Heat working on and off (auto, best, mechanics, heating)

[Giesela]

197 Blazer, my heat has started working intermmitently. I haven't figured out yet
whether there is some sort of pattern to when. It is just cool/cold air sometimes.
Once its cool it stys that way. I'm not sure but it seems to work ok when just
new started?

Wondering if there is some obvious cause.

Background. My mid dash blowers in particular didn't seem to be blowing.
There was a small hole in some vacuum line that I had fixed. Things still don't
blow all that well, that seems a little intermittent too, but too expensive to fix.
Anyway, that vacuum line fix was pretty easy and cheap, two mechanics
didn't know to check it though, a guy at auto zone told me about it.

So, thought I'd ask about the heater before I talk to a mechanic.

[WyoNewk]

I'm not an expert, but it sounds to me like you need a new thermostat. Cheap and easy fix if that's it.

[sunsprit]

from your description, there seems to be several things going on which can be affecting the "hot" output temp of the heater:

1) air direction control; ie, the vacuum system/controls which direct the airflow which can involve blend doors on this heater system to regulate the output temperature
2) the blower motor/fan not blowing consistently

and finally,

3) the actual hot water flow through the heater core needs to be consistent and at the right temp. Could be ... but very unlikely at this point ... a stuck open thermostat running the system too cold. A touch of the heater hoses underhood to check for hot water is a quick check for this ... I'll touch the hoses, but a infra-red heat gun tells me specific temps.

At this point, it's probably best to take the car to a shop and let them diagnose the problem(s) for you. Likely there's more than one single issue going on ....

[ukrkoz]

I'd start with checking coolant level. When it goes low just enough, car does not overheat but heating capacity falls down.

[Sydney123]

Heater control valve?