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AC compressor on and off and on and off

losh1971

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I had my evap replaced and it was expensive but was well worth the cost in the end. What I found was the evap was actually probably in ok shape but it was clogged up with hair, dirt, lint and leaves. I have an idea the VR one can be made to fit a VP/VQ by changing the external pipework and adding a TX valve. I think it also requires a slight mod to the HVAC box. I know I had a VP HVAC fitted into my VR ute, and I was told it could not be done but it can.
My box was trashed when the tech pulled it out and couldn't be used and I supplied him with VP HVAC as I needed a slightly different box to the common VR sedan one, it would seem that 94 VR ute HVAC is slightly different to a sedan one in that it only has one drain and one hole in the floor, whereas VR and VS sedans have two drains, one on each side of the hump.
 

VPRob

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The bonus you get out of pulling the dash out is the opportunity to clean out decades of accumulated rubbish all through the heater box and repair flaps, replace perished foam seals etc. You can spend a lot of time doing all that and the cost of getting a mechanic to do it would be considerably more than I think anyone would pay me for my VP. I wouldn't want to drive it if the aircon didn't operate though.
 

VPRob

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"how does the aircon guy diagnose the evaporator " I had the AC guy try his freon sniffer in the evaporator pan drain hose but it sensed nothing.
That's interesting! If there was no freon detected in the drain pan hose (didn't know they could do this) then it sounds like the evap was ok. Still could be the 0 rings under the plenum with the freon leaking into the insulation down the back of the firewall.
 

MikeC

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That's interesting! If there was no freon detected in the drain pan hose (didn't know they could do this) then it sounds like the evap was ok. Still could be the 0 rings under the plenum with the freon leaking into the insulation down the back of the firewall.
I'm hoping my evap is still OK and the leak is in those O rings.
At least if I go the whole hog and replace the evap I can reassemble the dash and drive the car to the AC tech knowing the only joints that may leak are accessible from outside of the dash.
 

HarryHoudini

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. I wouldn't want to drive it if the aircon didn't operate though.

Yes,i get uncomfortable just sitting it my old beast knowing the air is not working,its garaged and has no rust so this thread might get me motivated to fix it but the quote a few years back to do the air properly was $2000-2500 and it has a new(Ebay) compressor fitted....sigh....
 

91SS

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Often it's just the low side port valve leaking I think it's called and it's hard to test. The speed of the leak 3 months sounds too quick.
Throw a new one in just in case you might be lucky . Not an expert but they might leak under vibration or bumps.
 

VPRob

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"Often it's just the low side port valve leaking" from 91SS
I haven't heard of this valve. Where is it located?

Yes,i get uncomfortable just sitting it my old beast knowing the air is not working,its garaged and has no rust so this thread might get me motivated to fix it but the quote a few years back to do the air properly was $2000-2500 and it has a new(Ebay) compressor fitted....sigh....
Hey Harry, I'd replace those O rings and re-gas and see what happens. Good luck with it.
 

HarryHoudini

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Hey Harry, I'd replace those O rings and re-gas and see what happens. Good luck with it.

Yes Rob.,will do but apparently the system needs a flush,as i said the last Air Con guy said he had seen it all before and the Evaporator needs replacing but will try a different guy this time around.On that subject its amazing the number of specialist Air. Con. Business's have closed up here on the NSW North Coast.I had trouble finding someone to top up the gas on my VE for the coming Months.
 

MikeC

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Yes Rob.,will do but apparently the system needs a flush,as i said the last Air Con guy said he had seen it all before and the Evaporator needs replacing but will try a different guy this time around.On that subject its amazing the number of specialist Air. Con. Business's have closed up here on the NSW North Coast.I had trouble finding someone to top up the gas on my VE for the coming Months.
If your AC guy has a freon sniffer clean up access to the joint in the plenum get him to test it for leaks. Might have to add gas to do this but at least you will know if that joint leaks. The thought of removing and replacing the evaporator gives me the horrors.
 

MikeC

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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?
 
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