A/C cutting out under load at highway speeds

[Fausto]

02 XLT w/60k on the clock.

A/C works perfectly fine when I'm putting around town, but will cut out (or at least the fan is cutting out) going up a grade at highway speeds. As soon as I crest the hill, everything kicks back in again.

Ideas?

 

[pa944red]

My bet is a vacuum leak.

Check the check valve on the passenger side where the vacuum lines come out of the firewall.

When you go up hill you have less vacuum, when you get to the top you coast more and create more vacuum. To test it out, take notice the next time if the air gets diverted to the defrost. That is the fail safe mode if you lose all vacuum so you can at least keep your windshield clear.

Let us know.

Tom

 

[joker1457]

I was told by a mechanic that there is a sensor that actually shuts the compresser off. It happens when you stomp on the gas or need a passing gear its so the engine doesnt have to work as hard.

Just a thought might be your issue

 

[Fausto]

I was told by a mechanic that there is a sensor that actually shuts the compresser off. It happens when you stomp on the gas or need a passing gear its so the engine doesnt have to work as hard.

Just a thought might be your issue

Yeah, I was wondering if this was a "feature", but it's honestly pretty annoying when it's hot outside and you're in rolling terrain.

 

[Fausto]

My bet is a vacuum leak.

Check the check valve on the passenger side where the vacuum lines come out of the firewall.

When you go up hill you have less vacuum, when you get to the top you coast more and create more vacuum. To test it out, take notice the next time if the air gets diverted to the defrost. That is the fail safe mode if you lose all vacuum so you can at least keep your windshield clear.

Let us know.

Tom

I'll do that, thank you.

 

[chillywilly7g]

hey guys,
Where would this check valve located?
would this check valve cause the a/c to direct airflow to the defrost when I accelerate? This happens only when I have it on the Max A/C setting only. The fan doesn't cut but the airflow changes to defrost. When I let off the pedal, it will change back towards the front vents. But when it's on any other setting (A/C front vent NON-MAX), it flows fine to the vents, even on the high fan.

Tends to be very annoying to cool the truck down quickly , especially with the 114 degree weather here in Phoenix, AZ.
115 tomorrow Saturday. and maybe 117 Sunday.... just a bit toasty.

 

[budasmoka]

40+ mph vent switch to defrost

hey guys,
Where would this check valve located?
would this check valve cause the a/c to direct airflow to the defrost when I accelerate? This happens only when I have it on the Max A/C setting only. The fan doesn't cut but the airflow changes to defrost. When I let off the pedal, it will change back towards the front vents. But when it's on any other setting (A/C front vent NON-MAX), it flows fine to the vents, even on the high fan.

Tends to be very annoying to cool the truck down quickly , especially with the 114 degree weather here in Phoenix, AZ.
115 tomorrow Saturday. and maybe 117 Sunday.... just a bit toasty.

I am having the same problem when i reach 40 to 50 mph it switches from the vents to defrost im stumped PLEASE HELP!!!!

 

[budasmoka]

Never mind I found a Vacume Resivior next to the heater core inlet/outlet next to the firewall on the passanger side of the motor and saw it was disconnected, fixed it now im crusin with a/c. I must of pulled it when I was working around it stupid me!!!

 

[Fausto]

My bet is a vacuum leak.

Check the check valve on the passenger side where the vacuum lines come out of the firewall.

When you go up hill you have less vacuum, when you get to the top you coast more and create more vacuum. To test it out, take notice the next time if the air gets diverted to the defrost. That is the fail safe mode if you lose all vacuum so you can at least keep your windshield clear.

Let us know.

Tom

Just to let you all know, this is precisely what is happening.

 

[rrgone]

Just to let you all know, this is precisely what is happening.

And that is precisely what the vacuum reservoir is suppose to prevent. Look for a leak in the reservoir, or the hoses and connectors to the reservoir.