Air Con: heating intermittent

[snibs61]

New volvo owner with a problem with my 2000 s40 2000cc.
The problem is heater works intermittently. i can be driving for ten mins and heater work perfectly then next min blows cold, then some time later will start blowing hot again. I have noticed that some times when i switch ignition on there is a chatter from behind the dash. can any body help please.

[gatos]

Most probably your heater control panel. Either get a second hand replacement, or try this fix: http://forums.swedespeed.com/showthread.php?70699

[snibs61]

Thanks read a few of these problems all seem to be fan. my fan works perfectly it the temperature that keep changing. does control unit control temperature as well?

[RandomGuy]

Originally Posted by snibs61

Thanks read a few of these problems all seem to be fan. my fan works perfectly it the temperature that keep changing. does control unit control temperature as well?

I have this problem as well. Previously replaced Heater Control Unit with second hand part due to the fan having a mind of it's own. Fan is now ok, but temperature varies no matter what temperature is set

[snibs61]

Thank you yes that sounds like it did you find out what the problem was? i thing its a relay behind glove box as its intermittent dont know if theres one there though.

[michaeljkeane]

Hi There, I recently had an issue with my fan speed. When I would change the gauge the fan speed would speed up / slow down and it would do this randomly while driving. I took out the heater module, (There is plenty of info on how to do this. It is quite easy Take out Radio, flip off the pannel over the gauges, remove 3 screws from the radio mount, 2 at top and 1 at bottom. remove the additional 2 on the heater control module and disconnect the cables).

With a multimeter I tested the Potentiometer (round black components where the centre turns as you turn the guage - Called Carbon Potentiometers) for the fan speed. These are 2.5K ohm Potentiometer's.
I noticed the reading was all over the place as i moved the guage from off to full on. You should go from ~2.4k to 0.4k resistance as you change the dial. I compared it to the temperature control pot (the good one) and I got a gradual change in resistance. I realised it was an issue with the pot.

I went into Maplin and picked up a 2.5k potentiometer for €1.05 (page 845 of their manual as of 08/04/2014). It was a bit smaller than the one on the PCB so I had to do a bit of a work around. I cut the metal connections from the old pot and removed it. I paired down the plastic end of the guage so it would fit inside the smaller pot. I placed the pot onto the gauge end and soldered its connections to the old metal links. Put everything back and it works a treat! I reckon if you are having issues with the temperature then this is the same fix, its the pot. A very cheap and pretty easy thing to replace. Just said I would share.

[morrismen]

Could be a heater flow control sensor - these stick and then you get intermitent heating, either cold or normal. It shows up with a code if you have a scanner.

[pierremcalpine]

I would first try replacing your heater transistor. Cheap/easy fix.

http://www.volvoforums.org.uk/showthread.php?t=151801

My next step would be to re-solder the two connects on the potentiometer in the CCM that control the temp. That may sound difficult but it really isn't. Just take the panel out, take apart, locate the two solder points (which will be lined up with the spindle of the temp control knob) suck the old solder off and put some new stuff on. Those CCM's are notorious for bad solders. I too tried switching my ccm out for a used one and had the same problem. I returned the used unit and ended up resoldering the pots and all was good afterwards. More detailed instructions are out there on how to perform this task but happy to help if you need more tips.