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Hey folks,
My AC ran great all winter long (rimshot!), but now it's getting rather intermittent. This isn't the problem where the vents aren't opening right. There's plenty of air blowing where it should, but sometimes in the heat of the day it stops blowing cold. I'll start up and it will cool the car down. Then 5 minutes later, it's blowing-outdoor temp air. So I'll turn the AC off for a few minutes. Turn it back on, and it's cold again for 4 or 5 minutes, then it goes back.
This happens mostly during the middle of the day. Once things start to cool off (less than 80 degrees, it runs normally). Any ideas?
Thanks in advance
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This is exactly what is happening to my 97 965. I'm glad you asked the question before me and received all these great replies.
Let us (me) know what you did and if it worked!
--
1991 745 & 1993 965 /// RIP: 86 764T; 79 262C
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Alright, let's see how many red herrings I can serve up here. This is everything I saw today with the car idling, thermostat set at 68 degrees, windows open, about 90 degrees ambient temp:
* Hot air blows out of the vents
* compressor cycles ~8 seconds on, then ~8 seconds off
* I hooked up one of those cheap pressure testers that you get with a can of freon, and it was reading off the charts (granted, it may have been a POS)
I'm taking the car to a specialist, so place your bets.
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No red herrings there. What cycling time do you get and what temps are you getting at the dash vent after car is running at 1500 to 2000 rpm for a few minutes?
You did not mention this cycling before. How were the low side pressures off the guage, too high? too low?
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David Hunter
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The short cycling often means low freon. The guage connects only to the low side. Low side pressure can aid in knowing the problem and help when adding freon
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David Hunter
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The temp doesn't go anywhere lower than ambiant unless I get on the highway (constant 2500 rpm). No idea what the low side pressure is (I've only got one of those cheesy guages that hooks up to the high side between the car and a $5 can of freon). I wasn't paying attention to the status of the electric fan, but the engine idled for about 10 minutes and didn't overheat, so there must be some cooling happening there.
Any sage advice?
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Those can gauges hook up to the low side, there's no high pressure port on these cars. It would be nice to know what the pressure range was when the compressor was cycling.
DEWFPO
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1998 S90 083,228 and 1995 964 154,100
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Is there really no High side? They hooked up the low side by the firewall, but could not find the high side.
At idle with the compressor running, it was between 35-50 psi. They added some freon, and it got better, but they were not comfortable adding any more without seeing the high-side readings. I was going to pop over here tonight to to ask where the other port is hiding.
The mechanic said the secondary fan was not kicking on for the AC (just for engine temp), so that's why it blows warm at idle. On the highway, it blows nice and cold for about an hour, then it blows warm. If you turn it off for 5 mins and then start the AC with the fan switch set to a manual setting, it will blow cold again. But the moment you get to stop/go traffic, it gets warm again.
Does that sound like the pressure switch that's down by the radiator? If so, how do i bypass it?
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There's no high side on the 960/90 series, but it can be read with a Volvo Scan Tool.
At idle with the compressor on the low side system pressures should read between 25-45 psi.
The fan comes on when either the coolant temp is at a certain temperature or the pressure in the HVAC system reaches a certain pressure. When first turned on, the compressor will come and and few minutes later the fan should come on when the pressure reaches the preset psi.
The sensor down at the bottom of the condenser is the one that controls the fan speed for the HVAC operation.
DEWFPO
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1998 S90 083,228 and 1995 964 154,100
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Thank for the great info. Is that the pressure switch that's supposed to be bypassed? Because that fan is not kicking on at idle. And the system runs well at normal operating speeds as long as I don't turn on the recirc button (then it goes back to blowing hot, and I hav to turn the system off for a few minutes to reset).
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If the fan is not coming on when the pressure reaches it's set point, then the pressure sensor on the condenser is likely bad. That is, as long as the fan comes on normally the rest of the time. That would probably eliminate the fan motor or relay as potential problem areas.
DEWFPO
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1998 S90 083,228 and 1995 964 154,100
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yup, you described exactly what it's doing. the fan comes on for engine temp, but not for AC. I'll start looking for a new switch ASAP.
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Something else to check is the 2 speed cooling fan. If it isn't working properly the system will over pressure and cut out the compressor.
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I had a similar problem with our 95 960 and it was the A/C compressor overtemp safety sensor. It was a common problem and is easy to bypass. It seems the setting on these was too low and Volvo recommends the bypass.
That being said, on our 98 S90 the A/C would blow icicles out of the vents the first time the A/C was turned on for as long as the A/C would run no matter what the outside temps. Once the car was shut off, the A/C would not blow cold air again on hot restarts for the rest of the day regardless of outside temps. The next day it would blow icicles again on the first A/C use. This was corrected by adding a small amount of R134a to the system. It appears it was low. I would have never guessed that a low charge would cause such a strange HVAC system behaviour.
DEWFPO
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1998 S90 083,228 and 1995 964 154,100
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Does the compressor turn off? If so the heat cut out sensor at the compressor can cause that. I bypassed mine.
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David Hunter
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I can hear the compressor clicking on and off as it runs. But I'll check it to see if it's just staying off.
What is the heat cutout sensor? I've seen a lot of pressure sensors at FCP Groton's site, but they seem to deal with the condensor. Is that what you're talking about?
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There is an overheat switch in series with the wire to the compressor coil. It is mounted on the compressor itself.
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David Hunter
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or it could be the moisture in the ac system that is iced up ( blocked ) the expansion valve. This will turn the compressor off due to hi-pressure on the hi-side, then the ice will melt, then the ac will work again. The cycle will repeat, again and again ....
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Is there something that could cause moisture to build up? Where should I look?
Maybe the drain is not letting the moisture out fast enough? I don't have water flowing onto the carpet yet.
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I was talking about moisture inside the the system. If this was the case, you have to evacuate and recharge with a new receiver-drier.
If it was the case where the evaporator iced up, then your system may be low on freon, or the drain got clogged up.
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