Odd heating problem

[sparks_190e]

At idle or crawling in traffic the heater in my car occasionally seems quite weak, but full on once over 10/15 mph. It's not quite so bad if the heated rear screen, lights and radio are switched off. Of course the heated rear screen is only used for the first few minutes of a journey. On a longer journey it usually sorts itself out. Other times it's absolutely fine. Could this be a knackered battery somehow? Car is a 1990 Mercedes 190e.

[sparks_190e]

Thanks all, just to clarify the blower fans are blowing as strong as ever, but at idle and crawling traffic the heat is much reduced, but the air output at max settings is unaffected.

When I took the car out at lunch, turning the fans off then on again at full blast seemed to make it produce more heat.

Edited by sparks_190e on Wednesday 11th December 15:47

[sparks_190e]

GreenV8S said:

You seem to be saying that the air volume flow rate is OK but the air comes out cool, but gets hotter (briefly) if you turn the fan off for a while.

That suggests you don't have enough coolant flow through the heater matrix. Perhaps it's blocked.

Perhaps it is, but then sometimes it works absolutely fine.