HVAC Diagnosis help please!

leeshephard · 19 Oct 2016

Hi

The AC on my car has never worked, and as I have a European trip booked next year I decided this was the year to get it working. I have replaced the Condenser, Evaporator, Expansion valve and dryer. I drained the old oil from the compressor and refilled with new PAG Oil.After flushing all the pipes and reassembling , I then pressured tested to 40 PSI and then deep vacuum for 3-4 hours and left it overnight. I then refilled by weight with 840g of R134a.

Ac now blows nice cold air! Well, sometimes....

Fault Description:
- Start car from cold engine (left overnight). AC Condenser fan runs, Compressor runs. Cold air at vents. ( I left the car running for over 30 mins and AC continued to work correctly)
- Stop car leave for a few mins (waited for CCU internal fan to stop) then started car. NO AC CONDENSER FAN AND NO COMPRESSOR RUNNING. CCU looks fine, all buttons lit up as normal but no cold air.
- Stop car and connect to CCU using scantool - no fault codes found.
- Repeated starts of the car with 20-30 mins yield same issue.
- If car left for a few hours AC will work as normal.

Starting settings:
- Car in garage on axle stands.
- Ambient temps around 18C
- CCU Fan speed on 4, Temp on blue dot, AC Max button On, Resirc Button On, both sliders left most.

Previous diagnostic checks performed:
- AC gas pressure checked with proper dual manifold gauges and is within spec in factory manual.
- Using the Rennlist/ToreB scantool connected to CCU and ran the test program. All fans and servos activate and run correctly.
- No fault codes stored in CCU

I am a bit stuck now! It seems to me to be an issue with the CCU, a dodgy transistor maybe?

Any help is gratefully received.

Cheers

Lee

ToreB · 19 Oct 2016

I guess you have a problem with the A/C switch in the CCU. These front panel switches sometimes are corroded inside, and a good quality electronics cleaning spray could fix this.
If you plan to remove the CCU front panel, please be aware that the switch caps are brittle and easily comes loose, as well as keep your fingers away from the very brittle temperature sensor in the vent opening.

When the compressor/condenser fan does not run, does it help to press the A/C button off and on again? It might be a good idea to give the switch a small excercise by pressing the button repeatedly to try to remove the corrosion.

I guess you have the 993 type CCU with two A/C buttons. Does the condenser fan/compressor start when using the other A/C button?

Cheers,
Tore

leeshephard · 19 Oct 2016

Thanks Tore, I was hoping you might answer

I have pressed the switches on and off a lot and wiggled them to see if the AC comes on - it does not :-( I guess it would be strange for both switches to not work? Should I go for the cleaning?

Zingari · 19 Oct 2016

Lee, I cant help but notice you have the same garage door as me plus they also sold it to you without the box casing. When I pointed out the risk of it not sealing flush at the top to prevent cold air getting in I was informed the casing is extra on internal fits and cannot be retrofitted without taking off the whole door/mechanism :bandit:

I've managed to 'adjust' it so I can just about prevent daylight gaps but the box casing would eliminate the issue :roll:

ToreB · 19 Oct 2016

This could be internal contact problem. I cannot see any external cause for shutting off both the condenser fan and the compressor outputs simultaneously. I presume all other functions works as normal when this happens.
The sandwich PCB construction inside is not easy to repair with a lasting results, maybe your CCU has been in for a service somewhere?
I can repair this and do a full test of your unit if you are interested. Shipping time to Oslo is 3-5 days. PM me if interested.
Cheers,
Tore

leeshephard · 20 Oct 2016

Zingari - Yes I also had that issue, although I was offered an enclosure at the time of purchase it was a few hundred quid more an I thought I could do without it. In hindsight it would have been better to have stumped up the extra cash. I tried to close the gap with a strip of thick neoprene tape at teh top of the door - it worked for a while but eventually the strips came off, you can see one hanging down in the picture!

Tore - Thanks for the response, I am reasonable at taking apart electronics so will have another look, you think I should we checking the front control panel pcb to check for correct switch function? When I last took the panel apart it did not look like anyone had repaired it in the past, all the solder joint were even and shiny etc. I've also PM's you regarding the repair.

Thanks again

Lee

leeshephard · 20 Oct 2016

Tore, do you know if a CCU schematic exists? The factory manual only shows the loom wiring.

leeshephard · 23 Oct 2016

ok going out of my mind here! This is a tricky issue!

Can anyone tell me if the output from scanntool should be like below in the attached image? I am not getting any changes in the variables highlighted in red - these just happen to be the AC functions...

