the right side of the heater box & shows how cold that's getting. If it's below 6deg, that as above check the flaps are moving to the cold position.

The values of the other sensors can also make a difference to how the HEVAC behaves.

Aspirator - measures interior temp.
Heater Core - clips on one of the heater pipes.
Sun Sensor - in middle top of the dash.
Ambient - varies between year, but under front chassis ?

 

[pwood999]

Just been outside & checked mine. With HEVAC set to 16deg, the compressor engaged for 2-3 min & was getting cold air from the vents with a minute of starting. The compressor then cycled on & off roughly every 30-40 seconds.

It will also depend how warm or cool the air going into both the condenser & evaporator is, because both will affect the pressure change in the system.

 

[Frank_38]

Yes, I missed the last promotion (15%/20%). I'll order the Nanocom during the next promotion.