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Recharging A/C... fan not coming on

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Recharging A/C... fan not coming on

Post by bmdubya1198 » Sat May 18, 2019 4:34 pm

I just replaced the valve core for the low pressure port, and now I'm trying to charge the A/C on my 2000 R. It doesn't seem like it was taking anything though. The can wasn't getting any lighter and nothing else was changing as I tried to charge it.
The compressor cycles on and off every few seconds, but it won't stay running. The fan isn't turning on at all. Is that because there isn't enough pressure in the A/C system? I know the fan should immediately turn on when the A/C is turned on. I know I had a code on VIDA for the high speed, but I don't remember exactly what it was for. The fan still works properly when the ECT sensor tells it to activate. Already swapped the fan relay, no change.

Man, I hate working on A/C systems...


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Re: Recharging A/C... fan not coming on

Post by MDK » Sat May 18, 2019 5:52 pm

So you changed the needle valve? Did you evacuate the the system?.. I don't really take anything for granted as people's skills are all over the page. The system has to be in a vacuum. .. usually 28/29 inches of vacuum is the most you'll get.In the old days... the 80's .. I'd put a vacuum pump on it and let it run over night to remove moisture and check to see if the gauges would move. If it stayed the same for 15 minutes.. I'd charge the system until the accumulator would start to sweat and the evaporator temperature was at 41degrees on a hot day. Those were the R12 days .. you know... but the science is still the same.



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Re: Recharging A/C... fan not coming on

Post by bmdubya1198 » Sat May 18, 2019 6:28 pm

MDK wrote:
Sat May 18, 2019 5:52 pm
So you changed the needle valve? Did you evacuate the the system?.. I don't really take anything for granted as people's skills are all over the page. The system has to be in a vacuum. .. usually 28/29 inches of vacuum is the most you'll get.In the old days... the 80's .. I'd put a vacuum pump on it and let it run over night to remove moisture and check to see if the gauges would move. If it stayed the same for 15 minutes.. I'd charge the system until the accumulator would start to sweat and the evaporator temperature was at 41degrees on a hot day. Those were the R12 days .. you know... but the science is still the same.
I have not applied vacuum, can I do that on the low pressure port? Information is so scattered I just don’t know. There isn’t a high pressure port on these cars.
But yes, I changed the valve in the low pressure port.


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Re: Recharging A/C... fan not coming on

Post by abscate » Sun May 19, 2019 4:52 am

You need to pump out the air from the low side port with a vacuum pump to get the system ready for charge.

Once you do that the first Can will go in easily and will trigger the pressure sensor to engage the compressor partially

Remember these cars cycle the compressor so it’s normal for them to turn off and on , and that is not indicator of low Freon.


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Re: Recharging A/C... fan not coming on

Post by callahanoffroad » Sun May 19, 2019 5:51 am

Your mechanic can pull the vacuum or you can do it yourself. Bc it's only a low side fill it can take time to charge. Make sure you're putting the correct weight of coolant into the system. So if it takes 14 oz of r134 and you only put 8oz in the system isn't going to engage. Remember that you're starting from scratch bc the system was evacuated. Too much r134 like 20 oz will not give enough expansion room and the system still won't work properly and won't get cold enough. The label is on the hood.

You basically need this to vacuum your AC system out.

https://www.amazon.com/F2C-3-5CFM-Vacuu ... 2633&psc=1

You cannot have any water in the system, hence why you need to vacuum it.


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Re: Recharging A/C... fan not coming on

Post by bmdubya1198 » Sun May 19, 2019 8:03 am

OK, that would make sense then. I'm going to go pick up a vacuum pump today and vacuum it. I was confused since I was pretty positive it needed to be vacuumed, but I wasn't sure how since this is a one-port system. That should get my cousin's A/C up and running in both of his P80s too!
As for the fan though.... is it because there isn't enough pressure in the system that it's not engaging? I believe it's connected to the A/C pressure switch, so it would make sense if that was the case.

I know it's supposed to cycle, but the compressor will turn on and off almost immediately every few seconds. The vents are blowing warm and the system is totally empty. It's been like this since I got the car.

Anyway, I'll see if I can get this going today and report back.