Would really appreciate if someone could clarify what should be in these fields and weather I should see them change when I activate the AC switches.

Cheers!

leeshephard · 24 Oct 2016

Forgot to mention, my CCU is a 993.659.047.01

leeshephard · 23 Nov 2016

I Finally got my AC fixed!!!!!!!!!

I wanted to openly thank ToreB for his efforts on this and in particular highlight his in depth knowledge on our cars HVAC systems - I would have NEVER found the issue without his input. So - Thanks Tore you're a top bloke

If anyone is still reading and interested in the fix....

My issue was that the AC Condenser Fan and Compressor were only intermittently working. It seemed that if you started the car and it did not work it would stay that way until iginition off - If the car started and it happened to work it would continue to work again, until the ignition was off.

I checked all the wiring - ran through all the usual stuff, tested the CCU using Tore's ODB tool and it all tested OK. In the end I diagnosed that the CCU itself was not working so sent it to Tore to check. It came back as working perfectly :-( /

Tore then assisted me further with some info on the requirements of the CCU during cranking and suggested I check R33 in the fuse box which switches TERMX rail. Upon checking this relay with a multi meter I could see that it had power all the time that the ignition was turned on AND under cranking. After a quick google I suspected the ignition switch itself had so failed so disconnected the battery and buzzed it's connections - all worked fine, SOMETHING was putting 12V onto relay R33 under cranking. I then remembered my chavy Clifford Alarm that the PO had fitted in 2003 - it has a remote start option called 'Intellistart' which I never use. I eventually found the unit behind the drivers footwell cover stuffed behind the heater pipe and checked the wires. It had 3 switched accessory outputs that could be used to turn on the Heater and AC etc once the car is started and also kept power to them for 10mins after the ignition was switched off. ALL off these outputs were wired to the R33 relay input!!! Once I disconnected these outputs from the Intellistart module the R33 relay was not turned on under cranking! Hooray

My AC now works everytime exactly the way it should.

So...can anyone suggest an Alarm to replace the Clifford Concept 600 I have? Would installing a H&P be possible?

Thanks for reading if you got this far!

Lee

leeshephard · 23 Nov 2016

I Finally got my AC fixed!!!!!!!!!

I wanted to openly thank ToreB for his efforts on this and in particular highlight his in depth knowledge on our cars HVAC systems - I would have NEVER found the issue without his input. So - Thanks Tore you're a top bloke

If anyone is still reading and interested in the fix....

My issue was that the AC Condenser Fan and Compressor were only intermittently working. It seemed that if you started the car and it did not work it would stay that way until iginition off - If the car started and it happened to work it would continue to work again, until the ignition was off.

I checked all the wiring - ran through all the usual stuff, tested the CCU using Tore's ODB tool and it all tested OK. In the end I diagnosed that the CCU itself was not working so sent it to Tore to check. It came back as working perfectly :-( /

Tore then assisted me further with some info on the requirements of the CCU during cranking and suggested I check R33 in the fuse box which switches TERMX rail. Upon checking this relay with a multi meter I could see that it had power all the time that the ignition was turned on AND under cranking. After a quick google I suspected the ignition switch itself had so failed so disconnected the battery and buzzed it's connections - all worked fine, SOMETHING was putting 12V onto relay R33 under cranking. I then remembered my chavy Clifford Alarm that the PO had fitted in 2003 - it has a remote start option called 'Intellistart' which I never use. I eventually found the unit behind the drivers footwell cover stuffed behind the heater pipe and checked the wires. It had 3 switched accessory outputs that could be used to turn on the Heater and AC etc once the car is started and also kept power to them for 10mins after the ignition was switched off. ALL off these outputs were wired to the R33 relay input!!! Once I disconnected these outputs from the Intellistart module the R33 relay was not turned on under cranking! Hooray

My AC now works everytime exactly the way it should.

So...can anyone suggest an Alarm to replace the Clifford Concept 600 I have? Would installing a H&P be possible?

Thanks for reading if you got this far!

Lee

madalaa · 23 Nov 2016

Excellent news! ......... and Tore B is a legend in his own life time ....... he has help so many of the 993 guys here on 911uk and is owed more than a few drinks.

ToreB · 23 Nov 2016

Thanks for the kind words guys. I'll collect my drinks next time I visit the UK.
It is really satisfying for me to solve problems, both for myself and others. It gives me much joy and I guess this is how an engineers mind works. At least mine!
Cheers,
Tore

Pretzel · 23 Nov 2016

Great result.

HVAC Diagnosis help please!

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