Hi everyone,

I've got a 99 XLT, 4.2L V6. Last weekend, went on a roadtrip, high 90s temperature-wise both days, AC ran just fine. A few days later, I tried running the AC while I stepped out on my lunch break at work, and noticed that the AC would not blow cold. I checked a bit later on that day, and it still would not blow cold. On a whim, I turned the temp gauge to hot, and it would not blow hot either (on defrost, or any of the other panel selections. I had some free time this afternoon, and looked under the hood, to notice that when the AC is on, the compressor does not engage. I'm not a mechanic, and am not at all familiar with refrigeration systems in general, but I did check the continuity of the associated fuses (at least the ones that have associations in the manual), and they appear okay (the 10A under the dash in the fuse panel, and the 40A maxi-fuse in the fuse/relay cluster box under the hood). I also checked the seatings of the wiring harness/clips to make sure everything is seated securely.

That said, I am wondering if there is anything that would cause the HVAC system to neither blow hot or cold, and for the compressor to not engage?

If anyone has any ideas, I'd love to hear them, any information or comments would be appreciated.

Thanks,
Gabriel

 

does the blower motor work ? if the a/c comressor does not engage it usually means it is low on charge . the a/c system has a low pressure control on it so it will keep it from coming on if it was low.
you need to pu a pressure gauge on it to see what numbers you get .
you can get a recharge kit at the autoparts store it will come with the gauge on the can

 

Thanks for the reply! Yes, the blower motor works, but only blows unconditioned air. The compressor does not engage when the AC is selected (on either AC or MAX). I will try recharging later today and report back my results. Thanks again for the response!

Gabriel

 

Well, I picked up the Interdynamics Measure and Charge recharge / gauge combo. I'm in the red. Consistently reading at 110psi. This is not good.Tried cycling the engine, on/off, ac on/off, different combinations, hoping that something would trigger the compressor to kick on. No dice. Not sure what to do at this point. Any comments or pointers would be very appreciated.

Thanks,
Gabriel

 

at this point you need to check the pressure controls and the compressor .you will not be able to get any correct readings until you can get the system running. but it seems you dont have any major leaks.
look around the firewall you should see a acuumulator with a pressure switch on it unplug it and jumit out and see if the compressor turns on

 

Shorting the accumulator pressure switch:

I'm looking for any accumulator reference that I can find. I see nothing in the Chilton manual (reloader is right, that book says absolutely nothing about the guts of HVAC, and further implies that if you are not a mechanic, it is beyond your ability). I'm finding nothing as far as an image or diagram so I don't know what to look for.

There is a silver canister near the radiator, and there is a two-wire cable assembly attached to the top, and when you unplug it, exposes two prongs. Is this it?

Thanks,
Gabriel

 

im not familiar with the 99 f150 but that should be it you will not short it out it is a switch what will happen is you will be sending power throught the connection. and you can also disconect the power plug from the compressor and turn on the a/c and check to see if you get voltage to the compressor if you have voltage at the compressor it is a good sign tht it is no good
if ther is no voltage at the compressor the it is a problem before the compressor then it will be the saftey switches low/high pressure control selector switch , also check your fuse for the hell of it

 

I'll give this a shot when I get home from work this afternoon. Will jumper that plug on the accumulator, will then check for voltage at the compressor. I did check the associated fuses over this past weekend, I had continuity on them (the 40A in the engine compartment fuse box, and the 10A in the cabin fuse box). I'll find the associated relay(s), and swap them around to see if that may be the culprit.

Will report back later this afternoon with my findings.

Thanks again,
Gabriel

 

Okay, I jumpered the plug on the accumulator - compressor still does not engage.

I checked the voltage at the compressor - (within the plug assembly - 0.04V while idling, AC on MAX)

I swapped the associated relay with the same relay - still no engage.

I checked continuity on ALL fuses. All fuses in engine compartment fuse box check out okay.

I'm puzzled now. No power at the compressor, no engage, am wondering what to look for next.... Logic tells me that there is some sort of controller module somewhere, but I have no idea where or what to look for.

Gabriel

 

does your truck have climate control?
there is something we are missing. it has to be a control or switch problem

 

I agree, there is something else that we have not accounted for.

I have the standard AC/heat, no electronic climate control (just the ***** and selectors on the front dash panel).

What regulates the voltage to the compressor?

 

pressure switches and the selector switch on the dash
the only other thing i can think of is the selctor switch on the dash . see if there is voltage there before and after the switch is turned on

 

I am watching your posts as I am having the same type of problem on my 97 4.6. Last year I put a new compressor in and had it charged and it worked fine for a little while until the clutch went bad (damn shims). After I put a new clutch on the compressor will not engage when the AC is turned on. I know the sytem is charged but the compressor just will not turn on. A mechanic friend mentioned something to me about having to reset a fault code or something but I'm not so sure about that as I am not getting any error lights. Anyways, I am curious to see if someone comes up with a solution

Brian

 

Hey there - I'm going through sort of the same thing - I've got a 97 F150 XLT where the AC only works occasionally... and even then for only a short time. Low side is reading a constant 110Psi (so it's not a low pressure deal... eek). I haven't been able to see under the hood when it *is* working (as I'm usually driving it), but when it's not working and idling in the driveway, the compressor clutch isn't engaging. It's evidently operational for the times it's been working, and doesn't have any associated rattling thats indicative of bad shims...

Now, I disconnected and shorted the pressure switches, no dice, checked the harness going to the comp as well as associated fuses, still no dice, and am about to tear out the control housing and start testing that unit (hoping it's something dumb like that and not my compressor)...

My future father-in-law mentioned that there may be water in the system... thoughts? How would I flush the water out of the system?
Thanks in advance - I"ll keep posting if I find anything new...

 

Thanks, for chiming in! I've not been able to address my AC issues (busy work schedule lately). I've done pretty much everything you've done so far (check fuses, jumper the plugs, swap relays,etc,.). My next step is to dig into the dash to see what I can find with respect to signals being read from the cabin AC control *****.

Will check back in to post my findings.