Poor front a/c, rear a/c ok

[dhfrye]

The front a/c in my 98 Suburban does not blow very cold air. The rear units blows cool air, but not very cold air. I also hear a hissing sound outside of the rear of the vehicle when it is running.

[sgordon]

Hello, I posted a similar question last week. I was told by a repair shop that there is a "blend gate" that separates the heater core (where water from the engine flows to generate heat) from the AC "core" where coolant flows. In my case, I was told that this gate was not functioning properly and thus would not shut out air from flowing across the heater core when all I really wanted to was air from the coolant side of the system. In fact, my AC works great right up to the point that the truck warms up and the termostat opens and hot water flows through the heater core.

I've looked around and cannot determine exacting where this gate is (other than in the big box under the glove box). I've taken the top and bottom of the unit apart and have seen nothing interesting yet. I've also not found a diagram of this unit as yet and will most likely need to make a trip to the local library to get a detailed manual on how to get this thing fixed.

My posting is titled: Front AC Unit Heater/AC Gate not working

If you figure out how to get this working again, make sure that you post the answer.

Good luck.

[cris2004]

On my 98 there is a heater core valve under the hood, runs on vacuum. mabe thats what here means.
The hissing is most likely an expansion valve problem in the rear. Very common. Most AC techs pull it out and clean it or replace.
I cant imagine the heater hoses run back there or there is a vac door leaking, but I really dont know.

I had too much AC oil in my 98 once, causing a similar problem. Fixed it by opening the low point in the rear near the exhaust and letting it force out.

[jsnowbordr47]

yeah check your expansion valve, but also check your front orphis tube, I worked on my rear a/c once without checking the front orphis tube and the front wasn't hot but the rear was. Then I cleaned out hte front orhpis tube but forgot to change my filter going to the back, and I ended up with another plugged up expansion valve. my recommendation, always clean everything it the front and back when work on A/C requires total system evacuation.

[buzzkutt]

Does it get better under a load ?

[suburban_lee]

Originally Posted by buzzkutt

Does it get better under a load ?

Question - Why do you ask if it gets better under a load. My interest is that I've been having a problem with my front A/C not working 100% after being on the expressway for a while. Under a load though, say pulling a hill at 70 miles an hour or so (without a downshift, i.e. same RPMs), the A/C cools back down to where it runs in the city.

Sorry to jump in on another's forum. Maybe the info will be useful to both of us.

[Fireplug]

Thats a sure clue that your system is low on freon.
Under load the a/c pump can flow more freon through the system. That lowers the a/c outlet temp