sort of OT - car Aircon

Is the blower motor working? If it appears not to work at the lower settings does it actually still work on the highest setting.

Two obvious questions:

2) Does the car's temperature gauge get up to normal after a few miles of driving?

nib

I've always understood that the heating and aircon were independent. You can have the aircon on full and the heating on full at the same time - the aircon just removes water from the incoming air before the heater warms it up. It's the way to get the screen demisted in winter before the engine has warmed up enough to heat the air.

BICBW. Perhaps cars with climate control do it a different way.

They're normally separate: heater uses cooling water from the engine, aircon uses refrigerant with a compressor. They come together in the dash - air gets blown over a heater matrix (heat exchanger) and the aircon evaporator.

Climate control may lock them out so you don't run both together, but the systems are both there, you just can't open both concurrently. You have a single temperature knob rather than a flap to open the heater matrix and a button to connect the aircon compressor clutch to the engine belt and it controls which is enabled when.

On EVs it's either the same arrangement with a resistive heater instead of using engine coolant, or they use the aircon in reverse as a heat pump.

Theo

The fan works, but it blows neither hot nor cold, just air at air temp. TW

The fan works. There is no temperature gauge, only an overheating light which doesn't come on.

Tim W

Yes. that's what I thought. But wondered if possibly they came together elsewhere on this motor, eg one set of pipes to the dash only. TW

I have the same understanding as Theo.

The aircon is normally powered via a compressor that likely runs off the alt belt. Might be as simple as a fuse.. Depending how long it's been it might need a regas, but if the compressor is bust or the lines have corroded over time then that might not be an economical fix, as I found out on my last car.

The heater element is separate and heated by the engine's cooling system. Air from the blower is diverted across the matrix and as the engine warms up it warms the air. I think I'm right in saying that the coolant always circulates across this matrix but when the engine thermostat opens at around 90degrees it also flows into the radiator at the front of the car. If the blower works but there's no heat even when the engine is up to temp it suggests a blockage. You might be able to clear it with a coolant flush. When was the coolant last changed?

As you don't have cold or hot, it could also be the diverter that redirects the air across the relevant matrix is broken. Depending on the age and spec of car they will be either mechanical or motorised.

My, then 14yo, Mitsubishi Space Star needed regassing. Local garage did it. Cost ~£35 a couple of years ago. Worked perfectly until I sold it when it was 19yo. May be going still.

From my playing and experience, the two most likely reasons for air-con not working are broken drive belt on the compressor or gas all leaked out. Maybe also an electrical fault on the clutch that takes it in or out of service.

The two most likely reasons for heating not working are a stuck flap controlling whether the air goes via the heater matrix or not (had that on a Citroen ZX) or engine not getting up to temperature, such as a stuck-open thermostat (had that on a Mazda 323).

There's not much that affects both.

I don't think there's always air diversion around the air-con evaporator, it behaves as it it's always in flow and if you don't want full air-con you either have a 2-speed compressor (like my Smart) or you just blend in some hot air from the heater.

Most likely two separate faults?

nib

and a blocked heater matrix. I had that on my Cortina IV.

Feel the top hose, on the radiator, after a decent run - is it hot?

Sounds like the ‘flaps’ which direct the air in path required aren’t moving.

In older cars, these are linked to the controls via levers and mechanical cable links. In modern ones, switches and motors do the job.

What happens when the OP presses the air-recirculation button ?. This must have an electro-magnetic connection to a flap somewhere and it should be possible to hear this.

THis being uk.d-i-y, doesn't everyone have a hand-held laser temperature measuring device ?.

The two pipes that supply the heater should be easy to identify at the back of the engine bay, going through the bulkhead, but I seem to recollect that on my 1998 Astra F, there was also a temperature-controlled valve that turned this loop off when the temp was above a certian level, presumably because you didn't need hot water circulating into the heater block when the heater was not required.

Something else to check for

Also, on modern ICE vehicles the circulation to the heater matrix (radiator) may be delayed until engine has reached its full operating temperature.

No.

Do you have a cat ?.

Lots of fun getting mog to chase the red spot around the wall.

Also handy for measuring temperatures :-)

It sounds like you probably have more than one issue...

Assuming that the heater part is "conventional" then there should be a hot water feed and return to the heater matrix. This is what should heat the air (either ram fed or fan fed) into the cabin. It is not unknown for the heater matrix to be "bypassed" if it springs a leak (since they are often well embedded in the dash and can be a PITA to replace). Also check there is enough water in the radiator. On some cars there may be additional valves / stats to inhibit flow through the matrix until the engine is up to temp.

After the heater matrix, the air should pass through the aircon heat exchanger. When the aircon is switched on you should hear / see some activity as the compressor belt is engaged. (some systems also have a sight glass where you can see if the cooling gas/ liquid is being circulated). If working normally it will automatically cut in and out as it maintains the required level of cooling. If the gas level is low, it may run continuously and not actually cool much or at all. If the gas level is *very* low it may not even fire up at all. The fix for both it to get it re-gassed. They will normally assess if for leaks at the same time, and add the right amount of lubricant to the gas as well.