So I'm still trying to track down an issue with my A/C. The problem is that at idle, it'll blow cold. Once the RPM comes up, the temperature gets warmer. Almost seems that the higher the RPM goes, the warmer the temp gets. If you fire it up and let it sit and idle, it'll blow air that's more than cold enough. But once you start driving, you can feel it warm up. While running down the road, it stay warm till you slow down or stop again. You can actually hit the clutch and coast and feel the temperature drop.

After this problem had started, my A/C compressor went out and was replaced. Once it was replaced the A/C temps are lower than before, but the problem still exists (just more bearable now).

So what part of the A/C system would be linked to engine speed? I've though vacuum, but the blend door is electrically actuated.

 

Just a stab in the dark here--you might have a vent/blend door stuck open that is letting outside air in-

 

Do you have any pressure readings? Without that it is hard to tell if it an inside door problem or an a/c problem.

 

I only have a low side gauge, but I haven't put it on there since the new compressor went on. My concern with putting the gauges on is that everything works great at idle. The problem starts when you start driving. Can you run with gauges on the A/C system while moving?

 

Stop driving.


Sorry Justin, no real help (as usual), I can bring the A/C section from the FSM to Sedalia next weekend if you need me to.
~Rob

 

Or, you can just hang on the passenger front fender and watch the gauges while I drive. The problem is worst around 80mph, so you'll need to hold on tight.

I've got the FSM and been reading on the A/C performance, but I'm short on some of the specialty tools needed to run the diagnostics (vacuum meter, low/high side gauges). I need to track down one of the little vent thermometers so I can measure my vent output and get some hard temperature numbers.

 

I'll bring my helmet and big roll of duct tape

~Rob

 

more than likley the blend door is stuck open.

 

Will it do the same results if you keep the rpm's up to the same as 80mph sitting still? That's what I would try and have the guage hooked up as well. Low side guage is better than nothing.

 

I like that option much better

(I'll still bring my helmet, just in case. Do you think Mike might have the high/low side gauges etc?)
~Rob

 

The blend door doesn't seem stuck, since I can adjust the temperature up and down with the **** and things are blowing cold at idle. I was thinking that maybe it was blocked partially and wouldn't close to full cold, but I'd expect idle temps to be higher when the engine is warm as well.

I was kidding Rob about the 80mph thing...it actually gets noticeable at 1500rpm and higher, since it will be warmer just running down city streets.

As soon as I get a thermometer so I can actually quantify "warmer", I'll try just running the engine speed up while stopped to see if it happens.

 

how about a psi switch gone bad. or, overfilled freon. low rpm can keep psi low enough to keep compressor engaged. but at a higher rpm the psi will rise and kick on and off the compressor resulting in less compressor run time

 

Good idea, didn't really think about the switches being out of spec enough to work fine sometimes but not at others. I'll have to check them out. I'll add it to my list of things to do on Thursday when I get home.

 

The compressor is linked to engine speed. the faster the engine turns the compressor the more suction it will pull. If it is low on freon it will pull it down too low so it kicks out on low pressure. If it is over charged it will cause high pressure /low cooling.

Another thing to check is the condenser, is it dirty? dirty condenser will also cause high pressure/low cooling problems.

Check the low side pressure with the engine idled up at crusing rpms if nothing else. That will show you if it is kicking out on the low pressure switch.

Look at the pressure reading and see what the temp reading is for the evaporator. if it is below freezing it will cause it to ice up on the outside of the evap.

When they replaced your compressor did they pull a vaccumn and get all the air out? if it has air in the system it will cause poor cooling also. Also if it had moisture in the system it will cause it to ice up inside the evap coil.