AC compressor on and off and on and off

[91SS]

During the CV 19 lockdowns I had a new compressor fitted and the system obviously regassed. Been running for a while over summer. The A/C system works fine below 100-105 kmh but cuts in and out at 115kmh- then returns to normal operation when the speed drops to 105 kmh.

I suspect the ECU is cutting it in and out too early. My 1990 Gregory's Engine Management manual says for a VN the ECU should cut out the compressor above 98% throttle and above 5800 rpm. Mine,s cutting out the compressor well below these two parameters.

Anyone know of any sensors I should check that would cause the ECU to cut out the A/C compressor at low engine power settings?

Was it behaving this way with last compressor?

TPS and vacuum sensor would relate to ECU detection of full throttle or high revolution I'm thinking.

Also check for possible belt slippageat high revs which can be hard to detect, often happens due to seep from power steering pump front seal.

But try to remember performance with previous compressor.

 

[MikeC]

Thanks. I did have a small leak with the previous compressor and lost gas causing the AC to blow hot and cold at all speeds then fail completely. But when the system was fully gassed with the old compressor it worked at all speeds- so I guess there was no inbuilt power limiter in the ECU or control system.

Now the AC is consistently working OK below 100-105 kmh but blowing hot and cold at higher speeds.

You might have something here- "Also check for possible belt slippageat high revs which can be hard to detect, often happens due to seep from power steering pump front seal. " I recently replaced the PS pump after the previous pump destroyed itself due to a return hose blowing out.

I'll have a look at the AC drive belt.

 

[91SS]

Thanks. I did have a small leak with the previous compressor and lost gas causing the AC to blow hot and cold at all speeds then fail completely. But when the system was fully gassed with the old compressor it worked at all speeds- so I guess there was no inbuilt power limiter in the ECU or control system.

Now the AC is consistently working OK below 100-105 kmh but blowing hot and cold at higher speeds.

You might have something here- "Also check for possible belt slippageat high revs which can be hard to detect, often happens due to seep from power steering pump front seal. " I recently replaced the PS pump after the previous pump destroyed itself due to a return hose blowing out.

I'll have a look at the AC drive belt.

Forgot to add check idler bearing as these can add load and were a common fault.

The GM belt was meant to address slippage and was enhanced to be a toothed belt.

Also the low gas safety switch on side of accumulator can play up causing cut out on sensing low pressure. There are different types of these with lower values.

 

[MikeC]

Forgot to add check idler bearing as these can add load and were a common fault.

The GM belt was meant to address slippage and was enhanced to be a toothed belt.

Also the low gas safety switch on side of accumulator can play up causing cut out on sensing low pressure. There are different types of these with lower values.

Thanks. I plan to have a look at the belt and idler pulley over the weekend. The LP switch was supposed to be changed when it was converted to 134a but I'll have a look at it- it might be tripping at higher pressures that it should at high compressor flows.

 

[Skylarking]

Haven’t read through this thread but R12 isn’t available any more so I’d guess your system was converted to R134A at some stage, maybe a quality conversion, maybe not…

Such conversions requires a bit of effort as different low and high pressure access ports must be installed in the low pressure and high pressure lines and the system cleaned of all old mineral oil, seals changes, PAG oil used, etc, etc… Compressor change is helpful but not the be all and end all of a conversion… And as R134A is a lighter gas than R12, supposedly a lesser amount of R134A needs to be injected into the converted systems else they end up overcharged and the compressor can cut out due to overpressure. So your problem may be related to the charge level

In any case, cooling performance is still somewhat compromised on converted systems because of hardware sizing. Primarily you need a bigger condenser than that which is used for use in an R12 system. So shortcut conversions don’t always go well (if indeed that’s your problem)

https://www.techtownforum.com/knowledge-base/r12-to-r134a-conversion-chart-formula/

PS: Not sure when R134A will be retired and thus become harder/impossible to find but newer cars now run R1234fy so our VF’s will suffer the same fate as those older vehicles running R12 aircon systems

