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Discussion Starter · #1 ·
The double fan in my engine bay for my aircon is not running, the AC has been regassed and pressure tested last week. It runs coolish when running down the motorway, but it’s warm when stationary or just started...only noticed it since the weather has warmed up a bit recently

Could anyone give me some pointers on what to look for or test?
 

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While I am new to this forum I am very familiar with AC especially in old Mercedes. But that is another conversation on another forum. The fan should run when the compressor is on as it should be cooling the condenser. I would test the fan with 12 volts to ensure it works. The fan switch is on the dryer and you can test to see if it works with the compressor on. If it is coolish on the motorway yet warm stationary something is not right. Even driving at speed will create enough airflow to change the state of the gas and it should feel cold. Measuring the temp of the outside air versus the temp at the vents with the AC will help you understand how well the system is working.

How long did it hold a vacuum before if was pressurized? Some people claim 30-60 minutes at vacuum. I tend to leave it for 120+ minutes. There is a chart somewhere that tells you the weight needed a full system charge.
 

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While I am new to this forum I am very familiar with AC especially in old Mercedes. But that is another conversation on another forum. The fan should run when the compressor is on as it should be cooling the condenser. I would test the fan with 12 volts to ensure it works. The fan switch is on the dryer and you can test to see if it works with the compressor on. If it is coolish on the motorway yet warm stationary something is not right. Even driving at speed will create enough airflow to change the state of the gas and it should feel cold. Measuring the temp of the outside air versus the temp at the vents with the AC will help you understand how well the system is working.

How long did it hold a vacuum before if was pressurized? Some people claim 30-60 minutes at vacuum. I tend to leave it for 120+ minutes. There is a chart somewhere that tells you the weight needed a full system charge.
Agree with Dug wholeheartedly.
"Most" AC guys really don't know what they are doing.
 

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At least the question of propane (R290) did not enter into the conversation. That one always get people going in the older car forums as a substitute for R12. AC systems are quite simple yet such a royal pain to trouble shoot. I am rebuilding a Denso AC 10p compressor.
 

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Discussion Starter · #5 ·
While I am new to this forum I am very familiar with AC especially in old Mercedes. But that is another conversation on another forum. The fan should run when the compressor is on as it should be cooling the condenser. I would test the fan with 12 volts to ensure it works. The fan switch is on the dryer and you can test to see if it works with the compressor on. If it is coolish on the motorway yet warm stationary something is not right. Even driving at speed will create enough airflow to change the state of the gas and it should feel cold. Measuring the temp of the outside air versus the temp at the vents with the AC will help you understand how well the system is working.

How long did it hold a vacuum before if was pressurized? Some people claim 30-60 minutes at vacuum. I tend to leave it for 120+ minutes. There is a chart somewhere that tells you the weight needed a full system charge.
Thanks Dug,
The guy had it under pressure for about 15 mins. He pressurised it with nitrogen, then he did a Vac test. The gauge didn’t budge.

can I jumper the fan switch on the drier with the system running? I’ve tested the fan relay pack and that works. I’ve also tested the fans separately directly to 12v and know they work too.

I was actually surprised when it was leak free, I was expecting to need to replace something. When it was running I get an odd whine from the system, which I’m assuming is from the compressor because it doesn’t do it when the ac is off. Maybe my compressor is bad??
 

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If the correct weight was added then you can eliminate the lack of gas. Yes, you can jump the switch to test the system. If you suspect the compressor is not working properly the system should be about 25 to 30 psi on the low side (usually the blue cap) and 200 to 250 psi on the high side (red cap). I would check the belt tension just to ensure it is not that. Ultimately, it could be the compressor. Which you could just replace. If one is to it properly the system should be flushed to remove any small bits of metal that could have be injected by the compressor. Some people claim the expansion valve and the dryer should be replaced as they are relatively low cost and a good time to do it. The dryer I would replace, the expansion valve is probably in a terrible spot.
 

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Discussion Starter · #7 ·
Thanks Dug,

I’ll check that fan and the belt tension in the morning.

I’ve just checked WIS and the expansion valve replacement doesn’t look too bad. If I have to break into the system to fix this problem I’ll put a new one in.

The technician added dye to the system but also said that the condenser wasn’t in great shape with it being original, however there weren’t any leaks when I checked it the other night with the UV torch and goggles. I’m more concerned that it could be the part you can’t see...the evaporator. I’m hoping that a leak from that component is rare?!

so if I have to break into the system I’d replace the drier, expansion valve, condenser and possibly the pressure switch as preventative maintenance and then whatever else is broken...which doesn’t leave much lol
 

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I was going to ask about the dye. Evaporators tend to be stable as they are not exposed to salt like condensers. Some dryers have all the switches included others you have buy by the piece. Your choice, but I tend to go with a close to OEM as financially possible. While I am not familiar with AC compressors used in Saab's, I know if it is a Denso unit to check the front around the clutch as they tend to leak from the front shaft seal. Given the spinning motion it can throw the dye everywhere and make it hard to spot. Also, look away from the system to where the dye could land and track back to the source. Sometimes a torch is too focused and a black light florescent fixture works better.

Make sure the technician flushes (not with water) the system as this is really important.

One trick I use in detecting a leak in the cabin is to run the AC full and not be in the car. Then get in and smell. I can smell a leak in interiors. I know the gas and lubricating oil is "odourless" but to me it has an odd smell that is not very pleasant.
 

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Discussion Starter · #9 ·
Thanks Dug. I’ve had to put this on the back burner for a few days due to my clutch master cylinder failing. Currently waiting for the replacement. I’ll update when I have the chance to investigate more :)
 

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Discussion Starter · #11 · (Edited)
Finally got back to this issue after having a nightmare with the clutch and every other part connected to it!

I got it connected to a tech2 and have the following info with the engine running:

Ignition key position: ON
Button Pressed: OFF
A/C Pressure: 1.8 Bar
Ambient temperature: 10.5 degrees Celsius
A/C Request: ON
A/C Relay: OFF



Is this pressure normal for a system where the compressor is not running?
 

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Discussion Starter · #12 ·
Finally got round to checking it with a gauge. Minimal pressure on the low side. Zero on the high side. Compressor is no longer running so clearly have a leak somewhere. Will get the UV torch out tonight for an inspection

 
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