2000 Blazer Heater Problem

Went to turn on my heater the other day, and it's only blowing cold air. If I get going about 40 mph I start to get a little warm air, but never like it was before. Took it to a shop, and they did a "Complete Engine Cooling System" flush, and they said it would cover everything. Also got a new thermostat put on. Nothing changed, still cold air. What now?

Went to turn on my heater the other day, and it's only blowing cold air. If I get going about 40 mph I start to get a little warm air, but never like it was before. Took it to a shop, and they did a "Complete Engine Cooling System" flush, and they said it would cover everything. Also got a new thermostat put on. Nothing changed, still cold air. What now?

Automatic or standard heater controls?
Good vacume to controls if it is vacume operated?
Check heater controls for switching to defrost or full heat cold to hot.
Check heater hoses for being hot to the touch.
If not remove heater hoses and see if water will flow threw the heater core good.
A lot of them have problems with heater core pluging up.
Which just a cooling system flush does not help unless the heater core is flushed also.
Run water threw it or try blowing air threw it and sometimes reversing the heater hoses for a while will help flush it out.
Let us know what you find.
MT

It's standard heater controls. I asked the shop if they were going to flush the heater core, and he did say yes.

I'm extremely novice to this, exactly which hoses should I be checking for warmth?

It's standard heater controls. I asked the shop if they were going to flush the heater core, and he did say yes.

I'm extremely novice to this, exactly which hoses should I be checking for warmth?

On the firewall there is two rubber hoses 5/8 -3/4 in. going into it from engine.
If coolant is flowing threw the heater core good both will be hot .
One may be a little hotter than the other but hot to the touch.
Around engine tempture 195 degrees.
MT