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Very hot A/C

From : scott e nelson

Q: seems one of the sensors in my ac/heater/fan unit dont want to work right. after any amount of time it blows very hot air. if i turn the fan down to low it will start blowing cold again. could it be the hot/cold vent door forgot the name of it. the fan works fine. the temp control will make it hotter if turned to heat. also the clutch does not kick on and off on the compressor. any ideas as to what it could be tanks. .

Replies:

From : tom lawrence

also the evaporator was soaking wet on the outside i remember when i was trying to diagnose this problem. i just thought it was odd that it had moisture all over it. im not an a/c guy. ill take another look at the moisture on the evaporator. how are you able to see the evaporator its inside the hvac box behind the dash. are you referring to the accumulator which is a cylindrical container about the size of a small thermos on the passenger-side firewall your time and assistance. oh could it be a resistor on the blower motor no... the blower motor resistor simply controls the voltage supplied to the blower motor. if it goes bad then your blower motor doesnt work in anything but the highest setting. as i said the only thing the whole heater control module does to affect the a/c is to provide a ground to the pcm which then in turn energizes the clutch relay which engages the a/c clutch as long as neither the high or low pressure cutoff switch is tripped. .

From : scott e nelson

hmm i try the switch changing . also the evaporator was soaking wet on the outside i remember when i was trying to diagnose this problem. i just thought it was odd that it had moisture all over it. im not an a/c guy. ill take another look at the moisture on the evaporator. i wont be able to talk to u again till wed or thurs night. going to state babseball tourney. will let you know when i get back. i appreciate all your time and assistance. oh could it be a resistor on the blower motor even though it works for a random amount of time then blows hot like it does tanks i had forgot about the randomness part of your symptoms. yes thats strange. however the only input the pcm has that controls the a/c compressor is the input from the heater control switch and the high and low cut-off switches. the speed of the blower motor is immaterial to the operation of the a/c system. you say that if you turn the temp control to hot the air gets hotter. this tells me that the blend door is functioning properly and allowing air to pass through the heater core only when you dial the temp up. it almost sounds like it could be the evaporator freezing up which would cause the low-pressure side to drop and the low-pressure cut-out switch would disengage the compressor clutch. however if that happened as soon as the evap. thawed the clutch would automatically re-engage. the fact that when turn the blower knob down the clutch immediately re-engages blows the freeze-up theory. let me ask you this... when it cuts out if you flick the speed control down to low then back up to high in other words fiddle with the fan switch will the a/c still blow cold or does it have to go back to 1 or 2 in order to re-gain a/c function were i in your place id first try the bypass switch idea i detailed previously. barring that id put a set of gauges on the system and see what the pressures looked like when it cuts out assuming you can reproduce the problem while idling. if the gauges dont indicate anything wrong mechanically but the clutch still cuts out id replace the low-pressure switch. .

From : tom lawrence

even though it works for a random amount of time then blows hot like it does tanks i had forgot about the randomness part of your symptoms. yes thats strange. however the only input the pcm has that controls the a/c compressor is the input from the heater control switch and the high and low cut-off switches. the speed of the blower motor is immaterial to the operation of the a/c system. you say that if you turn the temp control to hot the air gets hotter. this tells me that the blend door is functioning properly and allowing air to pass through the heater core only when you dial the temp up. it almost sounds like it could be the evaporator freezing up which would cause the low-pressure side to drop and the low-pressure cut-out switch would disengage the compressor clutch. however if that happened as soon as the evap. thawed the clutch would automatically re-engage. the fact that when turn the blower knob down the clutch immediately re-engages blows the freeze-up theory. let me ask you this... when it cuts out if you flick the speed control down to low then back up to high in other words fiddle with the fan switch will the a/c still blow cold or does it have to go back to 1 or 2 in order to re-gain a/c function were i in your place id first try the bypass switch idea i detailed previously. barring that id put a set of gauges on the system and see what the pressures looked like when it cuts out assuming you can reproduce the problem while idling. if the gauges dont indicate anything wrong mechanically but the clutch still cuts out id replace the low-pressure switch. .

From : scott e nelson

the velocity stays the same as far as i remember. it immediately turns cold after 2 secs or so at the most. i dont have to wait for it to get cold. thanks. okay - then it sounds like your problem is in the ac/heater control unit. when in the two highest positions the rotary switch isnt providing a ground path for the pcms a/c switch sense and therefore the pcm is shutting off the a/c compressor. to verify this remove the dash bezel and remove the heater control. disconnect the 7-pin flat electrical connector note that theres also a 5-pin connector... we want the one with 7 pins. the two pins youre interested in are the green/white pin #2 and the black/orange pin #7. these colors are from a 2001 manual - hopefully they didnt change them from 99 but even if so the pins are still the same. now you want to test the connectors on the control module not the wiring harness just using the wiring harness to identify the pins in question. using an ohm meter you should not read any continuity between pins 2 and 7 with the controls off. with the controls in any of the a/c settings you should read continuity between those two pins. i think youll find that on the two low-speed settings you have continuity but on the two upper positions you lose continuity. if thats the case then you know for sure that your problem is in the heater controls. you have a few options... obviously you could get a replacement control from either the dealer or maybe a salvage yard. however the real low-buck solution is to just install a switch in the dash connect one terminal to a ground and connect the other terminal to an in-line tap of pin #2 on the electrical harness. that switch then becomes your manual a/c activate switch - just flip it on whenever you want the a/c to run. tom even though it works for a random amount of time then blows hot like it does tanks .

