2008 GrandPrix no heat/no ac - has coolant and refrigerant what could be wrong?

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Asked by Jun 01, 2015 at 05:11 PM about the 2008 Pontiac Grand Prix Base

Question type: Maintenance & Repair

It started last year, I checked the refrigerant and it's full. This past weekend I checked the coolant an it's to the top of the cap. I Google the issues and a lot of people out there seem to be having the same issue some say the ignition switch some say the relays I have checked them. I can hear the blower inside the car and it seems to work well. Does anyone have any other ideas?

19 Answers

18,170

You say you can hear it blowing but can you feel it blowing out of the vents ?

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Air blows out of all vents and to the appropriate position on the temperature control switch.

18,170

Sounds like you have a bad temperature control switch. It's not controlling the door in the heater box that opens and closes switching from heat to A.C.

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You miss understood me, the control switch control is working fine. If you switch to the defrost position it goes to the defrost and all other vents are switched off. The fan blows to the appropriate speed based on the fan speed position. I don't think it's the Temperature Controller. When it comes to the AC, the compressor is not coming on, when it comes to heat the hoses in the engine compartment are hot but it doesn't blow any hot air!!

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I'm currently looking at a print out of all the fuses and relays that are associated to the HVAC system and there are a couple more that I missed. I got a PDF copy of a repair manual it's not the same year but it's close enough.

18,170

If you read my last answer you will see I said temperature control switch same as temperature controller that switch not only controls that door in the heater box but it also controls the the A.C clutch coming on because it senses when you lower the temp.

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ok, even if it switches to defrost, to the vents, to your feet. I can hear the door making the switches and the air blowing out of the correct vent.

18,170

The main word I would like you to focus on is temperature not switch over switch that changes the air from defrost to vents they are to different switches.

40

Ha! Ok, so there are two items in one! Because it has a push button to manually turn on the AC or it will auto select based on temperature set on the controler. The AC light comes on if you lower the temperature below ambiant or if you manually press it either way the compressor doesn't come on.

18,170

I still say there is something wrong with that switch. To bad that it's a all

18,170

To bad that it's a all in one switch.

18,170

You may want check in a repair manual to see what it means when you lower your temp your A.C light comes on it may tell you exactly what's wrong or ask a mechanic at your GM dealer ship. Sometimes they are nice and will tell you what what your problem is. It may be something simple who knows with vehicles these days.

64,935

If you have automatic climate control the A/C compressor will run any time the outside temp is above 35°F . If you have a manual system the A/C compressor will run if the "A/C" button on the control panel is pressed and the outside temp is above 35°F. The compressor will also run whenever defrost or defog is selected on the control panel and the outside temp is above 35°F. I'm not sure exactly what the problem is with your heat and air-conditioning but I noticed that some of the information posted about the A/C compressor operation is wrong. HTH. -Jim

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Well this might be just me trying to explain the non operation of the HVAC. But it's simple set the temperature to let's say 60 and the fan is set to auto, the light bellow comes on showing the AC is supposed to kick on (compressor) but it doesn't. No cold air blows out the vents the engine RPM doesn't adjust for the extra load by the compressor coming on (which it doesn't) so to me it seems that the temperature controller and the AC automatic seems to be doing what it's supposed to. But since the compressor nor the fans come on well it just never produces cold air.

1 out of 1 people think this is helpful.
64,935

Now we're getting somewhere. If you're sure that you have a full charge of refrigerant the compressor should be coming on. But it's not. When the climate control system wants the compressor to run it sends an "a/c request signal" to the Body Control Module (BCM). The BCM will then start the compressor. Sounds like the low pressure cutoff switch is bad. The light on the dash is coming on so I'm assuming that the a/c request signal is being sent to the BCM. If the low pressure cut off switch is open (off) because of either low refrigerant or the switch is bad the compressor won't start and the engine won't speed up to compensate for the added load of the compressor. HTH. -Jim

1 out of 1 people think this is helpful.
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Ok, I was thinking of finding the low pressure switch and jumping it to get the compressor to fire up and check the line pressure. But what gets me is the heat it should be simple hot water in the hose, luke warm coming out the hose so I just don't get it.

1 out of 1 people think this is helpful.
64,935

It may be a twofold problem. We know for sure that the a/compressor isn't coming on. Now for the heat. You have an electric motor type device under the passenger's side of the dash which positions a door to give you hot air, cold air, or a mixture. But before we tear into the dash have you felt the heater hoses in the engine compartment near the firewall. Both should be hot when the car is at operating temperature. Hot enough that you can't hold on to them. If one or both is luke warm or cool the heater core is clogged. If both heater hoses are hot you know that coolant is circulating through the heater core. One thing to remember about automatic climate control is if the inside of the car is above 90°F the system won't go to heat. Once you're sure coolant is circulating through the heater core and the inside of the car is cool enough to get heat check the actuator under the dash that positions the temp door. If it's not working the air temp won't change no matter where you set the controls on the dash panel. HTH. -Jim

1 out of 1 people think this is helpful.
40

OK, that makes sense if it's too hot it shouldn't. OK, now on the clogged core is there an easy way to unclog it?

1 out of 1 people think this is helpful.
64,935

You can try cleaning the cooling system with a chemical cleaner that's designed for this. But something else (water pump, radiator, etc.) may spring a leak. Or you can disconnect the heater hoses and try flushing it out using a garden hose. But if that doesn't unclog it, then replace it. It's about a 3 hour job at a shop. HTH. -Jim

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