Aircon compressor switching off and on in short intervals

Jagger · Post by **Jagger** » 25 Dec 2018, 14:42

Hi,
my XC70 (2005) is giving following symptoms: aircon is cooling for 15min and suddenly it stops blowing cold air.
I have read all the posts about bread clip and cable tie trick. I can't get to the aircon to put cable ties in. Is there a trick? Should I take the wheel off?

Could not also something else be the problem?
Maybe some sensor? Where are the temp. sensors and can they be bridged, maybe?

Thanks!

crlande · Post by **crlande** » 25 Dec 2018, 17:50

cycling on and off quickly is usually a sign of low refrigerant.

Jagger · Post by **Jagger** » 25 Dec 2018, 22:08

Well, I've been to a place to check the refrigerant. The guy didn't even hook up his equipment! He said:"The pipe is ice cold! There is enough refrigerant in the system!"
He thinks it has something to do with a faulty sensor.
Is there anything I could try, related to a sensor?

Post by **precopster** » 25 Dec 2018, 22:30

The evaporator temp sensor should read fairly cold when gas is in the system. If it reads high such as in our 2002 XC70 the a/c will shut off early.....big job to replace it as far as I know. It may be a bad connection on the evap temp sensor connector so if it can be reached and cleaned that may get a more accurate reading.

The sensor's temperature reading can easily be seen in Vida. With a/c on it should read about 7-10 degC

Also is outside air temp reading on dashboard accurate? Another thing that can cause a problem is a blocked cabin temp sensor located on the CC panel just behind 3 small horizontal lines. Just behind this is a small fan designed to cool the sensing wire. That small fan's current reading can also be seen in Vida.

Vida is pretty essential for A/C diagnostics

A test light connected to the large grey connector on the compressor will tell you if the computer is telling the compressor to turn on. If the light comes on and you don't see the compressor front face turning you need the zip tie fix

Post by **chrism** » 26 Dec 2018, 07:36

Once the AC stops blowing cold will it start blowing cold again after a while or do you have to shut the AC off for a while before you can turn it back on and get get cold air again?
Also, when it stops blowing cold dies seem to you that the volume of air flow diminish?
With the mechanic finding the coolant line to be frosty it sounds like the evaporator is freezing up possibly due to a bad evaporator temp sensor. BTW, replacing that sensor is not particularly difficult.
Somewhere I had temp vs resistance values for that sensor. I’ll gave to see if I can locate it.......

Post by **precopster** » 26 Dec 2018, 15:04

I have icy lines to evaporator and a very high reading for evap temp such as 40degC so the above makes perfect sense. Have to look up access to that sensor on Vida if it's in there.
Does anyone know how to get to that sensor? Killing 2 birds here......

Jagger · Post by **Jagger** » 26 Dec 2018, 20:07

Hi, thanks for all your help. I have managed to put the cable ties into place. Today I am driving long distance, from which I will report how it went. Maybe I know more thereafter.
I took out the climate control and cleaned the thin wire behind the 3 slots. It was full of dust.
Let's see what it does. Unfortunately, I have no VIDA.

Jagger · Post by **Jagger** » 27 Dec 2018, 13:38

Hi everybody, today I was travelling from Johannesburg to the Blyde River Canyon, a 4.5 hour road trip through an african summer at 35°C (95°F).
To my big surprise, the aircon was working fine all the way, although only set to 24°C. I can say: "I fixed it!", with all your help! Thank you!
I will watch it further, as we are going to the Kruger Nationalpark, expexting plus 40°C (104°F).

Jagger · Post by **Jagger** » 27 Dec 2018, 22:44

Quote from previous post:
<<Also is outside air temp reading on dashboard accurate? Another thing that can cause a problem is a blocked cabin temp sensor located on the CC panel just behind 3 small horizontal lines. Just behind this is a small fan designed to cool the sensing wire. That small fan's current reading can also be seen in Vida.>>

I just want to add something. In my opinion, the small fan behind the 3 small horizontal slots, is sucking in cabin air so that the thin sensing wire can measure the cabin air temperature. I don't think the fan is there to cool the wire.
I my case there was quite some dust and fly around that wire, which I scraped off with a very small knife and blew it out.

Jagger · Post by **Jagger** » 09 Jan 2019, 03:58

A final word on the aircon problem I had. Even at outside temperatures of over 40°C (104°F), there was no further problems with my aircon.
By now, I think that the switching on and off (of the aircon compressor) in short intervals does not really indicate a problem, as mine is still doing it in idling when I can check with the bonnet open or from inside the cabin by listening.
What it does when I'm driving, I don't know.