Hey everyone. This is going to be a weird issue, but here it goes. I had the A/C on max speed with the recirculation button pressed at 65mph with the engine around 1900RPM and the fan would be running at MAX (I can hear it), but the airflow is reduced and doesn't match the fan speed. If I add power (2500-3000RPM), the airflow drops more even with the same fan speed. If I turn off the cruise control and drop it down to idle, the airflow increases and is normal for the fan speed. For some reason, even with the temperature is the same (in the 30s F), the volume of air decreases when the engine speed increases. I have no idea why. Aren't those controls vacuum operated? It runs normally and idles normally at 550rpm. I had the intake gasket replaced in 2009 at 68k and that was the only repair on this engine to my knowledge (It has 106k now). The 4x4 system works fine (the actuator pulls, but it is disconnected from the axle because I have a separate Posi-Lok system for it, so the actuator is useless, but it is still working if I choose to have it reconnected.). What else could I be missing?

 

Open the hood and spin your clutch fan if it spins real easy more than 1 revolution then replace your clutch fan. Also what is your temp running on your vehicle?

 

Fan seems fine. Spins with some resistance (I wouldn't say easy), but I have never seen it spin close to one rev. It always runs with the engine running. Temp sometimes gets to 210 on a hot day at idle, but it rarely gets above 190 all other times. Only a couple times have I seen it get beyond that. I just had the coolant changed also. Once I saw it get just above 210 climbing a hilly interstate at 65mph but that was before the coolant change. Hasn't done it before or since. Radiator was replaced 11/2007 and is clean inside and out.

Just out of curiosity, what would the engine fan have to do with the A/C electric fan? The blower fan seems to be running at constant speed, but the airflow isn't consistent with it and it lowers as the engine speed increases. It is almost like the airflow is being diverted somewhere else on it's way to the dash vents and the problem isn't there at idle or lower engine speeds. When I hit the gas, some of the airflow through the vents is lost even with the fan at MAX. Voltage is fine. 14 or just under it at speed. With everything on (headlights, 2 sets of fog lights, A/C fan, GPS, Radar detector, LEDs with only the first 3 having an effect on the voltage. I turn one off and it rises. A/C fan uses alot of power and it only reduces speed when the voltage drops when it is on MAX) it drops to around 13 at idle (halfway between the 2nd notch and 14) and returns to normal when I move. This is with a year old alternator and a brand new battery (last one was junk and failed. Lost voltage and amperage and truck would not start (nothing worked). Battery actually tested fine, but a new battery solved it anyway).

 

Believe it or not, that is normal for the air flow to drop off at higher rpm. I don't know exactly why, but I'm pretty sure every vehicle does it. It is all vacuum controlled but it takes power to run the A/C. When the engine gets a call for more power, it will cut the A/C first to deliver more power without a downshift. I don't know the specifics of how it works though. I don't know why your truck would run hot at all, it should never get above 200 unless you're towing or its extremely hot. It was over 100 here and I had the A/C cranked an it sat idling in the sun that way for 20 mins or so at the mechanic to make sure it worked and then I drove around town and the temperature gauge never budged above the 195 mark (that's with the 195° thermostat which is the recommended one or it wont run right).
I don't think the engine fan has anything to do with the climate control, unless it was a misunderstanding.

 

Sounds like a typical vacuum problem/loss. Check ALL of your vacuum hoses and PCV valve. These hoses in the engine compartment will
literally disintegrate over time. Accelerating the engine causes vacuum to fall (you probably already knew that) and that would account for the HVAC vacuum actuators to act strange.

 

Thanks for the advice.

I think it does downshift when I give it more power. It doesn't just sacrifice the A/C.

Where are the vacuum hoses in the 98? Is there a schematic somewhere? How easy are they to replace?

Could low vacuum cause other problems like slightly decreased lower power, hesitation or lower gas mileage (16 at highway speeds, 12 in town)?

 

You state the air temp coming out of the vents is in the 30s correct? There is your clue. its too cold. The low pressure control located on you accumilator is designed to turn the compressor on and off as the pressure in the system fluxuates. When pressure gets low the switch opens, when the pressure climbs it turn the compressor back on. If the low pressure control fails in the closed position, the compressure will continue to run no matter how low the pressure gets.
When the pressure is low, the refrigerant in the evaporator is boiling at a colder temperature. In air conditioning, this temperature cannot go below freezing or ice will form on the evaporator coil. This ice will block air flow.

The reason this occurs when it does it due to the engine speed. The compressor is turning faster which mean it has more capacity. (Forms ice) When you let the RPM drop, the compressor capacity drops and the warm air blowing through it melts the ice therefor removing the restriction.
If you dont hear the compressor cycling on and off, I would make sure nobody jumpered out the low pressure contol first, If it isnt jumpered, them I would test it. It should be a closed circuit with the engine off. If you unplug the switch and remove it, it should be an open circuit. (This switch can be removed without blowing the charge.)
Good luck!

 

You bet it is cold. I got too used to the winters in upstate NY that I have the A/C on full blast in the summer. I turn it to MAX COLD. I used the IR thermometer and sometimes it is in the high 20s. It could be in the 90s outside and I could start to shiver. When I get out of the car, my glasses fog up.

The compressor definitely cycles on and off. I could definitely feel it. Feels like I have a second transmission and the compressor definitely robs some power. Enough that on hills if I need more power, I turn off the A/C.

I always have to recharge the freon every spring because there is a leak somewhere (don't know where it is, don't want to know, cheaper to charge it every spring), but the pressure is correct for the temperature and holds at it with the compressor on at idle. It drops when I rev the engine and starts to cycle as normal. Sometimes (but not often) I add a can of PAG oil to keep the compressor lubricated.

This seems to be a vacuum issue. The electrical parts, compressor and related stuff seem fine. This seems to be a vac actuator issue since the vacuum pressure drops a bit with engine speed. The question is where could it be.

 

I hear what you are saying. But the evaporator temperature should never drop below freezing.

You say you need to add refrigerant every year. Perhaps it is over charged? What is your high side pressure like? What are the pressures that your compressor is cycling on and off?

Is the suction line sweaty? frosted? That would be a sign that you are over-charged.

 

Every year because by Spring it is empty. Just above ZERO PSI on the low side. It leaks out mostly during the winter. Maybe I have a seal that shrinks with the low NY winter temperatures that is allowing the freon to leak out slowly. I tried freon with the weak type of stop leak a couple times a year or two ago (NOT the one that claims to seal holes in metal and can seal the fill port), but that is useless and I stopped using it.

I add enough freon for it to maintain the pressure indicated on the gauge for the ambient temperature. Maybe even a bit lower. The compressor is on continuously at idle to maintain that pressure. I revved the engine after putting the freon in and the pressure dropped slowly until the compressor switched off. Once the pressure climbed again, it switched on as normal. Once I get the car moving, it cycles on and off as normal and I can feel and hear it doing that. I don't have the gauge with me right now (somewhere buried in the trunk), but it cycles on when it gets near the red zone and switches off when it gets to the bottom of the green zone. As I mentioned, at idle, it stays steady when the A/C is on with the engine idling. Doesn't change unless the engine is moving faster than idle.

I can't tell what the high side is. I don't have the gauge for that port. Just the normal low side port hose that connects to the can with a pressure gauge.

Where is the suction line?

Those temps are with the IR thermometer pointed into the airflow, so I don't know if those are even accurate. It is as cold as it always was, maybe just a bit colder.