1999 gmc Jimmy only Blows hot air. Diverter actuator is moving and working. Even when compressor starts all pipes are hot. Check 134A and was low. When put in less than a can the compressor would cycle on and off but still very hot air. Help please

No ,there is not another valve . One low side service port an one high side service port . An only one A/C compressor . Under the hood in the engine compartment there are A/C lines going into the firewall . These go to the front Evaparator unit . With the vehicle running an A/C on do this line's (pipes) get cold ? If yes , your problem is probably the temp. actuator . Control's how hot or cold the air coming from the vent's get . If stuck half way , hot an cold air combine to make warm air . Replacing some of these actuators can require the dash to be removed . Your best bet ,take it to a qualified repair shop .

Could be that the heater core is disconnected, there are two hoses that attach to the heather core that come out of the engine, this provides hot water to the core thus making the heater work, when the heater core starts leaking water the quick and fast fix would be to bypass the heater core and connect the two hoses together, check under the hood on the left passenger side there should be two hoses about 1" thick see if there are connected together or of they seem to be connected to 2 outlets that come out of the inside of the vehicle. people do that specially if selling vehicle.

Make sure the pressure is 25 to 45 psi on the low side and that the pipes are getting cold on the low side.

Could be the vacuum controlled motors inside the dash.

Set climate control to hot then cold or the temperature control lever from hot to cold and listen for the vacuum motor operating the flap inside that changes the flow from the heater core to the evaporator inside the dash area.

Good luck to you.

check the fuse and the wires.

If you still get cold air out of the rear vents but the front only blows hot air you may have a bad temp door actuator in the dash, it may be stuck on hot and not able to move to cold air. However if you are low on freon with a truck that has front and rear ac then there will be a temp diff between the two. If it is hot air out the front like the heat is on then you have that actuator problem but if it is cool air about the same as the outside air temp then you may be low on freon.

check the HVAC relay under the hood for +12 volts if you have it here, then check the compressor clutch coil for +12 volts,then check the low pressure switch on the receiver on the passenger side of the engine compartment by jumping the switch and see if the compressor starts,then if you can hear the clutch engage and the compressor starts then you are low on R-134a refrigerant and need to find the leak or top it off with an a/c recharge kit,but be careful not to add too much refrigerant

Before you add freon to measure how much freon is clucht checks if the compressor is activated when you connect the air conditioner if the clucht not activated and have a good pressure in the system looks at low pressure switch that goes in the drier and that very often these are damaged, you also have to check the fuse and relay the compresor.Thanks

check to see if ac compressor is turning ,if so look to see if cooling fan/fans are working if not check fuses,and cooling fan relays/if ac is turning and cooling fan/fans are working ,need to put gauges on ac system and check pressures ,if normal ,and ac low side pipe/lines/hoses are cols then it is ur actuator motor for the temp door that is not working

sound like ac vent or air door is not open.your ac mode switch is bad or the ac air door actutator is not getting vacuum .check vacuum lines to ac switch.besure disable air bags when working around steering area or dash.

the low pressure port is the charging port, this port is either in the low pressure line or the accumulator that the low pressure lines to to (can shaped object), the low pressure line is the larger of the two lines from the compressor.