Mark Piercy · Oct 2, 2023

So.... Plenty of new parts for the aircon system on my lads 38'.
Our resident tech master has checked and tested the hevac.
We checked the pressure in the system and was off the gauge!!!!
Personally I have no experience with aircon systems and I'm going to ask those who have more than me this question.. (and probably many more)....
What would cause high pressure in the system. I can only think that maybe the expansion valve has jammed but I'm not sure even at that.
Compressor new, mahle.
New rad,
New dryer also.

Datatek · Oct 2, 2023

Mark Piercy said:
So.... Plenty of new parts for the aircon system on my lads 38'.
Our resident tech master has checked and tested the hevac.
We checked the pressure in the system and was off the gauge!!!!
Personally I have no experience with aircon systems and I'm going to ask those who have more than me this question.. (and probably many more)....
What would cause high pressure in the system. I can only think that maybe the expansion valve has jammed but I'm not sure even at that.
Compressor new, mahle.
New rad,
New dryer also.

Was the engine idling when you checked the pressure?

Mark Piercy · Oct 2, 2023

Both static and idling. Pressure off the scale!!

Datatek · Oct 2, 2023

Mark Piercy said:
Both static and idling. Pressure off the scale!!

Should be high when the engine is not running but drop back when the engine is idling. That's all I know from my recharge kit. The aircon has stopped working on my RHD P38, engine off the pressure is off the scale, idling there is next to no pressure. This is on the big pipe.

Bix · Oct 2, 2023

Too much gas added? I've seen a car where the owner used one of those DIY top up kits. Pressure was higher the Snoop Dog. We pulled twice the amount of gas needed for his car.

Datatek · Oct 2, 2023

If you fitted a new compressor, has it got enough PAG oil? Is the clutch definitely engaging?

Mark Piercy · Oct 2, 2023

It runs fine for about five to ten minutes and then faults. I'm going to buy a dual gauge kit so we can check it more thoroughly.

Datatek · Oct 3, 2023

Mark Piercy said:
It runs fine for about five to ten minutes and then faults. I'm going to buy a dual gauge kit so we can check it more thoroughly.

Exactly what fault is recorded? Do you get the book symbol? Have you checked the matrix sensor?

pwood999 · Oct 3, 2023

with engine off the High & Low side should equalize after a while. It needs to be >> 35psi or the compressor will never engage, but should generally be around 65-75psi.

Then with engine running the low side should drop, and the high side rise. How much depends on the R134 temperature.

Remember the gas refill quantity is done by weight, not pressure. P38 needs about 1200grams, which is double most cars.

Mark Piercy · Oct 3, 2023

I'm going to buy a gauge set. The gauge I've got is off the scale but wasn't previously.
The book symbol does come on @Datatek , the only one fault recorded is " 39 aircon request".
All the sensors are reading various temps through the system.

pwood999 · Oct 3, 2023

Definitely worth getting a dual gauge set. Mine is an Amazon job, but works well & doesn't leak. This only issue with the cheaper sets is the gauge range is way to high for cars !! Nobody needs 800psi !!

Mark Piercy · Oct 3, 2023

I've looked at the Amazon ones but there's a lot crap about

Datatek · Oct 3, 2023

Mark Piercy said:
I'm going to buy a gauge set. The gauge I've got is off the scale but wasn't previously.
The book symbol does come on @Datatek , the only one fault recorded is " 39 aircon request".
All the sensors are reading various temps through the system.

If the book symbol comes on, it cannot be from the SSR that drives the aircon relay because I disabled the SSR fault output so there is something else at at fault. I do not know what the "aircon request" actually relates to but it could still be a fault in the HEVAC even though it worked on my car. See what you get when the pressures are sorted.

pwood999 · Oct 3, 2023

Datatek said:
If the book symbol comes on, it cannot be from the SSR that drives the aircon relay because I disabled the SSR fault output so there is something else at at fault. I do not know what the "aircon request" actually relates to but it could still be a fault in the HEVAC even though it worked on my car. See what you get when the pressures are sorted.

What's SSR ?

Nanocom docs say:
The AC Request & Grant are the HEVAC asking the engine ECU if it's ok to enable compressor based on factors like engine temperature, load, current acceleration etc.

RAVE says:
A/C Request - This signal is active low and sends a request to the
ECM to switch on the air–conditioning system.

A/C Grant - This signal is active low and sends a signal to the
HEVAC ECU to acknowledge the request signal and
that it is ready for the load to be switched on by the
HEVAC system.

Datatek · Oct 3, 2023

pwood999 said:
What's SSR ?

Nanocom docs say:
The AC Request & Grant are the HEVAC asking the engine ECU if it's ok to enable compressor based on factors like engine temperature, load, current acceleration etc.

RAVE says:
A/C Request - This signal is active low and sends a request to the
ECM to switch on the air–conditioning system.

A/C Grant - This signal is active low and sends a signal to the
HEVAC ECU to acknowledge the request signal and
that it is ready for the load to be switched on by the
HEVAC system.

SSR = solid state relay, the device that drives the aircon clutch.

From what you are saying, it sounds like the A/C grant from the EDC is missing or the HEVAC is not recognising it.

pwood999 · Oct 3, 2023

That's probably what the error 39 means ? Not sure.

Mark Piercy · Oct 3, 2023

Start it up and it works,
Turn it off and it faults,
Sometimes it'll fault by itself.
Gas pressure on the low side is too high, running and not running.
So when the gauges arrive I can check the balance across the system and go from there.
So , if worked in your car @Datatek then it has to be this system that has the issue.
If the valve (20yr old) has jammed that would explain high pressure on one side.
The valve and the evaporator are the only parts that are original in the car.

Datatek · Oct 3, 2023

Mark Piercy said:
Start it up and it works,
Turn it off and it faults,
Sometimes it'll fault by itself.
Gas pressure on the low side is too high, running and not running.
So when the gauges arrive I can check the balance across the system and go from there.
So , if worked in your car @Datatek then it has to be this system that has the issue.
If the valve (20yr old) has jammed that would explain high pressure on one side.
The valve and the evaporator are the only parts that are original in the car.

It worked on my car and would cycle on and off from the button with no problem. It was not for an extended period though, no more than 10 or 15 minutes although it ran on the bench for a lot longer but there were no sensors attached so there may still be a fault in the HEVAC.

Mark Piercy · Oct 3, 2023

Thanks Keith, I'll go on from the gauges when they arrive.

Datatek · Oct 3, 2023

Mark Piercy said:
Thanks Keith, I'll go on from the gauges when they arrive.

Expensive things sons! Not as bad a daughters though

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