a/c observations

my 90 xj seems to be having trouble keeping the a/c cold when idling or in low speed situations. Like I'll come to a stop at a light and its like the compressor clutch shuts off and the air gets warmer. When the light turns green and I take off the clutch re engages. It works great on the highway and at night. I think my high side pressure is getting too high and tripping the safety switch, so I'm not getting enough air flow through the condensor. Ive been told this is normal for these and thats why hood vents are such a popular mod. But I dont think mother chrysler would have sold very many of them with the a/c acting like this.

Ive taken a flashlight to the engine side of the radiator and I can see light through the grille. Engine temps stay where they are supposed to be. So could it be that my electric fan needs to be replaced? Or even my clutch on the mechanical fan? I replaced that two years ago trying to track down an overheating issue. Ive never heard the mechincal fan engage completely like they do on most cherokees. Well for like 10 seconds after a cold start but thats it.

tia

ECARLCL

If the cooling system isn't overheating no way the condensor is getting too hot. You probably just have a slightly low charge. You can confirm this by blocking-off some air flow with cardboard or something across the condensor. If it cools better and quits short-cycling after reducing the system "capacity" you need more Freon. Running either R-12 or now R134 for the past 5 years I've never experienced short-cycling HOT at idle in my '89. Stock compressor.

For your mechanical fan, tie a piece of kite string to a blade and secure that to something solid when HOT. Start-up, if the string breaks the clutch is probably working. However, if the gauge is within range, you don't have much to worry about.

it might be time to convert it to 134a then.... It still has the 12 in it.

I just looked at it and I guess it is short cycling. How long of a cycle is acceptable? Does the HVAC control setting affect this? I know it kicks on and off a lot when in bi-level and the fan on low. I figured that was normal. I didnt see any bubbles in the sight glass. I guess it wouldnt hurt to check the charge. I'm still baffled how it can freeze you out on the highway no matter what the temp is and in town on cooler days. But once we hit 80 degrees it isnt up to the task. If I am low on freon that means theres a leak somewhere

There are any number of things that could be going-on. Good vehicle speed will improve cooling effciency because it's a ratio thing going on with refrigeration. Drop temperature of the high pressure state (condensor) merely 4F degrees can multiply to 30F degrees or more when pressure/temperature is reduced and enters the evaporator (low pressure state) coil.

No bubbles, eh? You should check if the pressure switch next to the sight glass is opening/closing with a DVM voltage check. If it is, then you have something going on inside the pressure system. However, I'm 99% certain that switch only changes state (opens) if pressure drops too low?

There may either be a problem with the pressure switch or even the thermostat control/switch in the dash? That's a capillary tube system that senses temperature of the evaporator.

Upon thinking it over, I do experience a little cycling both city and highway driving but I think that's from the thermostatic switch simply telling the system it doesn't need any more right now. There's never a shortage of cold air from the vent box.

There are many more possibilities. Might have restriction in expansion valve or any number of things. It can get a little technical but well worth the effort if you wish to absorb manuals and troubleshooting steps. I have some 88 FSM Jeep A/C PDF's if you wish to check them out, shoot me a PM.

Startin' to get warm out there in Lenexa, eh? I lived in KC most of my life and know what you have in store for the summer!

later