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Re: Recharging A/C... fan not coming on

Post by callahanoffroad » Sun May 19, 2019 8:22 am

If it's short cycling there's simply not enough r134 to compress. You can see it with a pressure gauge. The compressor will be off and the psi will read ~30lbs. Then the compressor will kick on and the pressure will drop when it gets too low ~15lbs it'll kick off. Then the coolant cycles again and begins to build pressure and the compressor kicks on again. Sounds me me like you very simply don't have enough r134 in there. Ac systems are fairly simple. Just a pain in the neck to charge them. Make sure you charge it fully and let it run for at least 15 minutes so it can all circulate properly. Volvo ac systems are s slow fill system so it can take a bit. I'd say this is a two beer job.


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Re: Recharging A/C... fan not coming on

Post by bmdubya1198 » Sun May 19, 2019 8:32 am

Yeah, I was pretty sure that's why it was cycling. Once I vacuum it I'm pretty sure it should take the refrigerant.


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Re: Recharging A/C... fan not coming on

Post by jimmy57 » Sun May 19, 2019 10:48 am

The fan runs due to sensed high side pressure. It will need to have something close to 1/2 of the refrigerant charge before the pressure would be high enough for ECM to run the fan.
That car has a pressure switch on the low side line behind the engine that is used for compressor clutch control. It will switch off compressor at 22-24 psi and when the pressure begins to equalize between high and low sides and low side goes up to 42-45 psi the switch closes and compressor clutch gets powered on again. When it is low the compressor suction draws down the low side in a few seconds and comp goes off. The system pressure equalizes and it switches back on quickly because gas equalizing happens faster than when there is a full charge and liquid would have to backflow through orifice.
When you are adding refrigerant with engine running or doing any a/c diagnosis you run engine at 1200 RPM or a little more. This is standard a/c service practice. All vent temps and all pressures you will find in any reference will assume you have system at a speed where compressor is at a speed where it works at its rated displacement. The other standard diagnostic settings are windows closed, fan at 3/4 speed, and recirculated air setting.
On a cycling clutch-orifice tube system with full charge the compressor will cycle when the car cools down. The temp of evaporator and the low side pressure that results at that temp will go into the lower 20 psi range and switch opens. If ambient temp is lower that happens much quicker. If than fan speed is low the heat being absorbed by refrigerant is less and compressor cycling occurs more readily.

Side note: The Volvos with expansion valve refrigerant systems can either cycle compressor (P2 except xc90 with V8 or 3.2 I6) or when fitted with variable displacement compressor, the compressor control valve is regulated to decrease refrigerant flow to increase evaporator temp when evap temp gets below target. On the variable compressor systems the compressor control valve will be regulated for increased refrigerant flow if evap temp gets above target temp. Expansion valve systems regulate refrigerant flow to try to match the heat load and the heat removal capacity. Due to low compressor pumping at idle, the compressor capacity was bumped up so it would be adequate at low eng speed. The cycling of compressor or compressor control valve regulation on these systems is to compensate for having effectively too much compressor and thus too great a capacity to freeze the evaporator at higher engine speed and when heat load on system is less..

Evacuating the system isn't going to make any noticeable difference in charging speed. It is to get the moisture out and to get the air out that can dilute the refrigerant a wee bit. The refrigerant needs to go in slow when it has to run to charge. Too much liquid going in washes away the oil from compressor and you can get too much liquid on top of pistons to be compressable and cause compressor failure.



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Re: Recharging A/C... fan not coming on

Post by bmdubya1198 » Sun May 19, 2019 7:26 pm

Great info, thanks!

I pulled vacuum on the system today, and after running it for 10 minutes, it was only at around 10 in-hg. Over the next 10 minutes, it slowly crept back up to 0. Seems I've got a leak.
I used the Harbor Freight vacuum pump that connects to an air compressor, but unfortunately my compressor wasn't able to maintain enough pressure to keep it running properly. I'll get a regular pump once I fix the leak. Although this could be a good excuse to finally upgrade my compressor... 17 gallons is way too small and it doesn't flow enough for anything I need it for.


1998 V70 GLT Black/Beige 193k
2000 V70R Venetian Red/Charcoal M56 Swapped 188k
2001 S60 2.4T Black/Black 230k
2007 XC90 V8 AWD Sport Titanium Grey/Black 155k
1998 S90- Silver/Gray 207k
1995 850 collection of parts... crushed... still have parts, PM if interested!
1988 744 Turbo M46 Beige Metallic/Beige 188k- Still kicking myself for getting rid of this one

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