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| | | Trouble with heat | Joined: Oct 2011 Posts: 69 journeyman | OP journeyman Joined: Oct 2011 Posts: 69 | Hey all,
I'm having some trouble with my heat in my 91 G20. The heat will cut out sometimes and blow full force other times. The first time it happened I checked the fuses and I guess messing with them got it working. Any suggestions where to look? I do have a coolant leak at the heater control valve. New heater core was put in Feb last year.
On a side note, my 98 cavalier does the same thing and hitting the dash (or a pothole) usually gets it going. I changed the blower motor and blower motor resistor but it still does the same thing. Any suggestions there too?
Thanks
Road trip! | | | Re: Trouble with heat | Joined: Sep 2009 Posts: 1,051 old hand | old hand Joined: Sep 2009 Posts: 1,051 | I just went through this on my 85, sometimes work, sometimes wouldn't. I found a lot of corrosion where the plug goes on the resistor. Gm placed them where any rain that runs in sits in this area. I replaced the resistor, which seemed to help but I ended up putting a new fan motor on it and cleaning my ground wire attachment point, haven't had any issues since. Mine is a no AC van, corrosion might not be an issue with AC vans as the resistor is in a different location.
'85 GMC Shorty '98 Suburban K2500 '98 Pontiac G8 GT '77 Pontiac Astre '95 Jeep Wrangler "I thought you weren't allowed to talk to guys with vans??"
| | | Re: Trouble with heat | Joined: Feb 2013 Posts: 52 journeyman | journeyman Joined: Feb 2013 Posts: 52 | The air ducts in your HVAC system are controlled by vacuum switches and actuators, as you slide the lever from one to the other you are simply opening one vacuum circuit and closing another, on your intake manifold threaded into a coolant passage or water crossover at the front of your manifold is a vacuum ported switch that is controlled by coolant temp, you will have manifold vacuum going into 1 side of the switch and lines coming off the other side that trace back through the firewall and into the HVAC system, that ported switch is kinda the brains of the whole operation, if it's not working correctly nothing in the HVAC system will work correctly, also keep in mind that the only time you have manifold is at idle or steady-state cruise, when the engine is under load you will have no vacuum and all those air doors behind the dash go funky until you let of the gas.. hope this helps | | |
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