From : tom lawrence

hotter if turned to heat. also the clutch does not kick on and off on the compressor. any ideas as to what it could be tanks. its most likely the fact that you neglected to include the year/make/model of the vehicle in question. the operation of a mechanical blend door on say a 91 van will be very different than the electronic controls on say an 05 pickup. .

From : tom lawrence

ok im looking at the accumulator then....sorry okay - moisture on the accumulator is normal especially on a very humid day. the accumulator is on the low-pressure side as it the suction line and therefore they get cold. cold metal causes condensation of warm humid air. .

From : scott e nelson

also the evaporator was soaking wet on the outside i remember when i was trying to diagnose this problem. i just thought it was odd that it had moisture all over it. im not an a/c guy. ill take another look at the moisture on the evaporator. how are you able to see the evaporator its inside the hvac box behind the dash. are you referring to the accumulator which is a cylindrical container about the size of a small thermos on the passenger-side firewall ok im looking at the accumulator then....sorry your time and assistance. oh could it be a resistor on the blower motor no... the blower motor resistor simply controls the voltage supplied to the blower motor. if it goes bad then your blower motor doesnt work in anything but the highest setting. as i said the only thing the whole heater control module does to affect the a/c is to provide a ground to the pcm which then in turn energizes the clutch relay which engages the a/c clutch as long as neither the high or low pressure cutoff switch is tripped. hmm ok. .

From : scott e nelson

1999 2wd 318 pu the ac works fine on fan speed 1 and 2. fan speed 3 and 4 must close the mech blend door because it will blow hot until i turn it back to fan speed 1 or 2. except the blend door on a 99 is servo-controlled not mechanical. when it turns warm is there a decrease in velocity as well when you switch back to the lower fan speeds does it immediately turn cold or do you have to wait a while the velocity stays the same as far as i remember. it immediately turns cold after 2 secs or so at the most. i dont have to wait for it to get cold. thanks. .

From : tom lawrence

1999 2wd 318 pu the ac works fine on fan speed 1 and 2. fan speed 3 and 4 must close the mech blend door because it will blow hot until i turn it back to fan speed 1 or 2. except the blend door on a 99 is servo-controlled not mechanical. when it turns warm is there a decrease in velocity as well when you switch back to the lower fan speeds does it immediately turn cold or do you have to wait a while .

From : scott e nelson

1999 2wd 318 pu the ac works fine on fan speed 1 and 2. fan speed 3 and 4 must close the mech blend door because it will blow hot until i turn it back to fan speed 1 or 2. it will run all day on these fan speeds 1 and 2 without blowing hot air. that should narrow it down to something other than the freon clutch and compressor. hotter if turned to heat. also the clutch does not kick on and off on the compressor. any ideas as to what it could be tanks. its most likely the fact that you neglected to include the year/make/model of the vehicle in question. the operation of a mechanical blend door on say a 91 van will be very different than the electronic controls on say an 05 pickup. .

From : tom lawrence

the velocity stays the same as far as i remember. it immediately turns cold after 2 secs or so at the most. i dont have to wait for it to get cold. thanks. okay - then it sounds like your problem is in the ac/heater control unit. when in the two highest positions the rotary switch isnt providing a ground path for the pcms a/c switch sense and therefore the pcm is shutting off the a/c compressor. to verify this remove the dash bezel and remove the heater control. disconnect the 7-pin flat electrical connector note that theres also a 5-pin connector... we want the one with 7 pins. the two pins youre interested in are the green/white pin #2 and the black/orange pin #7. these colors are from a 2001 manual - hopefully they didnt change them from 99 but even if so the pins are still the same. now you want to test the connectors on the control module not the wiring harness just using the wiring harness to identify the pins in question. using an ohm meter you should not read any continuity between pins 2 and 7 with the controls off. with the controls in any of the a/c settings you should read continuity between those two pins. i think youll find that on the two low-speed settings you have continuity but on the two upper positions you lose continuity. if thats the case then you know for sure that your problem is in the heater controls. you have a few options... obviously you could get a replacement control from either the dealer or maybe a salvage yard. however the real low-buck solution is to just install a switch in the dash connect one terminal to a ground and connect the other terminal to an in-line tap of pin #2 on the electrical harness. that switch then becomes your manual a/c activate switch - just flip it on whenever you want the a/c to run. .

From : napalmheart

seems one of the sensors in my ac/heater/fan unit dont want to work right. after any amount of time it blows very hot air. if i turn the fan down to low it will start blowing cold again. could it be the hot/cold vent door forgot the name of it. the fan works fine. the temp control will make it hotter if turned to heat. also the clutch does not kick on and off on the compressor. any ideas as to what it could be tanks. no refrigerant .