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Aircon Technical Help


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Hello

My first post and sadly its a problem.

I'm having trouble with the aircon on my 2004 IS300. Friday it was working fine. The car didn't get used all weekend until Sunday afternoon (which was hot). When I turned on the aircon it wasn't blowing out cold air. When the aircon is switched on the light lights up on the heater controls (it doesn't blink) but the magnetic clutch on the compressor is not engaging. The aircon has been used through the winter for demisting so it's not been sat idle over the winter period.

After reading a few things on line I tried the below -

  • Checked the aircon fuse by the drivers kick panel - fuse OK
  • Checked the aircon relay under the bonnet - Re-seated the relay = no difference so I changed it with another Denso relay with the same part number just to check but again no cool air. I swapped the relays back afterwards.
  • Magnetic clutch resistance measured from feed connector on compressor to the casing of the compressor - 3.4 ohms
  • Checked wiring down to compressor mag clutch from relay box - OK
  • Checked +ve feed to relay box - OK
  • Bridged a 12v +ve feed from the Battery direct to the compressor clutch terminal in the relay box - clutch engages and compressor spins BUT STILL no cool air in the car.
  • Checked the power feed to the relay coil - NO FEED.

So I'm wondering if the pressure in the system has dropped to the point where a sensor has detected 'low gas level' and now some module/control unit (climate control unit?) is blocking the power feed to the relay hence the compressor mag clutch not engaging. This is all a guess based on what I found above as I don't know how the system fully works just the basics.

I have no manual or wiring details so I'm trouble shooting blind here. Is there a PDF scan of the Lexus workshop manual anywhere online for the IS300?

I've read a lot about these Halfords cans but I'm going to give them a miss, however, I notice there is a filling point at the front of the engine with what looks like a sight glass next to it. Its the sort of thing you see on some batteries for an indication of the electrolyte 'health'. I'm guessing this gives a visual indication of the gas level/pressure, but what should it look like if the gas is fine? At the moment there is noting but a black hole!

Can anyone help me here before I let a Lexus dealer empty my wallet!

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Hello

My first post and sadly its a problem.

I'm having trouble with the aircon on my 2004 IS300. Friday it was working fine. The car didn't get used all weekend until Sunday afternoon (which was hot). When I turned on the aircon it wasn't blowing out cold air. When the aircon is switched on the light lights up on the heater controls (it doesn't blink) but the magnetic clutch on the compressor is not engaging. The aircon has been used through the winter for demisting so it's not been sat idle over the winter period.

After reading a few things on line I tried the below -

  • Checked the aircon fuse by the drivers kick panel - fuse OK
  • Checked the aircon relay under the bonnet - Re-seated the relay = no difference so I changed it with another Denso relay with the same part number just to check but again no cool air. I swapped the relays back afterwards.
  • Magnetic clutch resistance measured from feed connector on compressor to the casing of the compressor - 3.4 ohms
  • Checked wiring down to compressor mag clutch from relay box - OK
  • Checked +ve feed to relay box - OK
  • Bridged a 12v +ve feed from the battery direct to the compressor clutch terminal in the relay box - clutch engages and compressor spins BUT STILL no cool air in the car.
  • Checked the power feed to the relay coil - NO FEED.

So I'm wondering if the pressure in the system has dropped to the point where a sensor has detected 'low gas level' and now some module/control unit (climate control unit?) is blocking the power feed to the relay hence the compressor mag clutch not engaging. This is all a guess based on what I found above as I don't know how the system fully works just the basics.

I have no manual or wiring details so I'm trouble shooting blind here. Is there a PDF scan of the Lexus workshop manual anywhere online for the IS300?

I've read a lot about these Halfords cans but I'm going to give them a miss, however, I notice there is a filling point at the front of the engine with what looks like a sight glass next to it. Its the sort of thing you see on some batteries for an indication of the electrolyte 'health'. I'm guessing this gives a visual indication of the gas level/pressure, but what should it look like if the gas is fine? At the moment there is noting but a black hole!

Can anyone help me here before I let a Lexus dealer empty my wallet!

you need to be licenced to touch the a/c system take it to toyota for a a/c service (normally much cheaper than lexus we do it for £40)and that will flag any problems and saves you the greef...

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Thanks for the replies so far. I have no intention of using the Halfords product even if others have used it with succsess. I will most likely call in a mobile AC engineer or take the car to Toyota once I am certain of what is wrong. I don't want to pay someone else to diagnose the fault when I can do it myself.

I read another post about AC problems and it mentioned a trianry switch. Having never heard of this before (I did say I knew just the basics) I googled this and it looks like I may have been right, i.e. the refrigerant pressure has dropped and the trinary switch has shut the system down to protect itself from damage. So hopefully all I need is just a gas recharge. However, I'd still like to check the wiring from the dashboard switch through to the relay and the outputs from the trinary switch just to be sure that I don't have another issue that is causing my problem which could be resolved by simply swapping out a part or module.

As such I have two questions -

  1. On a healty AC system what should be seen in the sight glass next to the AC filling point at the front of the car? Assuming this gives an visual indication of gas pressure mine is showing nothing but a black dot/hole.
  2. Is there an online scan of the Lexus workshop manual so I can check the wiring to the relay and the outputs from the trinary switches?

Again any help would be greatly appreciated.

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Regards the sight glass, you should see the refrigerant flow.... When the compressor first engages, you will see liquid refrigerant and refrigerant vapour bubbles, as the systen stabilises, you should see only liquid with the odd bubble... if the system is empty or the compressor not engaged you will see little. It tells you little about pressure, for pressure you will need a set of manifold gauges reading both high and low sides of the system... Pressures vary depending on ambient temperature so the same ammount of refrigerant on one day may gige a different pressure on another day...

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