Do you have one of the set of pliers you can use on the heater hoses to pinch it and clamp it off temporairly, I know they make them for diagnostic purposes. You could use this to isolate the heater core-------------

The only other thing I could think of would be a "weak" compressor.

When you do find out what it is, let us know for future ref.

 

OK, bringing this one back to the top. Been out of town for a few weeks, so I haven't had a chance to do any more testing or take it in for repair.

I put my low side gauge on today with a can of R134 to see if the system might be low now. At idle, with an outside air temp of 87*, the low side reads ~45psi. If I ramp the engine speed up to 1000rpm, the low side pressure drops to ~35psi. If I continue to increase engine speed, the pressure continues to drop.

According to the chart in the FSM, with an ambient temp of 90*, the low side pressure should be 50-60psi at 1000rpm. My question is, should the low side pressure be dropping as the RPM increases, or should it increase?

I don't have a high side gauge, so I can't tell what those pressures are. And the compressor clutch was engaged while I was testing. I actually never heard it disengage the entire time I was connected. At a steady RPM, the pressure also stayed steady and did not fluctuate.

I'm inclined to rule out the heater core as causing the problem, since it will occur even when I first start up before the water temp has had a chance to increase.

 

Whats the temperature of the air coming out of you vents when its working properly? Use a meat thermometer.

 

This is my first time replying on this site. I am wondering if you have found the problem because my 99 is doing the same thing. Good around town and then when you get on the highway and the rpm's level off it goes to outside air temperature. Now with mine if I accelerate or come to a hill when you call for more rpm's, it is cold again.........Any info would help..Thanks LTW

 

It is normal for low side pressures to DROP (not rise) with an increase of RPM. Remember that the low side is the suction side. The orifice tube causes a restriction in the system. The compressor "sucks against" this restriction, creating a reduced pressure on the downstream side and a high pressure on the upstream side. The harder the compressor pumps, the stronger it sucks against the restriction. So it can be expected to follow the pattern aggiejustin reports -- lower "low side" pressure with higher RPM.

The low-side pressures aggiejustin quotes are higher than what I see in my 1995 Dodge FSM, and are higher than I would expect from my experience with other vehicles (and from the physics of R134a for that matter). It is possible he's reading the chart wrong. Maybe his "autozone" low-side guage is off. I don't mean in any way to be critical, just trying to reconcile the information...

The behavior he's reporting is somewhat consistent with an overcharged system. Remember that refrigerant is not "cold juice", and too much makes the system warmer, not colder. Another less likely possibility is excessive air in the system -- perhaps from recharging a totally discharged system from a can without pulling a vacuum.

It would be nice to see the high side pressures (and duct temperatures) to confirm this. Also -- for the charts and pressures to be meaningful you have to set up the vehicle as recommended by the FSM. Typically, A/C on recirc, fan on full blast, interior temp stabilized at 70 to 80 degrees. Engine at specified RPM. In the 1995 manual Dodge recommends jumpering the cycling switch as needed for the purposes of measuring pressures. From the sound of aggies system, the low side pressure is so high that it never cycles anyway.

 

No AC man by any stretch, but it sounds a little low to me at idle, (charge), not much though, just a few ounces, yeah it should pull down at higher rpms becasue of the compressor doing it's job, should pull down and then cycle off at higher rpms,

If you decide to add some just make sure and add a very little at a time, let it idle and stabalize, watching the gauge.

 

sound like you already have enough 134 in your system better double check

 

Well, the problem has finally shown itself. It's the compressor that's dying. Last night when I started it up, the compressor made a horrible noise when it first engaged, then it was quiet. Today, whenever it engages you can hear it groaning while the clutch is engaged. After talking with my cousin who runs a repair shop, he was saying the compressor has probably been slowly dying and there are some metal particles from the compressor that got into the orifice tube that were blocking the flow. So when the RPMs went up, it was causing the tube to be blocked more than at idle. Now that the compressor is "crying", it looks like it's time for a new one.

 

can someone tell me where to find this blend door. my a/c only blows uoy the top or bottom..... not out the front..... ice cold though. thanks

 

where do i find this blend door.... mine is blowing out the top only

 

your not going to like what i have to say but the door is in behind the dash on the passenger side of the truck

 

Can you switch between the floor vents and the defrost vents? Or is it stuck on only one? If it's stuck, check your vacuum lines door to control where air is being delivered is vacuum controlled.

 

i can switch between the floor/defrost/and front but only the floor and defrost blow air out.... nothing blows out the front

 

Fan clutch acting up?