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Username Post: A/C all of sudden blows hot air        (Topic#195357)
Jimmy Foxx 
Posts: 2

Reg: 07-30-08
07-30-08 06:17 PM - Post#1488845    

Well. A/C is blowing hot air. Driving home from work it was blowing nice cold air, then i just fell hot air. the A/C low pressure lines our cold, but not cold air.

any suggestions?

Senior Member
Posts: 8252
Loc: Maryland
Reg: 02-25-02
07-31-08 03:52 AM - Post#1488990    
    In response to Jimmy Foxx

What year & model truck?

Might be low on freon, bad pressure switch. Did the air stay hot or did it ever cool back down?

Welcome to the site

'99 Silverado (NBS)

Dedicated Member
Posts: 5332
Loc: Lake Superior-Michigan US...
Reg: 03-30-00
07-31-08 05:56 AM - Post#1489035    
    In response to Jimmy Foxx

Low Pressure Switch

My 2001 GMC would do this. It was still under warranty so I had the dealer check it out. Been over 6 yrs but I seem to recall it being a low pressure switch.

Prior to finding the bad switch I had a hard time convincing them it would go cold to warm in a heart beat. They sat in shop with motor running and it blew cold. I convinced the sm to take a ride with me and 5 miles down the road it went hot just like I said. He was convinced, it was 92° that day. I guess the vehicle movement is what make the switch short out.

When he showed me the bad switch you could see a greenish tint on the terminals. Never acted up again. They had to take one from a new truck on the lot as I was not willing to leave without the A/C fixed. It was either that or give me a loader.

2017 GMC Sierra Denali Ultimate 6.2L(420hp)/8-sp Z95
2016 Polaris RZR 900 EPS

Banned Member
Posts: 2868

Loc: Rural Illinois
Reg: 06-06-02
07-31-08 07:02 AM - Post#1489072    
    In response to elcamino

My Ferd work truck did this and they said it was the fan clutch. Im not to sure they were right since it still does it once in a while. I just figure its part of driving a ferd.

00 Yukon SLT XL 5.3
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Jimmy Foxx 
Posts: 2

Reg: 07-30-08
07-31-08 06:05 PM - Post#1489556    
    In response to DeLong

it doesn't cool down, i tried putting a shot of r-134a+. it;s a 99 silverado 4x4 standard. low pressure switch would turn the compressor on and off. down thing it;s that because i got cold low pressure lines. unless the switch controls the hvac. same with the clutch. either way im going to look into it. you never know

Posts: 4

Loc: Maine
Reg: 09-23-08
09-23-08 02:43 PM - Post#1527921    
    In response to Jimmy Foxx

I have a 2000 silverado that had a similar problem. I changed the thermostat but it didn't fix the problem. I had the heater core flushed and it's as good as new. There is a kit you can buy to do it yourself but I had my local mechanic do it for about $80. Hope this helps.

Posts: 4

Loc: Maine
Reg: 09-23-08
09-23-08 03:21 PM - Post#1527959    
    In response to kvet

Sorry, I gave bum info. I had the heater blowing cold air, that's why I had the heater core flushed. Sorry had a dislexic moment.

Posts: 33

Loc: Florida, USA
Reg: 10-20-04
09-24-08 12:04 PM - Post#1528568    
    In response to Jimmy Foxx

My 04 Sub does that on the drivers side occasionally, while the passenger side is still blowing ice cold. Check the door motor that regulates heated air to maintain temperature. Mine just gets confused, cycling the ac switch or temperature control works for me.

Merritt Island, FL
2004 Suburban
2000 Blazer

Posts: 9

Loc: Upstate SC
Reg: 10-07-08
10-07-08 01:28 PM - Post#1537192    
    In response to chevyjim

Our 06 work truck does the same thing. It goes from COLD to HOT. Not - from cold to not as cold. But from A/C to Heat. One way to get the heat off is to simply turn the truck off. I have to do it all the time while out making deliveries. I even do it while going down the road. I know that is not smart but on hot days you do what you have to do.

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