1996 Pontiac Firebird No Heat or Defrost

Tiny
MCHUSTON
  • MEMBER
  • 1996 PONTIAC FIREBIRD
  • 6 CYL
  • 2WD
  • MANUAL
  • 96,000 MILES
All functions work on the interior control switches, the fan blows, and I can hear the vacuum system engage when I switch the air conditioner/heater on - but there is no hot air - heater or defroster. I pulled the control knob unit out enough to be able to actuate the temperature control cable manually - but still no heat. Is there a heater control valve that stops and starts the flow through the heater core? No one seems to know what shuts off the flow, or whether it continuously runs through the heater core. (That doesn't make sense to me.) It seems to me that no water/coolant is making it to the heater core. Any ideas?
Thursday, August 14th, 2008 AT 5:08 PM

3 Replies

Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
I can t find a heater control valve in my locator, so it may not have one. See if both heater hoses get hot when engine is warmed up. Does the engine run at normal temp? Those cars used "dexcool" coolant which was known to plug up th ecooling system. If only 1 hose is hot or only warm, the heater core may be plugged up. WHen you turn on defrost, it turns on the a/c, so just use heater settings to figure this out
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Friday, August 15th, 2008 AT 7:23 AM
Tiny
MCHUSTON
  • MEMBER
  • 2 POSTS
Both lines going through the firewall to the heater core feel cool. After replacing a bad water pump, the car has run slightly warmer than it had, still just under 210 degrees, and that only at an extended idle. Does water/coolant flow continuously through the heater core, regardless of the setting on the instrument panel?
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Friday, August 15th, 2008 AT 12:38 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
According to my software it does. If you dont see a valve on the heater hoses in the engine compartment, there isnt one and it is a constant flow system. Sounds like the heater core is plugged up and isnt letting coolant flow through it. Be careful if you try to flush it yourself, too much psi will blow out the heater core, and that one is a bear to change, the cooling system only gets up to about 15 psi or so.
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Friday, August 15th, 2008 AT 3:27 PM

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