I recently changed my old r12 to 134a. did the who;e conversion etc. my ac cuts out when the car is at idle or cruising speed. also the blower kicks of when the compressor kicks off. i donty under stand if its a relay or somthing else?? i just changed the blower motor but that didnt help anything MIKE

How much freon did you put back in the system? Did you pull a vaccum?

i put 2 and a half cans of 134 a back in. thast all it would take. no i did pull a vaccum. the fan motor and compressor kick on and off at the same time. i just changed the fan motor. that did not help me. sometimes it stays on the whole drive then sometimes it kicks on for 2 minutes then shuts off.. on/off/on/off etc.

From my experience, when the AC compressor kicks on and off every few seconds its low on freon.

This may not be any help, just though I'd share.


Max,

typical problem on these would be the low pressure switch loosing contact, but you say the blower stops at the same time. So that would change things, Somthing in the hvac switch panel maybe? im trying to think what circuit woudl cut out that would make compressor AND blower turn off.

Yes both shut on and off at the same time. its really strange. the freon is good i even tried another half a can and it took. but still the same problem. i replaced the resistor as well when i changed the fan blower. drove it the other day and it kicked on and off about 20 times while driving then it stayed on for about 40 miles till i got to my destination and shut it off. same problem on the way home. i also changed the hi-lo fan speed selector and the switch behind the control panel that selects the off/max/norm/vent def still the same problem.

Is the fan the cooling/ac fan or the blower motor?If its the cooling fan then its normal for it cycle with the ac comp. It does so to keep the high side pressure from going too high.

The freon charge amount is critical. To much is just as bad as not enough, as is air in the system...which will surely be in it if you didn't pull a vacuum for at least 30 min. The capacity should be 15% of the R12, and then you can add a little at a time if needed to get the pressures right, which brings me to the next thing...do you have a set of ac gauges or just using cans of freon from the parts store? Having said that, I would suggest that if you don't have an ac machine that'll pull a vacuum and measure the charge then your best bet would be take it to a shop that has the equipment and experiance to do it properly.

yes i think im going to have a vac pullled and a recharge. but we are talking about the BLOWER motor cycling on and off with the compressor NOT the engine fan. Blower motor should be constant. thats why i think its a relay somewhere. still stumped

The blower motor cycling with the ac comp is very wierd...been working on cars 15yrs and never seen that before.Does the fan work normally with the control set to other positions other than ac?If you can get your hands on some wiring diagrams look for some type of common link.

You're positive that it's not just the blower motor turning on and off? I mean, you were under the hood and saw/heard the blower motor turn off as well as the compressor, right? You might want to look at the control unit in the car too. If you pop out the hvac control panel, the panel has 3 individual switches that can go bad. One is the switch, the part attached to the blower knob. The 2nd is the switch attached to the slide bars, and the 3rd is the vaccuum switch. I recently had the 2nd switch go bad. Over the years of sliding back and forth, a sliver of copper broke off from the contact bars and bridged the gap between a couple of the "settings" causing the switch to burn up when you set the ac to any of those settings.

Make sure all those switches are in good shape. I'm not sure if this could cause your issue, but when I set the controls to the bridged settings the system did kick on and off occasionally as the switch slowly burnt up.

im absolutly positive that the blower and the compressor kick on and off simultainously. ive actually cahnged the blower motor switch (hi-lo) and the slider switch as well. as far as the vaccum switch where is that? i think its the round one that has all the vac lines attatched correct? maybe that should be my next step. is there a relay under the hood or fuse panel that i need to know about? thanks for your help.

I don't personally know of any relay or fuses, but there could be some. There's another item, but I highly doubt it has anything to do with this as its part of the blower fan setup. There is a, resistor? or something near the blower motor. Should be to the right of it attached to the box to the right of the motor(when you're looking at it from under the hood). If you remove the 2 screws and the plug attached, underneath there's all sorts of curly wires and such. As I said, I HIGHLY doubt that is a problem as they just don't seem to ever go bad, plus it shouldn't have any effect on the compressor.

The only thing I can think of that would cause both to go on and off at the same time would be the hvac control unit, or one of the switches inside it. You know... You may want to try a little test. Go to your local junkyard, find a car with a decent looking hvac control unit, remove it, and temporarily swap it with yours. I can't see it costing more than 5-10 dollars, and it sure can't hurt to try a completely different unit. But yes, the vacuum switch is that whiteish colored round piece with all the vacuum hoses going into it. I've found all 3 of those switches on rock auto, the ones attached to the control unit. Blower switch, slider switch and vacuum switch.

I can't really imagine what's causing this though. Making both go on and off at the same time is just odd unless it's directly in the control unit. If the fuses for all those things are good but you haven't replaced them because they look good, might be a sounds idea to just buy a box of fuses and clean house in the fuse box. Poke around behind the control unit with a flashlight too, check for crimps, frayed wires, anything funny looking too. Whatever is causing it has to be between the control unit and the compressor and blower.

I suppose it could be a power issue. But only at idle? It sounds like a break in the slider siwtch, but you replaced that. I guess the vacuum switch, fuses and swapping the control unit temporarily is the only option.

Does the blower fan ever go off at idle if the AC is off? or heat is on? Try both of those, although having the heat on might be annoying to test. If it ONLY goes off when the AC is on and never with any other setting, then it has to be involved with the compressor somehow. Make sure you try EVERY setting on the unit, max/normal/fan/heat/defrost, whatever. Just to rule things out.

I can't see how this would effect anything, but also check this. On my compressor, there is a roundish plug on the compressor. Right where the wires enter the plug connector, the wires were exposed with melted wire coating around them. Never caused a problem, but I did buy a replacement plug as it just looked unsafe. Check all the plugs and wires attached to the compressor, blower motor, relays, resistors, drier, anything.

Another question...does the blower motor cycle with the A/C on all speeds, or just on the high speed setting? I ask because there is a high speed blower relay that also goes to the A/C compressor. That maybe your problem, its looks like its located underhood near the accumulator.

yes it cycles on and off at all speeds. i will look for the relay and replace. process of elimination i guess.