Car A/C questions

[Turbo2212]

Hi guys,

Apologies if this is in the wrong section. I'm after a car A/C (I know people don't normally like this topic) expert who I can reel off a few questions at..

Firstly the pressure switch, where is it commonly located and is there a hp and lp switch or is it a duel purpose one?

Upon researching I understand there are capillary and expansion valve systems the latter with a receiver and the capillary with an accumulator instead, is that correct? What differentiates the purpose for use?

I'm aware they use clutchless compressors also, does that mean the compressor can never be turned off?

thanks

[hyperion]

HP pressure switches can sometimes be dual on newer cars. LP switches were not always fitted, however some systems cycle on the LP switch to control the cycling ON/OFF of the compressor.
Some of the early systems had a thermal fuse clipped onto the suction line near the compressor. If the temperature rose above a set point, the thermal fuse broke and stopped the supply to the electro magnetic clutch. This was often used in place of an LP switch.
There can be expansion valves fitted or CV tubes, not found any capillaries fitted. The choice is down to the system designer.
CV tubes are cheaper than expansion valves, but only provide a constant volume of refrigerant which may not respond sufficiently and cannot provide additional flow to the cooling matrix on hot days.
Most of the earlier compressors had electro magnetic clutches to enable control of the compressor.
On many of the modern systems the compressor runs constantly and the refrigerant flow through the compressor is adjusted to give a better variable volume control. It also provides for better refrigerant control at higher engine revs, preventing the compressor from overloading itself.
This type of control lends itself better to electronic temperature management to provide closer control of the cabin temperature without the fluctuations caused by switching the compressor on and off.

Hope that this helps.

[Turbo2212]

Perfect. Thank you very much

[charlie patt]

i cant remember a car that has not got a combined lp hp switch they are called trianary switches some have eprom chips in um and are on the hp circuit by the drier or pipe or if subcooled on the condensor they trip on average 300 to 320 high pressure and if standing pressure below 40 psi on average wong trip in on static this one switch protects hp and lp some vechicles have separte lp hp switches ie volvos and some agri and plant they also use these switches if a stst aint fitted ie ford ka to control temp. as far as metering goes you have a tev mainly on agri and plant but some cars use um useually with a receiver drier, ive never found a capilliary on a car but lots use a orifice system useually comes with a suction accumulator/ drier mainly vw audi group fords and french kit these are i believe used as reduce costing for manufactuer and does give a steady wave of cooling ie cuts out stalling of engine load like a tev would on small engines. the clutchless comps where brought in for several points, believe it or not on high end brands customers do not expect a clicking or cutting in of comps they want it to work but not to hear it, the second is the unit always pumps between 3 and one hundred percent they are basically controlled by a solonid valve on the back of the comp that cycles on and of the idea of them is to even load on the engine so instaed of a wot sensor the comp loads or unloads to limit load on engine when u nail the throttle etc it also assists massively in fuel economy as most of the time the comps rareley run at one hundred percent but they are highly unreliable mainly due when low of empty of gas that little pump is still pumping a little