 

[MikeC]

Haven’t read through this thread but R12 isn’t available any more so I’d guess your system was converted to R134A at some stage, maybe a quality conversion, maybe not…

Such conversions requires a bit of effort as different low and high pressure access ports must be installed in the low pressure and high pressure lines and the system cleaned of all old mineral oil, seals changes, PAG oil used, etc, etc… Compressor change is helpful but not the be all and end all of a conversion… And as R134A is a lighter gas than R12, supposedly a lesser amount of R134A needs to be injected into the converted systems else they end up overcharged and the compressor can cut out due to overpressure. So your problem may be related to the charge level

In any case, cooling performance is still somewhat compromised on converted systems because of hardware sizing. Primarily you need a bigger condenser than that which is used for use in an R12 system. So shortcut conversions don’t always go well (if indeed that’s your problem)

https://www.techtownforum.com/knowledge-base/r12-to-r134a-conversion-chart-formula/

PS: Not sure when R134A will be retired and thus become harder/impossible to find but newer cars now run R1234fy so our VF’s will suffer the same fate as those older vehicles running R12 aircon systems

Thanks. Yep I was converted to 134a years ago. The blokes that recently replaced the compressor would have known what they are doing when they recharged/leak tested it but they have reused the old belt- to change the A/C belt on a VQ with a 304 you have to remove the front 2 belts and these take a bit of effort to retighten properly.

I'ts a real battle keeping these old cars running with changes to things like the petrol composition and refrigerant availability over the years.

But my Dad and I have had Holdens since the mid 1950's and I'm not going to change.

 

[Skylarking]

The blokes that recently replaced the compressor would have known what they are doing…

As is, in older cars they used to have ac service stickers within the engine bay that listed gas type and charge weight as well as ac oil type. Sadly they’ve gone the way of the dodo as have other service stickers.

As is, your older Holden should have an ac service sticker listing R12 and required gas weight and Jandakot, WA, 6164oil type… You’d expect the first chap that did the conversion would have placed another sticker that warns others of the upgraded ac system and it’s new gas, weight and oil requirements. Was such done?

You'd hope there was something to warn the next ac tech so he can do the service correctly. Sadly even within a sticker, techs don’t always know what they are doing or aren’t good at their trade

Mistakes also happen or the ac guy knows your system will kack itself with too much gas and you’ll be back for an unrelated and charged for fix (earning him more $$$)…

It may be worth asking the question about gas weights

 

[MikeC]

I had a 134a sticker on the filter/drier case once but that's long gone as these units are replaced. The A/C tech knows I'm running on 134a - he had to find a Sanden compressor to suit.

 

[Skylarking]

I had a 134a sticker on the filter/drier case once but that's long gone as these units are replaced. The A/C tech knows I'm running on 134a - he had to find a Sanden compressor to suit.

I thought an air conditioner label was a complience requirement and as such it shouldn’t be placed on a removable item like the filter/drier. It should be fixed to a non serviceable solid part of the vehicle so others can identify the ac system rpservice requirements.

As such, those doing conversions should have labels printed up and attached to the vehicle so that any subsequent owners can get their vehicle aircon serviced more easily and with accuracy. But this assumes the R12 to R134A conversion was done correctly and the gas weight correctly calculated for change in pipe length, condenser size and such …. without having to have all the calculations redone every time the system is serviced (unless some hardware such as condenser or compressor is changed which impacts gas weights and oil volumes, in which case the label data should be updates).

An example of an aircon label below

https://www.originalpartsgroup.com.au/genuine-holden-decal-engine-bay-air-conditioner-re~5824

So much for following year spirit of ac code of conduct or proper regulatory control It’s just a protection racket to stop melegally working on my own ac system

 

[MikeC]

I agree fully -" It’s just a protection racket to stop melegally working on my own ac system ". The industry jumped with glee when the airconditioning gas purchase restrictions were introduced.