No heat from heater 1990 ZR1 - ZR-1 Net Registry Forums

jrd1990zr1 · 08-29-2017

Thoughts and suggestions please. AC works fine, no codes set, no fuses blown. I only get cold air from heater. Temp gauge never goes above half way. Had heat last fall, but not now. Does this sound like the heater core is air locked? Any thoughts and/or possible fixes are appreciated.

Thanks

-=Jeff=- · 08-29-2017

Have you checked coolant level? When was the T-Stat last changed?

if the car is not getting warm and the temp is showing cool, maybe the t-stat is stuck open

jrd1990zr1 · 08-29-2017

Jeff,

Coolant was a little low but not much. Not sure about the T-stat, I have not changed it.

Is it possible the coolant went low and I got an air bubble in the heater core?

Thanks, John

-=Jeff=- · 08-29-2017

possible, but I have a feeling it is either stuck T-Stat or maybe a clogged heater core

QB93Z · 08-30-2017

You can check the coolant flow to and from the heater core with a thermometer on the pipes in the right side of the engine bay.

The problem could also be a stuck Heater Blend Door. The Heater Blend Door is located between the heater core and the AC Evaporator in the AC Ventilation assembly. It is above the passenger side, lower dash panel.

You can see the Heater Blend Door by removing the AC Blower Control Module from the Ventilation duct in the engine bay, near the firewall, inboard of the coolant expansion tank.

With an assistant you can observe the operation of the Heater Blend Door by removing the AC Blower Control Module and looking in the hole with a flashlight. Turn the Ignition ON. Have your assistant change the AC/Heater thermostat on the dash from 60 degrees to 80 degrees then back to 60 degrees. The door should move. The engine does not need to be running to do this check.

Good luck,

Jim

jrd1990zr1 · 08-30-2017

Jim,

I see no movement of a door through the heater resistor hole. Top line to heater core is about the same as the metal crossover, however the return(lower) metal line from the heater core is significantly cooler.

I don't see anything in the 1990 FSM about getting to the door, door actuator or motor. Have you done this on your car? Am I missing something in the FSM?

Thanks again, John

-=Jeff=- · 08-30-2017

If I recall, the blend door motor might be Accessible by removing the glove box and glove box door. I know I can see the manual assembly from there.

I forgot about the Electronic blend door.. I have Manual AC which on my 90 I prefer

BigJohn · 08-30-2017

Glove box???

-=Jeff=- · 08-30-2017

A glove compartment or glovebox or glovie is a compartment built into the dashboard, located over the front-seat passenger's footwell in an automobile, often used for miscellaneous storage. The name derives from the original purpose of the compartment, to store gloves. They were sometimes in a box on the floorboard near the driver, hence the alternate moniker of a "glovebox". In most vehicles, the glove compartment closes with a latch, with the option of being locked with a key (often desirable when using valet service, or when parking while the convertible top is down, or when the compartment contains a mechanism to open the trunk).

Yes those of us with 90-93 cars had that privilege of a glove box..

-=Jeff=- · 08-30-2017

BigJohn..

here is a picture to help you

08-29-2017	#1
jrd1990zr1 Join Date: Dec 2005 Location: Delanson, NY Posts: 910	No heat from heater 1990 ZR1 Thoughts and suggestions please. AC works fine, no codes set, no fuses blown. I only get cold air from heater. Temp gauge never goes above half way. Had heat last fall, but not now. Does this sound like the heater core is air locked? Any thoughts and/or possible fixes are appreciated. Thanks __________________ 1968 convertible Lemans Blue, 1986 coupe Medium Blue NCRS Top Flight (sold), 1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold), 1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018, 2003 Anniversary Red Convertible (sold)

08-29-2017	#2
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,146	Re: No heat from heater 1990 ZR1 Have you checked coolant level? When was the T-Stat last changed? if the car is not getting warm and the temp is showing cool, maybe the t-stat is stuck open __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

