Weird AC problem

If equipped with electric fan(s), make sure that they are working. They should run constant when AC is on. If not the high side pressure will go high enough to cause the high pressure switch to cut out the compressor, especially at idle. While driving, enough air flow is created thru the condensor to function almost normal, at a standstill, it won't. Get a second opinion or check the fans yourself, turn on the AC & listen if they're running. Good luck.

I don't disagree what you say could cause problems, but would it not cut off the rear AC also? Same compressor. Some of the same plumbing.

So, what different between he front and the back? Clogging orifice tube? TXV failing? Auto climate control failure of some sort (electrical)?

I would think they would flush the evaporator and change out the metering device and go on from there. And check the climate controls if electric.

Bob

Thanks for all the responses. The van does not have auto climate control. The shop fushed and cleaned the evaporato, in the first hour the front AC blew cool air then quit.

The shop wasn't sure what goes wrong? But, just want to replace evaporator.#@%$! Personally, I think second opion is an excellent idea hut hesitates that he might be screwed over again. What does E. Meyer mean by cut off valve in this situation??

Matt

Replace the evaporator? If it cools, even shortly, and there're no leaks, then it's not the evaporator. There should be one evaporator and two air circuits carrying the cold air front and aft. Something's adding hot air to the front circuit. You really need a picture of the layout of the air distribution system to go further. It could be a mixing valve--a valve that allows hot coolant into the heater core to modify the cold air, if it's too cold. Normally AC air through the evaporator never changes and to make it warmer you add heater air. Assuming there's a climate control for front and rear, look there for a problem.

Gotcha. You meant heater valve. No that one is ok. No climate contro in the front & rear.

I think E. Meyer is on the right track. On most Toyotas this valve is located in the engine compartment where the heater hose passes through the firewall into the heater core. Move your climate control levers and see if the cable on the valve moves (may require an assistant), if not then you have a broken cable and a fairly easy fix. If it moves then you have another problem. Slik

If the heater control valve is vacuum operated, take some needle nosed vice grips or some similar device & pinch off the heater hoses. I've seen cable controlled & vacuum valves that didn't close even though the external levers appeared to be moving in both directions. I've also seen rear air systems with their own compressor, completely seperate from the front system. Research what you've got in those departments for easier diagnosis. We will all be curious as to what the problem turns out to finally be. Good luck.

Heater control valve is ok. It'll fully close & open.

It sounds like you've got a vacuum problem, my friend.

Matt,

I had a Nissan Van that gave exactly the same symptom you have. Got rid of it and now have a Toyota Highlander. My problem developed gradually and while idling I could hear a hissing sound from the rear. The rear A/C was much colder than the front after warming up and running awhile.

The Nissan had two coils, one in the front and one in the rear. The front one had an oriface tube and the rear had an expansion valve. Turned out that the orifice tube was clogged slightly not allowing as much freon to flow and that put more pressure on the rear expansion valve which caused the hissing noise from time to time. I evacuated the system and with the service manual located the orifice tube. I had the tool to remove it but it broke where you pull it out so I took a small metal screw and screwed it into the center of the orifice tube and then pulled it out. Put a new one in and it completely cured the problem. On the Nissan Quest van the heating didnt affect the cooling but I'm sure a vacuum loss would interfer with the front coolness. I don't know if this is your problem but hope it helps. By the way, the A/C freon pressures were reading normal and only rose slightly when I heard the hissing sounds. Be sure your receiver dryer is not leaking the dryer compound out (white material)--mine wasn't.

Matt wrote:

Again, Thanks for all your responses. I advised my friend to take the van to dealership for second opion. It could be moisture in the system and clogged up the front orfice.