08-29-2017	#3
jrd1990zr1 Join Date: Dec 2005 Location: Delanson, NY Posts: 910	Re: No heat from heater 1990 ZR1 Jeff, Coolant was a little low but not much. Not sure about the T-stat, I have not changed it. Is it possible the coolant went low and I got an air bubble in the heater core? Thanks, John __________________ 1968 convertible Lemans Blue, 1986 coupe Medium Blue NCRS Top Flight (sold), 1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold), 1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018, 2003 Anniversary Red Convertible (sold)

08-29-2017	#4
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,146	Re: No heat from heater 1990 ZR1 possible, but I have a feeling it is either stuck T-Stat or maybe a clogged heater core __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

08-30-2017	#5
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,687	Re: No heat from heater 1990 ZR1 You can check the coolant flow to and from the heater core with a thermometer on the pipes in the right side of the engine bay. The problem could also be a stuck Heater Blend Door. The Heater Blend Door is located between the heater core and the AC Evaporator in the AC Ventilation assembly. It is above the passenger side, lower dash panel. You can see the Heater Blend Door by removing the AC Blower Control Module from the Ventilation duct in the engine bay, near the firewall, inboard of the coolant expansion tank. With an assistant you can observe the operation of the Heater Blend Door by removing the AC Blower Control Module and looking in the hole with a flashlight. Turn the Ignition ON. Have your assistant change the AC/Heater thermostat on the dash from 60 degrees to 80 degrees then back to 60 degrees. The door should move. The engine does not need to be running to do this check. Good luck, Jim __________________ If it isn't fun, you aren't doing it right! 1990 Black ZR-1 - sold 1993 Quasar Blue ZR-1 1994 Competition Yellow ZR-1 1995 Dark Purple ZR-1 Maryland State Coordinator WAZOO Member Last edited by QB93Z; 08-30-2017 at 07:17 AM.

08-30-2017	#6
jrd1990zr1 Join Date: Dec 2005 Location: Delanson, NY Posts: 910	Re: No heat from heater 1990 ZR1 Jim, I see no movement of a door through the heater resistor hole. Top line to heater core is about the same as the metal crossover, however the return(lower) metal line from the heater core is significantly cooler. I don't see anything in the 1990 FSM about getting to the door, door actuator or motor. Have you done this on your car? Am I missing something in the FSM? Thanks again, John __________________ 1968 convertible Lemans Blue, 1986 coupe Medium Blue NCRS Top Flight (sold), 1990 ZR1 #2529 Red NCRS Regional and National Top Flight (sold), 1990 ZR1 #2124 Charcoal Metallic NCRS Top Flight 2010 & 2018, 2003 Anniversary Red Convertible (sold) Last edited by jrd1990zr1; 08-30-2017 at 04:14 PM.

08-30-2017	#7
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,146	Re: No heat from heater 1990 ZR1 If I recall, the blend door motor might be Accessible by removing the glove box and glove box door. I know I can see the manual assembly from there. I forgot about the Electronic blend door.. I have Manual AC which on my 90 I prefer __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

08-30-2017	#8
BigJohn Join Date: Feb 2012 Location: Ledyard,CT Posts: 8,066	Re: No heat from heater 1990 ZR1 Glove box???

08-30-2017	#9
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,146	Re: No heat from heater 1990 ZR1 A glove compartment or glovebox or glovie is a compartment built into the dashboard, located over the front-seat passenger's footwell in an automobile, often used for miscellaneous storage. The name derives from the original purpose of the compartment, to store gloves. They were sometimes in a box on the floorboard near the driver, hence the alternate moniker of a "glovebox". In most vehicles, the glove compartment closes with a latch, with the option of being locked with a key (often desirable when using valet service, or when parking while the convertible top is down, or when the compartment contains a mechanism to open the trunk). Yes those of us with 90-93 cars had that privilege of a glove box.. __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

08-30-2017	#10
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,146	Re: No heat from heater 1990 ZR1 BigJohn.. here is a picture to help you __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978